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authorRusty Russell <rusty@rustcorp.com.au>2007-10-21 21:01:54 -0400
committerRusty Russell <rusty@rustcorp.com.au>2007-10-23 01:49:50 -0400
commit34b8867a034364ca33d0adb3a1c5b9982903c719 (patch)
tree7b6385b3985e7bdcca91103d01dea9f707e8b567 /drivers/lguest
parentc37ae93d597fc63bae979db76b527dcc7740dc9d (diff)
Move lguest guest support to arch/x86.
Lguest has two sides: host support (to launch guests) and guest support (replacement boot path and paravirt_ops). This moves the guest side to arch/x86/lguest where it's closer to related code. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Cc: Andi Kleen <ak@suse.de>
Diffstat (limited to 'drivers/lguest')
-rw-r--r--drivers/lguest/Makefile4
-rw-r--r--drivers/lguest/lguest.c1106
-rw-r--r--drivers/lguest/lguest_asm.S93
3 files changed, 2 insertions, 1201 deletions
diff --git a/drivers/lguest/Makefile b/drivers/lguest/Makefile
index e5047471c334..2db98c233e54 100644
--- a/drivers/lguest/Makefile
+++ b/drivers/lguest/Makefile
@@ -1,5 +1,5 @@
1# Guest requires the paravirt_ops replacement and the bus driver. 1# Guest requires the bus driver.
2obj-$(CONFIG_LGUEST_GUEST) += lguest.o lguest_asm.o lguest_bus.o 2obj-$(CONFIG_LGUEST_GUEST) += lguest_bus.o
3 3
4# Host requires the other files, which can be a module. 4# Host requires the other files, which can be a module.
5obj-$(CONFIG_LGUEST) += lg.o 5obj-$(CONFIG_LGUEST) += lg.o
diff --git a/drivers/lguest/lguest.c b/drivers/lguest/lguest.c
deleted file mode 100644
index 8e9e485a5cfa..000000000000
--- a/drivers/lguest/lguest.c
+++ /dev/null
@@ -1,1106 +0,0 @@
1/*P:010
2 * A hypervisor allows multiple Operating Systems to run on a single machine.
3 * To quote David Wheeler: "Any problem in computer science can be solved with
4 * another layer of indirection."
5 *
6 * We keep things simple in two ways. First, we start with a normal Linux
7 * kernel and insert a module (lg.ko) which allows us to run other Linux
8 * kernels the same way we'd run processes. We call the first kernel the Host,
9 * and the others the Guests. The program which sets up and configures Guests
10 * (such as the example in Documentation/lguest/lguest.c) is called the
11 * Launcher.
12 *
13 * Secondly, we only run specially modified Guests, not normal kernels. When
14 * you set CONFIG_LGUEST to 'y' or 'm', this automatically sets
15 * CONFIG_LGUEST_GUEST=y, which compiles this file into the kernel so it knows
16 * how to be a Guest. This means that you can use the same kernel you boot
17 * normally (ie. as a Host) as a Guest.
18 *
19 * These Guests know that they cannot do privileged operations, such as disable
20 * interrupts, and that they have to ask the Host to do such things explicitly.
21 * This file consists of all the replacements for such low-level native
22 * hardware operations: these special Guest versions call the Host.
23 *
24 * So how does the kernel know it's a Guest? The Guest starts at a special
25 * entry point marked with a magic string, which sets up a few things then
26 * calls here. We replace the native functions various "paravirt" structures
27 * with our Guest versions, then boot like normal. :*/
28
29/*
30 * Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation.
31 *
32 * This program is free software; you can redistribute it and/or modify
33 * it under the terms of the GNU General Public License as published by
34 * the Free Software Foundation; either version 2 of the License, or
35 * (at your option) any later version.
36 *
37 * This program is distributed in the hope that it will be useful, but
38 * WITHOUT ANY WARRANTY; without even the implied warranty of
39 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
40 * NON INFRINGEMENT. See the GNU General Public License for more
41 * details.
42 *
43 * You should have received a copy of the GNU General Public License
44 * along with this program; if not, write to the Free Software
45 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
46 */
47#include <linux/kernel.h>
48#include <linux/start_kernel.h>
49#include <linux/string.h>
50#include <linux/console.h>
51#include <linux/screen_info.h>
52#include <linux/irq.h>
53#include <linux/interrupt.h>
54#include <linux/clocksource.h>
55#include <linux/clockchips.h>
56#include <linux/lguest.h>
57#include <linux/lguest_launcher.h>
58#include <linux/lguest_bus.h>
59#include <asm/paravirt.h>
60#include <asm/param.h>
61#include <asm/page.h>
62#include <asm/pgtable.h>
63#include <asm/desc.h>
64#include <asm/setup.h>
65#include <asm/e820.h>
66#include <asm/mce.h>
67#include <asm/io.h>
68
69/*G:010 Welcome to the Guest!
70 *
71 * The Guest in our tale is a simple creature: identical to the Host but
72 * behaving in simplified but equivalent ways. In particular, the Guest is the
73 * same kernel as the Host (or at least, built from the same source code). :*/
74
75/* Declarations for definitions in lguest_guest.S */
76extern char lguest_noirq_start[], lguest_noirq_end[];
77extern const char lgstart_cli[], lgend_cli[];
78extern const char lgstart_sti[], lgend_sti[];
79extern const char lgstart_popf[], lgend_popf[];
80extern const char lgstart_pushf[], lgend_pushf[];
81extern const char lgstart_iret[], lgend_iret[];
82extern void lguest_iret(void);
83
84struct lguest_data lguest_data = {
85 .hcall_status = { [0 ... LHCALL_RING_SIZE-1] = 0xFF },
86 .noirq_start = (u32)lguest_noirq_start,
87 .noirq_end = (u32)lguest_noirq_end,
88 .blocked_interrupts = { 1 }, /* Block timer interrupts */
89};
90static cycle_t clock_base;
91
92/*G:035 Notice the lazy_hcall() above, rather than hcall(). This is our first
93 * real optimization trick!
94 *
95 * When lazy_mode is set, it means we're allowed to defer all hypercalls and do
96 * them as a batch when lazy_mode is eventually turned off. Because hypercalls
97 * are reasonably expensive, batching them up makes sense. For example, a
98 * large mmap might update dozens of page table entries: that code calls
99 * paravirt_enter_lazy_mmu(), does the dozen updates, then calls
100 * lguest_leave_lazy_mode().
101 *
102 * So, when we're in lazy mode, we call async_hypercall() to store the call for
103 * future processing. When lazy mode is turned off we issue a hypercall to
104 * flush the stored calls.
