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authorRusty Russell <rusty@rustcorp.com.au>2007-07-26 13:41:05 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-26 14:35:17 -0400
commitf56a384e98aa81065038c4e16f39ed989ccae687 (patch)
tree923bcaabd76a88351fe5e61370143350747a90c4 /drivers/lguest
parentf8f0fdcd40449d318f8dc30c1b361b0b7f54134a (diff)
lguest: documentation VII: FIXMEs
Documentation: The FIXMEs Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/lguest')
-rw-r--r--drivers/lguest/interrupts_and_traps.c14
-rw-r--r--drivers/lguest/io.c10
-rw-r--r--drivers/lguest/lguest.c8
-rw-r--r--drivers/lguest/lguest_asm.S14
-rw-r--r--drivers/lguest/page_tables.c5
-rw-r--r--drivers/lguest/segments.c4
6 files changed, 55 insertions, 0 deletions
diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index 3d9830322646..bd0091bf79ec 100644
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -231,6 +231,20 @@ static int direct_trap(const struct lguest *lg,
231 * go direct, of course 8) */ 231 * go direct, of course 8) */
232 return idt_type(trap->a, trap->b) == 0xF; 232 return idt_type(trap->a, trap->b) == 0xF;
233} 233}
234/*:*/
235
236/*M:005 The Guest has the ability to turn its interrupt gates into trap gates,
237 * if it is careful. The Host will let trap gates can go directly to the
238 * Guest, but the Guest needs the interrupts atomically disabled for an
239 * interrupt gate. It can do this by pointing the trap gate at instructions
240 * within noirq_start and noirq_end, where it can safely disable interrupts. */
241
242/*M:006 The Guests do not use the sysenter (fast system call) instruction,
243 * because it's hardcoded to enter privilege level 0 and so can't go direct.
244 * It's about twice as fast as the older "int 0x80" system call, so it might
245 * still be worthwhile to handle it in the Switcher and lcall down to the
246 * Guest. The sysenter semantics are hairy tho: search for that keyword in
247 * entry.S :*/
234 248
235/*H:260 When we make traps go directly into the Guest, we need to make sure 249/*H:260 When we make traps go directly into the Guest, we need to make sure
236 * the kernel stack is valid (ie. mapped in the page tables). Otherwise, the 250 * the kernel stack is valid (ie. mapped in the page tables). Otherwise, the
diff --git a/drivers/lguest/io.c b/drivers/lguest/io.c
index da288128e44f..ea68613b43f6 100644
--- a/drivers/lguest/io.c
+++ b/drivers/lguest/io.c
@@ -553,6 +553,16 @@ void release_all_dma(struct lguest *lg)
553 up_read(&lg->mm->mmap_sem); 553 up_read(&lg->mm->mmap_sem);
554} 554}
555 555
556/*M:007 We only return a single DMA buffer to the Launcher, but it would be
557 * more efficient to return a pointer to the entire array of DMA buffers, which
558 * it can cache and choose one whenever it wants.
559 *
560 * Currently the Launcher uses a write to /dev/lguest, and the return value is
561 * the address of the DMA structure with the interrupt number placed in
562 * dma->used_len. If we wanted to return the entire array, we need to return
563 * the address, array size and interrupt number: this seems to require an
564 * ioctl(). :*/
565
556/*L:320 This routine looks for a DMA buffer registered by the Guest on the 566/*L:320 This routine looks for a DMA buffer registered by the Guest on the
557 * given key (using the BIND_DMA hypercall). */ 567 * given key (using the BIND_DMA hypercall). */
558unsigned long get_dma_buffer(struct lguest *lg, 568unsigned long get_dma_buffer(struct lguest *lg,
diff --git a/drivers/lguest/lguest.c b/drivers/lguest/lguest.c
index 7e7e9fb3aefd..6dfe568523a2 100644
--- a/drivers/lguest/lguest.c
+++ b/drivers/lguest/lguest.c
@@ -250,6 +250,14 @@ static void irq_enable(void)
250{ 250{
251 lguest_data.irq_enabled = X86_EFLAGS_IF; 251 lguest_data.irq_enabled = X86_EFLAGS_IF;
252} 252}
253/*:*/
254/*M:003 Note that we don't check for outstanding interrupts when we re-enable
255 * them (or when we unmask an interrupt). This seems to work for the moment,
256 * since interrupts are rare and we'll just get the interrupt on the next timer
257 * tick, but when we turn on CONFIG_NO_HZ, we should revisit this. One way
258 * would be to put the "irq_enabled" field in a page by itself, and have the
259 * Host write-protect it when an interrupt comes in when irqs are disabled.
260 * There will then be a page fault as soon as interrupts are re-enabled. :*/
253 261
254/*G:034 262/*G:034
255 * The Interrupt Descriptor Table (IDT). 263 * The Interrupt Descriptor Table (IDT).
diff --git a/drivers/lguest/lguest_asm.S b/drivers/lguest/lguest_asm.S
index 3126ae923cc0..f182c6a36209 100644
--- a/drivers/lguest/lguest_asm.S
+++ b/drivers/lguest/lguest_asm.S
@@ -39,6 +39,20 @@ LGUEST_PATCH(pushf, movl lguest_data+LGUEST_DATA_irq_enabled, %eax)
39.global lguest_noirq_start 39.global lguest_noirq_start
40.global lguest_noirq_end 40.global lguest_noirq_end
41 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
42/*G:045 There is one final paravirt_op that the Guest implements, and glancing 56/*G:045 There is one final paravirt_op that the Guest implements, and glancing
43 * at it you can see why I left it to last. It's *cool*! It's in *assembler*! 57 * at it you can see why I left it to last. It's *cool*! It's in *assembler*!
44 * 58 *
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index cd047e81cd63..b7a924ace684 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -15,6 +15,11 @@
15#include <asm/tlbflush.h> 15#include <asm/tlbflush.h>
16#include "lg.h" 16#include "lg.h"
17 17
18/*M:008 We hold reference