105 */
106static void lguest_leave_lazy_mode(void)
107{
108 paravirt_leave_lazy(paravirt_get_lazy_mode());
109 hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0);
110}
111
112static void lazy_hcall(unsigned long call,
113 unsigned long arg1,
114 unsigned long arg2,
115 unsigned long arg3)
116{
117 if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
118 hcall(call, arg1, arg2, arg3);
119 else
120 async_hcall(call, arg1, arg2, arg3);
121}
122
123/* async_hcall() is pretty simple: I'm quite proud of it really. We have a
124 * ring buffer of stored hypercalls which the Host will run though next time we
125 * do a normal hypercall. Each entry in the ring has 4 slots for the hypercall
126 * arguments, and a "hcall_status" word which is 0 if the call is ready to go,
127 * and 255 once the Host has finished with it.
128 *
129 * If we come around to a slot which hasn't been finished, then the table is
130 * full and we just make the hypercall directly. This has the nice side
131 * effect of causing the Host to run all the stored calls in the ring buffer
132 * which empties it for next time! */
133void async_hcall(unsigned long call,
134 unsigned long arg1, unsigned long arg2, unsigned long arg3)
135{
136 /* Note: This code assumes we're uniprocessor. */
137 static unsigned int next_call;
138 unsigned long flags;
139
140 /* Disable interrupts if not already disabled: we don't want an
141 * interrupt handler making a hypercall while we're already doing
142 * one! */
143 local_irq_save(flags);
144 if (lguest_data.hcall_status[next_call] != 0xFF) {
145 /* Table full, so do normal hcall which will flush table. */
146 hcall(call, arg1, arg2, arg3);
147 } else {
148 lguest_data.hcalls[next_call].eax = call;
149 lguest_data.hcalls[next_call].edx = arg1;
150 lguest_data.hcalls[next_call].ebx = arg2;
151 lguest_data.hcalls[next_call].ecx = arg3;
152 /* Arguments must all be written before we mark it to go */
153 wmb();
154 lguest_data.hcall_status[next_call] = 0;
155 if (++next_call == LHCALL_RING_SIZE)
156 next_call = 0;
157 }
158 local_irq_restore(flags);
159}
160/*:*/
161
162/* Wrappers for the SEND_DMA and BIND_DMA hypercalls. This is mainly because
163 * Jeff Garzik complained that __pa() should never appear in drivers, and this
164 * helps remove most of them. But also, it wraps some ugliness. */
165void lguest_send_dma(unsigned long key, struct lguest_dma *dma)
166{
167 /* The hcall might not write this if something goes wrong */
168 dma->used_len = 0;
169 hcall(LHCALL_SEND_DMA, key, __pa(dma), 0);
170}
171
172int lguest_bind_dma(unsigned long key, struct lguest_dma *dmas,
173 unsigned int num, u8 irq)
174{
175 /* This is the only hypercall which actually wants 5 arguments, and we
176 * only support 4. Fortunately the interrupt number is always less
177 * than 256, so we can pack it with the number of dmas in the final
178 * argument. */
179 if (!hcall(LHCALL_BIND_DMA, key, __pa(dmas), (num << 8) | irq))
180 return -ENOMEM;
181 return 0;
182}
183
184/* Unbinding is the same hypercall as binding, but with 0 num & irq. */
185void lguest_unbind_dma(unsigned long key, struct lguest_dma *dmas)
186{
187 hcall(LHCALL_BIND_DMA, key, __pa(dmas), 0);
188}
189
190/* For guests, device memory can be used as normal memory, so we cast away the
191 * __iomem to quieten sparse. */
192void *lguest_map(unsigned long phys_addr, unsigned long pages)
193{
194 return (__force void *)ioremap(phys_addr, PAGE_SIZE*pages);
195}
196
197void lguest_unmap(void *addr)
198{
199 iounmap((__force void __iomem *)addr);
200}
201
202/*G:033
203 * Here are our first native-instruction replacements: four functions for
204 * interrupt control.
205 *
206 * The simplest way of implementing these would be to have "turn interrupts
207 * off" and "turn interrupts on" hypercalls. Unfortunately, this is too slow:
208 * these are by far the most commonly called functions of those we override.
209 *
210 * So instead we keep an "irq_enabled" field inside our "struct lguest_data",
211 * which the Guest can update with a single instruction. The Host knows to
212 * check there when it wants to deliver an interrupt.
213 */
214
215/* save_flags() is expected to return the processor state (ie. "eflags"). The
216 * eflags word contains all kind of stuff, but in practice Linux only cares
217 * about the interrupt flag. Our "save_flags()" just returns that. */
218static unsigned long save_fl(void)
219{
220 return lguest_data.irq_enabled;
221}
222
223/* "restore_flags" just sets the flags back to the value given. */
224static void restore_fl(unsigned long flags)
225{
226 lguest_data.irq_enabled = flags;
227}
228
229/* Interrupts go off... */
230static void irq_disable(void)
231{
232 lguest_data.irq_enabled = 0;
233}
234
235/* Interrupts go on... */
236static void irq_enable(void)
237{
238 lguest_data.irq_enabled = X86_EFLAGS_IF;
239}
240/*:*/
241/*M:003 Note that we don't check for outstanding interrupts when we re-enable
242 * them (or when we unmask an interrupt). This seems to work for the moment,
243 * since interrupts are rare and we'll just get the interrupt on the next timer
244 * tick, but when we turn on CONFIG_NO_HZ, we should revisit this. One way
245 * would be to put the "irq_enabled" field in a page by itself, and have the
246 * Host write-protect it when an interrupt comes in when irqs are disabled.
247 * There will then be a page fault as soon as interrupts are re-enabled. :*/
248
249/*G:034
250 * The Interrupt Descriptor Table (IDT).
251 *
252 * The IDT tells the processor what to do when an interrupt comes in. Each
253 * entry in the table is a 64-bit descriptor: this holds the privilege level,
254 * address of the handler, and... well, who cares? The Guest just asks the
255 * Host to make the change anyway, because the Host controls the real IDT.
256 */
257static void lguest_write_idt_entry(struct desc_struct *dt,
258 int entrynum, u32 low, u32 high)
259{
260 /* Keep the local copy up to date. */
261 write_dt_entry(dt, entrynum, low, high);
262 /* Tell Host about this new entry. */
263 hcall(LHCALL_LOAD_IDT_ENTRY, entrynum, low, high);
264}
265
266/* Changing to a different IDT is very rare: we keep the IDT up-to-date every
267 * time it is written, so we can simply loop through all entries and tell the
268 * Host about them. */
269static void lguest_load_idt(const struct Xgt_desc_struct *desc)
270{
271 unsigned int i;
272 struct desc_struct *idt = (void *)desc->address;
273
274 for (i = 0; i < (desc->size+1)/8; i++)
275 hcall(LHCALL_LOAD_IDT_ENTRY, i, idt[i].a, idt[i].b);
276}
277
278/*
279 * The Global Descriptor Table.
280 *
281 * The Intel architecture defines another table, called the Global Descriptor
282 * Table (GDT). You tell the CPU where it is (and its size) using the "lgdt"
283 * instruction, and then several other instructions refer to entries in the
284 * table. There are three entries which the Switcher needs, so the Host simply
285 * controls the entire thing and the Guest asks it to make changes using the
286 * LOAD_GDT hypercall.
287 *
288 * This is the opposite of the IDT code where we have a LOAD_IDT_ENTRY
289 * hypercall and use that repeatedly to load a new IDT. I don't think it
290 * really matters, but wouldn't it be nice if they were the same?
291 */
292static void lguest_load_gdt(const struct Xgt_desc_struct *desc)
293{
294 BUG_ON((desc->size+1)/8 != GDT_ENTRIES);
295 hcall(LHCALL_LOAD_GDT, __pa(desc->address), GDT_ENTRIES, 0);
296}
297
298/* For a single GDT entry which changes, we do the lazy thing: alter our GDT,
299 * then tell the Host to reload the entire thing. This operation is so rare
300 * that this naive implementation is reasonable. */
301static void lguest_write_gdt_entry(struct desc_struct *dt,
302 int entrynum, u32 low, u32 high)
303{
304 write_dt_entry(dt, entrynum, low, high);
305 hcall(LHCALL_LOAD_GDT, __pa(dt), GDT_ENTRIES, 0);
306}
307
308/* OK, I lied. There are three "thread local storage" GDT entries which change
309 * on every context switch (these three entries are how glibc implements
310 * __thread variables). So we have a hypercall specifically for this case. */
311static void lguest_load_tls(struct thread_struct *t, unsigned int cpu)
312{
313 /* There's one problem which normal hardware doesn't have: the Host
314 * can't handle us removing entries we're currently using. So we clear
315 * the GS register here: if it's needed it'll be reloaded anyway. */
316 loadsegment(gs, 0);
317 lazy_hcall(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu, 0);
318}
319
320/*G:038 That's enough excitement for now, back to ploughing through each of
321 * the different pv_ops structures (we're about 1/3 of the way through).
322 *
323 * This is the Local Descriptor Table, another weird Intel thingy. Linux only
324 * uses this for some strange applications like Wine. We don't do anything
325 * here, so they'll get an informative and friendly Segmentation Fault. */
326static void lguest_set_ldt(const void *addr, unsigned entries)
327{
328}
329
330/* This loads a GDT entry into the "Task Register": that entry points to a
331 * structure called the Task State Segment. Some comments scattered though the
332 * kernel code indicate that this used for task switching in ages past, along
333 * with blood sacrifice and astrology.
334 *
335 * Now there's nothing interesting in here that we don't get told elsewhere.
336 * But the native version uses the "ltr" instruction, which makes the Host
337 * complain to the Guest about a Segmentation Fault and it'll oops. So we
338 * override the native version with a do-nothing version. */
339static void lguest_load_tr_desc(void)
340{
341}
342
343/* The "cpuid" instruction is a way of querying both the CPU identity
344 * (manufacturer, model, etc) and its features. It was introduced before the
345 * Pentium in 1993 and keeps getting extended by both Intel and AMD. As you
346 * might imagine, after a decade and a half this treatment, it is now a giant
347 * ball of hair. Its entry in the current Intel manual runs to 28 pages.
348 *
349 * This instruction even it has its own Wikipedia entry. The Wikipedia entry
350 * has been translated into 4 languages. I am not making this up!
351 *
352 * We could get funky here and identify ourselves as "GenuineLguest", but
353 * instead we just use the real "cpuid" instruction. Then I pretty much turned
354 * off feature bits until the Guest booted. (Don't say that: you'll damage
355 * lguest sales!) Shut up, inner voice! (Hey, just pointing out that this is
356 * hardly future proof.) Noone's listening! They don't like you anyway,
357 * parenthetic weirdo!
358 *
359 * Replacing the cpuid so we can turn features off is great for the kernel, but
360 * anyone (including userspace) can just use the raw "cpuid" instruction and
361 * the Host won't even notice since it isn't privileged. So we try not to get
362 * too worked up about it. */
363static void lguest_cpuid(unsigned int *eax, unsigned int *ebx,
364 unsigned int *ecx, unsigned int *edx)
365{
366 int function = *eax;
367
368 native_cpuid(eax, ebx, ecx, edx);
369 switch (function) {
370 case 1: /* Basic feature request. */
371 /* We only allow kernel to see SSE3, CMPXCHG16B and SSSE3 */
372 *ecx &= 0x00002201;
373 /* SSE, SSE2, FXSR, MMX, CMOV, CMPXCHG8B, FPU. */
374 *edx &= 0x07808101;
375 /* The Host can do a nice optimization if it knows that the
376 * kernel mappings (addresses above 0xC0000000 or whatever
377 * PAGE_OFFSET is set to) haven't changed. But Linux calls
378 * flush_tlb_user() for both user and kernel mappings unless
379 * the Page Global Enable (PGE) feature bit is set. */
380 *edx |= 0x00002000;
381 break;
382 case 0x80000000:
383 /* Futureproof this a little: if they ask how much extended
384 * processor information there is, limit it to known fields. */
385 if (*eax > 0x80000008)
386 *eax = 0x80000008;
387 break;
388 }
389}
390
391/* Intel has four control registers, imaginatively named cr0, cr2, cr3 and cr4.
392 * I assume there's a cr1, but it hasn't bothered us yet, so we'll not bother
393 * it. The Host needs to know when the Guest wants to change them, so we have
394 * a whole series of functions like read_cr0() and write_cr0().
395 *
396 * We start with CR0. CR0 allows you to turn on and off all kinds of basic
397 * features, but Linux only really cares about one: the horrifically-named Task
398 * Switched (TS) bit at bit 3 (ie. 8)
399 *
400 * What does the TS bit do? Well, it causes the CPU to trap (interrupt 7) if
401 * the floating point unit is used. Which allows us to restore FPU state
402 * lazily after a task switch, and Linux uses that gratefully, but wouldn't a
403 * name like "FPUTRAP bit" be a little less cryptic?
404 *
405 * We store cr0 (and cr3) locally, because the Host never changes it. The
406 * Guest sometimes wants to read it and we'd prefer not to bother the Host
407 * unnecessarily. */
408static unsigned long current_cr0, current_cr3;
409static void lguest_write_cr0(unsigned long val)
410{
411 /* 8 == TS bit. */
412 lazy_hcall(LHCALL_TS, val & 8, 0, 0);
413 current_cr0 = val;
414}
415
416static unsigned long lguest_read_cr0(void)
417{
418 return current_cr0;
419}
420
421/* Intel provided a special instruction to clear the TS bit for people too cool
422 * to use write_cr0() to do it. This "clts" instruction is faster, because all
423 * the vowels have been optimized out. */
424static void lguest_clts(void)
425{
426 lazy_hcall(LHCALL_TS, 0, 0, 0);
427 current_cr0 &= ~8U;
428}
429
430/* CR2 is the virtual address of the last page fault, which the Guest only ever
431 * reads. The Host kindly writes this into our "struct lguest_data", so we
432 * just read it out of there. */
433static unsigned long lguest_read_cr2(void)
434{
435 return lguest_data.cr2;
436}
437
438/* CR3 is the current toplevel pagetable page: the principle is the same as
439 * cr0. Keep a local copy, and tell the Host when it changes. */
440static void lguest_write_cr3(unsigned long cr3)
441{
442 lazy_hcall(LHCALL_NEW_PGTABLE, cr3, 0, 0);
443 current_cr3 = cr3;
444}
445
446static unsigned long lguest_read_cr3(void)
447{
448 return current_cr3;
449}
450
451/* CR4 is used to enable and disable PGE, but we don't care. */
452static unsigned long lguest_read_cr4(void)
453{
454 return 0;
455}
456
457static void lguest_write_cr4(unsigned long val)
458{
459}
460
461/*
462 * Page Table Handling.
463 *
464 * Now would be a good time to take a rest and grab a coffee or similarly
465 * relaxing stimulant. The easy parts are behind us, and the trek gradually
466 * winds uphill from here.
467 *
468 * Quick refresher: memory is divided into "pages" of 4096 bytes each. The CPU
469 * maps virtual addresses to physical addresses using "page tables". We could
470 * use one huge index of 1 million entries: each address is 4 bytes, so that's
471 * 1024 pages just to hold the page tables. But since most virtual addresses
472 * are unused, we use a two level index which saves space. The CR3 register
473 * contains the physical address of the top level "page directory" page, which
474 * contains physical addresses of up to 1024 second-level pages. Each of these
475 * second level pages contains up to 1024 physical addresses of actual pages,
476 * or Page Table Entries (PTEs).
477 *
478 * Here's a diagram, where arrows indicate physical addresses:
479 *
480 * CR3 ---> +---------+
481 * | --------->+---------+
482 * | | | PADDR1 |
483 * Top-level | | PADDR2 |
484 * (PMD) page | | |
485 * | | Lower-level |
486 * | | (PTE) page |
487 * | | | |
488 * .... ....
489 *
490 * So to convert a virtual address to a physical address, we look up the top
491 * level, which points us to the second level, which gives us the physical
492 * address of that page. If the top level entry was not present, or the second
493 * level entry was not present, then the virtual address is invalid (we
494 * say "the page was not mapped").
495 *
496 * Put another way, a 32-bit virtual address is divided up like so:
497 *
498 * 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
499 * |<---- 10 bits ---->|<---- 10 bits ---->|<------ 12 bits ------>|
500 * Index into top Index into second Offset within page
501 * page directory page pagetable page
502 *
503 * The kernel spends a lot of time changing both the top-level page directory
504 * and lower-level pagetable pages. The Guest doesn't know physical addresses,
505 * so while it maintains these page tables exactly like normal, it also needs
506 * to keep the Host informed whenever it makes a change: the Host will create
507 * the real page tables based on the Guests'.
508 */
509
510/* The Guest calls this to set a second-level entry (pte), ie. to map a page
511 * into a process' address space. We set the entry then tell the Host the
512 * toplevel and address this corresponds to. The Guest uses one pagetable per
513 * process, so we need to tell the Host which one we're changing (mm->pgd). */
514static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr,
515 pte_t *ptep, pte_t pteval)
516{
517 *ptep = pteval;
518 lazy_hcall(LHCALL_SET_PTE, __pa(mm->pgd), addr, pteval.pte_low);
519}
520
521/* The Guest calls this to set a top-level entry. Again, we set the entry then
522 * tell the Host which top-level page we changed, and the index of the entry we
523 * changed. */
524static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval)
525{
526 *pmdp = pmdval;
527 lazy_hcall(LHCALL_SET_PMD, __pa(pmdp)&PAGE_MASK,
528 (__pa(pmdp)&(PAGE_SIZE-1))/4, 0);
529}
530
531/* There are a couple of legacy places where the kernel sets a PTE, but we
532 * don't know the top level any more. This is useless for us, since we don't
533 * know which pagetable is changing or what address, so we just tell the Host
534 * to forget all of them. Fortunately, this is very rare.
535 *
536 * ... except in early boot when the kernel sets up the initial pagetables,
537 * which makes booting astonishingly slow. So we don't even tell the Host
538 * anything changed until we've done the first page table switch.
539 */
540static void lguest_set_pte(pte_t *ptep, pte_t pteval)
541{
542 *ptep = pteval;
543 /* Don't bother with hypercall before initial setup. */
544 if (current_cr3)
545 lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
546}
547
548/* Unfortunately for Lguest, the pv_mmu_ops for page tables were based on
549 * native page table operations. On native hardware you can set a new page
550 * table entry whenever you want, but if you want to remove one you have to do
551 * a TLB flush (a TLB is a little cache of page table entries kept by the CPU).
552 *
553 * So the lguest_set_pte_at() and lguest_set_pmd() functions above are only
554 * called when a valid entry is written, not when it's removed (ie. marked not
555 * present). Instead, this is where we come when the Guest wants to remove a
556 * page table entry: we tell the Host to set that entry to 0 (ie. the present
557 * bit is zero). */
558static void lguest_flush_tlb_single(unsigned long addr)
559{
560 /* Simply set it to zero: if it was not, it will fault back in. */
561 lazy_hcall(LHCALL_SET_PTE, current_cr3, addr, 0);
562}
563
564/* This is what happens after the Guest has removed a large number of entries.
565 * This tells the Host that any of the page table entries for userspace might
566 * have changed, ie. virtual addresses below PAGE_OFFSET. */
567static void lguest_flush_tlb_user(void)
568{
569 lazy_hcall(LHCALL_FLUSH_TLB, 0, 0, 0);
570}
571
572/* This is called when the kernel page tables have changed. That's not very
573 * common (unless the Guest is using highmem, which makes the Guest extremely
574 * slow), so it's worth separating this from the user flushing above. */
575static void lguest_flush_tlb_kernel(void)
576{
577 lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
578}
579
580/*
581 * The Unadvanced Programmable Interrupt Controller.
582 *
583 * This is an attempt to implement the simplest possible interrupt controller.
584 * I spent some time looking though routines like set_irq_chip_and_handler,
585 * set_irq_chip_and_handler_name, set_irq_chip_data and set_phasers_to_stun and
586 * I *think* this is as simple as it gets.
587 *
588 * We can tell the Host what interrupts we want blocked ready for using the
589 * lguest_data.interrupts bitmap, so disabling (aka "masking") them is as
590 * simple as setting a bit. We don't actually "ack" interrupts as such, we
591 * just mask and unmask them. I wonder if we should be cleverer?
592 */
593static void disable_lguest_irq(unsigned int irq)
594{
595 set_bit(irq, lguest_data.blocked_interrupts);
596}
597
598static void enable_lguest_irq(unsigned int irq)
599{
600 clear_bit(irq, lguest_data.blocked_interrupts);
601}
602
603/* This structure describes the lguest IRQ controller. */
604static struct irq_chip lguest_irq_controller = {
605 .name = "lguest",
606 .mask = disable_lguest_irq,
607 .mask_ack = disable_lguest_irq,
608 .unmask = enable_lguest_irq,
609};
610
611/* This sets up the Interrupt Descriptor Table (IDT) entry for each hardware
612 * interrupt (except 128, which is used for system calls), and then tells the
613 * Linux infrastructure that each interrupt is controlled by our level-based
614 * lguest interrupt controller. */
615static void __init lguest_init_IRQ(void)
616{
617 unsigned int i;
618
619 for (i = 0; i < LGUEST_IRQS; i++) {
620 int vector = FIRST_EXTERNAL_VECTOR + i;
621 if (vector != SYSCALL_VECTOR) {
622 set_intr_gate(vector, interrupt[i]);
623 set_irq_chip_and_handler(i, &lguest_irq_controller,
624 handle_level_irq);
625 }
626 }
627 /* This call is required to set up for 4k stacks, where we have
628 * separate stacks for hard and soft interrupts. */
629 irq_ctx_init(smp_processor_id());
630}
631
632/*
633 * Time.
634 *
635 * It would be far better for everyone if the Guest had its own clock, but
636 * until then the Host gives us the time on every interrupt.
637 */
638static unsigned long lguest_get_wallclock(void)
639{
640 return lguest_data.time.tv_sec;
641}
642
643static cycle_t lguest_clock_read(void)
644{
645 unsigned long sec, nsec;
646
647 /* If the Host tells the TSC speed, we can trust that. */
648 if (lguest_data.tsc_khz)
649 return native_read_tsc();
650
651 /* If we can't use the TSC, we read the time value written by the Host.
652 * Since it's in two parts (seconds and nanoseconds), we risk reading
653 * it just as it's changing from 99 & 0.999999999 to 100 and 0, and
654 * getting 99 and 0. As Linux tends to come apart under the stress of
655 * time travel, we must be careful: */
656 do {
657 /* First we read the seconds part. */
658 sec = lguest_data.time.tv_sec;
659 /* This read memory barrier tells the compiler and the CPU that
660 * this can't be reordered: we have to complete the above
661 * before going on. */
662 rmb();
663 /* Now we read the nanoseconds part. */
664 nsec = lguest_data.time.tv_nsec;
665 /* Make sure we've done that. */
666 rmb();
667 /* Now if the seconds part has changed, try again. */
668 } while (unlikely(lguest_data.time.tv_sec != sec));
669
670 /* Our non-TSC clock is in real nanoseconds. */
671 return sec*1000000000ULL + nsec;
672}
673
674/* This is what we tell the kernel is our clocksource. */
675static struct clocksource lguest_clock = {
676 .name = "lguest",
677 .rating = 400,
678 .read = lguest_clock_read,
679 .mask = CLOCKSOURCE_MASK(64),
680 .mult = 1 << 22,
681 .shift = 22,
682 .flags = CLOCK_SOURCE_IS_CONTINUOUS,
683};
684
685/* The "scheduler clock" is just our real clock, adjusted to start at zero */
686static unsigned long long lguest_sched_clock(void)
687{
688 return cyc2ns(&lguest_clock, lguest_clock_read() - clock_base);
689}
690
691/* We also need a "struct clock_event_device": Linux asks us to set it to go
692 * off some time in the future. Actually, James Morris figured all this out, I
693 * just applied the patch. */
694static int lguest_clockevent_set_next_event(unsigned long delta,
695 struct clock_event_device *evt)
696{
697 if (delta < LG_CLOCK_MIN_DELTA) {
698 if (printk_ratelimit())
699 printk(KERN_DEBUG "%s: small delta %lu ns\n",
700 __FUNCTION__, delta);
701 return -ETIME;
702 }
703 hcall(LHCALL_SET_CLOCKEVENT, delta, 0, 0);
704 return 0;
705}
706
707static void lguest_clockevent_set_mode(enum clock_event_mode mode,
708 struct clock_event_device *evt)
709{
710 switch (mode) {
711 case CLOCK_EVT_MODE_UNUSED:
712 case CLOCK_EVT_MODE_SHUTDOWN:
713 /* A 0 argument shuts the clock down. */
714 hcall(LHCALL_SET_CLOCKEVENT, 0, 0, 0);
715 break;
716 case CLOCK_EVT_MODE_ONESHOT:
717 /* This is what we expect. */
718 break;
719 case CLOCK_EVT_MODE_PERIODIC:
720 BUG();
721 case CLOCK_EVT_MODE_RESUME:
722 break;
723 }
724}
725
726/* This describes our primitive timer chip. */
727static struct clock_event_device lguest_clockevent = {
728 .name = "lguest",
729 .features = CLOCK_EVT_FEAT_ONESHOT,
730 .set_next_event = lguest_clockevent_set_next_event,
731 .set_mode = lguest_clockevent_set_mode,
732 .rating = INT_MAX,
733 .mult = 1,
734 .shift = 0,
735 .min_delta_ns = LG_CLOCK_MIN_DELTA,
736 .max_delta_ns = LG_CLOCK_MAX_DELTA,
737};
738
739/* This is the Guest timer interrupt handler (hardware interrupt 0). We just
740 * call the clockevent infrastructure and it does whatever needs doing. */
741static void lguest_time_irq(unsigned int irq, struct irq_desc *desc)
742{
743 unsigned long flags;
744
745 /* Don't interrupt us while this is running. */
746 local_irq_save(flags);
747 lguest_clockevent.event_handler(&lguest_clockevent);
748 local_irq_restore(flags);
749}
750
751/* At some point in the boot process, we get asked to set up our timing
752 * infrastructure. The kernel doesn't expect timer interrupts before this, but
753 * we cleverly initialized the "blocked_interrupts" field of "struct
754 * lguest_data" so that timer interrupts were blocked until now. */
755static void lguest_time_init(void)
756{
757 /* Set up the timer interrupt (0) to go to our simple timer routine */
758 set_irq_handler(0, lguest_time_irq);
759
760 /* Our clock structure look like arch/i386/kernel/tsc.c if we can use
761 * the TSC, otherwise it's a dumb nanosecond-resolution clock. Either
762 * way, the "rating" is initialized so high that it's always chosen
763 * over any other clocksource. */
764 if (lguest_data.tsc_khz)
765 lguest_clock.mult = clocksource_khz2mult(lguest_data.tsc_khz,
766 lguest_clock.shift);
767 clock_base = lguest_clock_read();
768 clocksource_register(&lguest_clock);
769
770 /* Now we've set up our clock, we can use it as the scheduler clock */
771 pv_time_ops.sched_clock = lguest_sched_clock;
772
773 /* We can't set cpumask in the initializer: damn C limitations! Set it
774 * here and register our timer device. */
775 lguest_clockevent.cpumask = cpumask_of_cpu(0);
776 clockevents_register_device(&lguest_clockevent);
777
778 /* Finally, we unblock the timer interrupt. */
779 enable_lguest_irq(0);
780}
781
782/*
783 * Miscellaneous bits and pieces.
784 *
785 * Here is an oddball collection of functions which the Guest needs for things
786 * to work. They're pretty simple.
787 */
788
789/* The Guest needs to tell the host what stack it expects traps to use. For
790 * native hardware, this is part of the Task State Segment mentioned above in
791 * lguest_load_tr_desc(), but to help hypervisors there's this special call.
792 *
793 * We tell the Host the segment we want to use (__KERNEL_DS is the kernel data
794 * segment), the privilege level (we're privilege level 1, the Host is 0 and
795 * will not tolerate us trying to use that), the stack pointer, and the number
796 * of pages in the stack. */
797static void lguest_load_esp0(struct tss_struct *tss,
798 struct thread_struct *thread)
799{
800 lazy_hcall(LHCALL_SET_STACK, __KERNEL_DS|0x1, thread->esp0,
801 THREAD_SIZE/PAGE_SIZE);
802}
803
804/* Let's just say, I wouldn't do debugging under a Guest. */
805static void lguest_set_debugreg(int regno, unsigned long value)
806{
807 /* FIXME: Implement */
808}
809
810/* There are times when the kernel wants to make sure that no memory writes are
811 * caught in the cache (that they've all reached real hardware devices). This
812 * doesn't matter for the Guest which has virtual hardware.
813 *
814 * On the Pentium 4 and above, cpuid() indicates that the Cache Line Flush
815 * (clflush) instruction is available and the kernel uses that. Otherwise, it
816 * uses the older "Write Back and Invalidate Cache" (wbinvd) instruction.
817 * Unlike clflush, wbinvd can only be run at privilege level 0. So we can
818 * ignore clflush, but replace wbinvd.
819 */
820static void lguest_wbinvd(void)
821{
822}
823
824/* If the Guest expects to have an Advanced Programmable Interrupt Controller,
825 * we play dumb by ignoring writes and returning 0 for reads. So it's no
826 * longer Programmable nor Controlling anything, and I don't think 8 lines of
827 * code qualifies for Advanced. It will also never interrupt anything. It
828 * does, however, allow us to get through the Linux boot code. */
829#ifdef CONFIG_X86_LOCAL_APIC
830static void lguest_apic_write(unsigned long reg, unsigned long v)
831{
832}
833
834static unsigned long lguest_apic_read(unsigned long reg)
835{
836 return 0;
837}
838#endif
839
840/* STOP! Until an interrupt comes in. */
841static void lguest_safe_halt(void)
842{
843 hcall(LHCALL_HALT, 0, 0, 0);
844}
845
846/* Perhaps CRASH isn't the best name for this hypercall, but we use it to get a
847 * message out when we're crashing as well as elegant termination like powering
848 * off.
849 *
850 * Note that the Host always prefers that the Guest speak in physical addresses
851 * rather than virtual addresses, so we use __pa() here. */
852static void lguest_power_off(void)
853{
854 hcall(LHCALL_CRASH, __pa("Power down"), 0, 0);
855}
856
857/*
858 * Panicing.
859 *
860 * Don't. But if you did, this is what happens.
861 */
862static int lguest_panic(struct notifier_block *nb, unsigned long l, void *p)
863{
864 hcall(LHCALL_CRASH, __pa(p), 0, 0);
865 /* The hcall won't return, but to keep gcc happy, we're "done". */
866 return NOTIFY_DONE;
867}
868
869static struct notifier_block paniced = {
870 .notifier_call = lguest_panic
871};
872
873/* Setting up memory is fairly easy. */
874static __init char *lguest_memory_setup(void)
875{
876 /* We do this here and not earlier because lockcheck barfs if we do it
877 * before start_kernel() */
878 atomic_notifier_chain_register(&panic_notifier_list, &paniced);
879
880 /* The Linux bootloader header contains an "e820" memory map: the
881 * Launcher populated the first entry with our memory limit. */
882 add_memory_region(boot_params.e820_map[0].addr,
883 boot_params.e820_map[0].size,
884 boot_params.e820_map[0].type);
885
886 /* This string is for the boot messages. */
887 return "LGUEST";
888}
889
890/*G:050
891 * Patching (Powerfully Placating Performance Pedants)
892 *
893 * We have already seen that pv_ops structures let us replace simple
894 * native instructions with calls to the appropriate back end all throughout
895 * the kernel. This allows the same kernel to run as a Guest and as a native
896 * kernel, but it's slow because of all the indirect branches.
897 *
898 * Remember that David Wheeler quote about "Any problem in computer science can
899 * be solved with another layer of indirection"? The rest of that quote is
900 * "... But that usually will create another problem." This is the first of
901 * those problems.
902 *
903 * Our current solution is to allow the paravirt back end to optionally patch
904 * over the indirect calls to replace them with something more efficient. We
905 * patch the four most commonly called functions: disable interrupts, enable
906 * interrupts, restore interrupts and save interrupts. We usually have 10
907 * bytes to patch into: the Guest versions of these operations are small enough
908 * that we can fit comfortably.
909 *
910 * First we need assembly templates of each of the patchable Guest operations,
911 * and these are in lguest_asm.S. */
912
913/*G:060 We construct a table from the assembler templates: */
914static const struct lguest_insns
915{
916 const char *start, *end;
917} lguest_insns[] = {
918 [PARAVIRT_PATCH(pv_irq_ops.irq_disable)] = { lgstart_cli, lgend_cli },
919 [PARAVIRT_PATCH(pv_irq_ops.irq_enable)] = { lgstart_sti, lgend_sti },
920 [PARAVIRT_PATCH(pv_irq_ops.restore_fl)] = { lgstart_popf, lgend_popf },
921 [PARAVIRT_PATCH(pv_irq_ops.save_fl)] = { lgstart_pushf, lgend_pushf },
922};
923
924/* Now our patch routine is fairly simple (based on the native one in
925 * paravirt.c). If we have a replacement, we copy it in and return how much of
926 * the available space we used. */
927static unsigned lguest_patch(u8 type, u16 clobber, void *ibuf,
928 unsigned long addr, unsigned len)
929{
930 unsigned int insn_len;
931
932 /* Don't do anything special if we don't have a replacement */
933 if (type >= ARRAY_SIZE(lguest_insns) || !lguest_insns[type].start)
934 return paravirt_patch_default(type, clobber, ibuf, addr, len);
935
936 insn_len = lguest_insns[type].end - lguest_insns[type].start;
937
938 /* Similarly if we can't fit replacement (shouldn't happen, but let's
939 * be thorough). */
940 if (len < insn_len)
941 return paravirt_patch_default(type, clobber, ibuf, addr, len);
942
943 /* Copy in our instructions. */
944 memcpy(ibuf, lguest_insns[type].start, insn_len);
945 return insn_len;
946}
947
948/*G:030 Once we get to lguest_init(), we know we're a Guest. The pv_ops
949 * structures in the kernel provide points for (almost) every routine we have
950 * to override to avoid privileged instructions. */
951__init void lguest_init(void *boot)
952{
953 /* Copy boot parameters first: the Launcher put the physical location
954 * in %esi, and head.S converted that to a virtual address and handed
955 * it to us. We use "__memcpy" because "memcpy" sometimes tries to do
956 * tricky things to go faster, and we're not ready for that. */
957 __memcpy(&boot_params, boot, PARAM_SIZE);
958 /* The boot parameters also tell us where the command-line is: save
959 * that, too. */
960 __memcpy(boot_command_line, __va(boot_params.hdr.cmd_line_ptr),
961 COMMAND_LINE_SIZE);
962
963 /* We're under lguest, paravirt is enabled, and we're running at
964 * privilege level 1, not 0 as normal. */
965 pv_info.name = "lguest";
966 pv_info.paravirt_enabled = 1;
967 pv_info.kernel_rpl = 1;
968
969 /* We set up all the lguest overrides for sensitive operations. These
970 * are detailed with the operations themselves. */
971
972 /* interrupt-related operations */
973 pv_irq_ops.init_IRQ = lguest_init_IRQ;
974 pv_irq_ops.save_fl = save_fl;
975 pv_irq_ops.restore_fl = restore_fl;
976 pv_irq_ops.irq_disable = irq_disable;
977 pv_irq_ops.irq_enable = irq_enable;
978 pv_irq_ops.safe_halt = lguest_safe_halt;
979
980 /* init-time operations */
981 pv_init_ops.memory_setup = lguest_memory_setup;
982 pv_init_ops.patch = lguest_patch;
983
984 /* Intercepts of various cpu instructions */
985 pv_cpu_ops.load_gdt = lguest_load_gdt;
986 pv_cpu_ops.cpuid = lguest_cpuid;
987 pv_cpu_ops.load_idt = lguest_load_idt;
988 pv_cpu_ops.iret = lguest_iret;
989 pv_cpu_ops.load_esp0 = lguest_load_esp0;
990 pv_cpu_ops.load_tr_desc = lguest_load_tr_desc;
991 pv_cpu_ops.set_ldt = lguest_set_ldt;
992 pv_cpu_ops.load_tls = lguest_load_tls;
993 pv_cpu_ops.set_debugreg = lguest_set_debugreg;
994 pv_cpu_ops.clts = lguest_clts;
995 pv_cpu_ops.read_cr0 = lguest_read_cr0;
996 pv_cpu_ops.write_cr0 = lguest_write_cr0;
997 pv_cpu_ops.read_cr4 = lguest_read_cr4;
998 pv_cpu_ops.write_cr4 = lguest_write_cr4;
999 pv_cpu_ops.write_gdt_entry = lguest_write_gdt_entry;
1000 pv_cpu_ops.write_idt_entry = lguest_write_idt_entry;
1001 pv_cpu_ops.wbinvd = lguest_wbinvd;
1002 pv_cpu_ops.lazy_mode.enter = paravirt_enter_lazy_cpu;
1003 pv_cpu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
1004
1005 /* pagetable management */
1006 pv_mmu_ops.write_cr3 = lguest_write_cr3;
1007 pv_mmu_ops.flush_tlb_user = lguest_flush_tlb_user;
1008 pv_mmu_ops.flush_tlb_single = lguest_flush_tlb_single;
1009 pv_mmu_ops.flush_tlb_kernel = lguest_flush_tlb_kernel;
1010 pv_mmu_ops.set_pte = lguest_set_pte;
1011 pv_mmu_ops.set_pte_at = lguest_set_pte_at;
1012 pv_mmu_ops.set_pmd = lguest_set_pmd;
1013 pv_mmu_ops.read_cr2 = lguest_read_cr2;
1014 pv_mmu_ops.read_cr3 = lguest_read_cr3;
1015 pv_mmu_ops.lazy_mode.enter = paravirt_enter_lazy_mmu;
1016 pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
1017
1018#ifdef CONFIG_X86_LOCAL_APIC
1019 /* apic read/write intercepts */
1020 pv_apic_ops.apic_write = lguest_apic_write;
1021 pv_apic_ops.apic_write_atomic = lguest_apic_write;
1022 pv_apic_ops.apic_read = lguest_apic_read;
1023#endif
1024
1025 /* time operations */
1026 pv_time_ops.get_wallclock = lguest_get_wallclock;
1027 pv_time_ops.time_init = lguest_time_init;
1028
1029 /* Now is a good time to look at the implementations of these functions
1030 * before returning to the rest of lguest_init(). */
1031
1032 /*G:070 Now we've seen all the paravirt_ops, we return to
1033 * lguest_init() where the rest of the fairly chaotic boot setup
1034 * occurs.
1035 *
1036 * The Host expects our first hypercall to tell it where our "struct
1037 * lguest_data" is, so we do that first. */
1038 hcall(LHCALL_LGUEST_INIT, __pa(&lguest_data), 0, 0);
1039
1040 /* The native boot code sets up initial page tables immediately after
1041 * the kernel itself, and sets init_pg_tables_end so they're not
1042 * clobbered. The Launcher places our initial pagetables somewhere at
1043 * the top of our physical memory, so we don't need extra space: set
1044 * init_pg_tables_end to the end of the kernel. */
1045 init_pg_tables_end = __pa(pg0);
1046
1047 /* Load the %fs segment register (the per-cpu segment register) with
1048 * the normal data segment to get through booting. */
1049 asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_DS) : "memory");
1050
1051 /* Clear the part of the kernel data which is expected to be zero.
1052 * Normally it will be anyway, but if we're loading from a bzImage with
1053 * CONFIG_RELOCATALE=y, the relocations will be sitting here. */
1054 memset(__bss_start, 0, __bss_stop - __bss_start);
1055
1056 /* The Host uses the top of the Guest's virtual address space for the
1057 * Host<->Guest Switcher, and it tells us how much it needs in
1058 * lguest_data.reserve_mem, set up on the LGUEST_INIT hypercall. */
1059 reserve_top_address(lguest_data.reserve_mem);
1060
1061 /* If we don't initialize the lock dependency checker now, it crashes
1062 * paravirt_disable_iospace. */
1063 lockdep_init();
1064
1065 /* The IDE code spends about 3 seconds probing for disks: if we reserve
1066 * all the I/O ports up front it can't get them and so doesn't probe.
1067 * Other device drivers are similar (but less severe). This cuts the
1068 * kernel boot time on my machine from 4.1 seconds to 0.45 seconds. */
1069 paravirt_disable_iospace();
1070
1071 /* This is messy CPU setup stuff which the native boot code does before
1072 * start_kernel, so we have to do, too: */
1073 cpu_detect(&new_cpu_data);
1074 /* head.S usually sets up the first capability word, so do it here. */
1075 new_cpu_data.x86_capability[0] = cpuid_edx(1);
1076
1077 /* Math is always hard! */
1078 new_cpu_data.hard_math = 1;
1079
1080#ifdef CONFIG_X86_MCE
1081 mce_disabled = 1;
1082#endif
1083#ifdef CONFIG_ACPI
1084 acpi_disabled = 1;
1085 acpi_ht = 0;
1086#endif
1087
1088 /* We set the perferred console to "hvc". This is the "hypervisor
1089 * virtual console" driver written by the PowerPC people, which we also
1090 * adapted for lguest's use. */
1091 add_preferred_console("hvc", 0, NULL);
1092
1093 /* Last of all, we set the power management poweroff hook to point to
1094 * the Guest routine to power off. */
1095 pm_power_off = lguest_power_off;
1096
1097 /* Now we're set up, call start_kernel() in init/main.c and we proceed
1098 * to boot as normal. It never returns. */
1099 start_kernel();
1100}
1101/*
1102 * This marks the end of stage II of our journey, The Guest.
1103 *
1104 * It is now time for us to explore the nooks and crannies of the three Guest
1105 * devices and complete our understanding of the Guest in "make Drivers".
1106 */
diff --git a/drivers/lguest/lguest_asm.S b/drivers/lguest/lguest_asm.S
deleted file mode 100644
index 1ddcd5cd20f6..000000000000
--- a/drivers/lguest/lguest_asm.S
+++ /dev/null
@@ -1,93 +0,0 @@
1#include <linux/linkage.h>
2#include <linux/lguest.h>
3#include <asm/asm-offsets.h>
4#include <asm/thread_info.h>
5#include <asm/processor-flags.h>
6
7/*G:020 This is where we begin: we have a magic signature which the launcher
8 * looks for. The plan is that the Linux boot protocol will be extended with a
9 * "platform type" field which will guide us here from the normal entry point,
10 * but for the moment this suffices. The normal boot code uses %esi for the
11 * boot header, so we do too. We convert it to a virtual address by adding
12 * PAGE_OFFSET, and hand it to lguest_init() as its argument (ie. %eax).
13 *
14 * The .section line puts this code in .init.text so it will be discarded after
15 * boot. */
16.section .init.text, "ax", @progbits
17.ascii "GenuineLguest"
18 /* Set up initial stack. */
19 movl $(init_thread_union+THREAD_SIZE),%esp
20 movl %esi, %eax
21 addl $__PAGE_OFFSET, %eax
22 jmp lguest_init
23
24/*G:055 We create a macro which puts the assembler code between lgstart_ and
25 * lgend_ markers. These templates are put in the .text section: they can't be
26 * discarded after boot as we may need to patch modules, too. */
27.text
28#define LGUEST_PATCH(name, insns...) \
29 lgstart_##name: insns; lgend_##name:; \
30 .globl lgstart_##name; .globl lgend_##name
31
32LGUEST_PATCH(cli, movl $0, lguest_data+LGUEST_DATA_irq_enabled)
33LGUEST_PATCH(sti, movl $X86_EFLAGS_IF, lguest_data+LGUEST_DATA_irq_enabled)
34LGUEST_PATCH(popf, movl %eax, lguest_data+LGUEST_DATA_irq_enabled)
35LGUEST_PATCH(pushf, movl lguest_data+LGUEST_DATA_irq_enabled, %eax)
36/*:*/
37
38/* These demark the EIP range where host should never deliver interrupts. */
39.global lguest_noirq_start
40.global lguest_noirq_end
41
42/*M:004 When the Host reflects a trap or injects an interrupt into the Guest,
43 * it sets the eflags interrupt bit on the stack based on
44 * lguest_data.irq_enabled, so the Guest iret logic does the right thing when
45 * restoring it. However, when the Host sets the Guest up for direct traps,
46 * such as system calls, the processor is the one to push eflags onto the
47 * stack, and the interrupt bit will be 1 (in reality, interrupts are always
48 * enabled in the Guest).
49 *
50 * This turns out to be harmless: the only trap which should happen under Linux
51 * with interrupts disabled is Page Fault (due to our lazy mapping of vmalloc
52 * regions), which has to be reflected through the Host anyway. If another
53 * trap *does* go off when interrupts are disabled, the Guest will panic, and
54 * we'll never get to this iret! :*/
55
56/*G:045 There is one final paravirt_op that the Guest implements, and glancing
57 * at it you can see why I left it to last. It's *cool*! It's in *assembler*!
58 *
59 * The "iret" instruction is used to return from an interrupt or trap. The
60 * stack looks like this:
61 * old address
62 * old code segment & privilege level
63 * old processor flags ("eflags")
64 *
65 * The "iret" instruction pops those values off the stack and restores them all
66 * at once. The only problem is that eflags includes the Interrupt Flag which
67 * the Guest can't change: the CPU will simply ignore it when we do an "iret".
68 * So we have to copy eflags from the stack to lguest_data.irq_enabled before
69 * we do the "iret".
70 *
71 * There are two problems with this: firstly, we need to use a register to do
72 * the copy and secondly, the whole thing needs to be atomic. The first
73 * problem is easy to solve: push %eax on the stack so we can use it, and then
74 * restore it at the end just before the real "iret".
75 *
76 * The second is harder: copying eflags to lguest_data.irq_enabled will turn
77 * interrupts on before we're finished, so we could be interrupted before we
78 * return to userspace or wherever. Our solution to this is to surround the
79 * code with lguest_noirq_start: and lguest_noirq_end: labels. We tell the
80 * Host that it is *never* to interrupt us there, even if interrupts seem to be
81 * enabled. */
82ENTRY(lguest_iret)
83 pushl %eax
84 movl 12(%esp), %eax
85lguest_noirq_start:
86 /* Note the %ss: segment prefix here. Normal data accesses use the
87 * "ds" segment, but that will have already been restored for whatever
88 * we're returning to (such as userspace): we can't trust it. The %ss:
89 * prefix makes sure we use the stack segment, which is still valid. */
90 movl %eax,%ss:lguest_data+LGUEST_DATA_irq_enabled
91 popl %eax
92 iret
93lguest_noirq_end:
generated by cgit v1.2.2 (git 2.25.0) at 2024-11-28 02:16:34 -0500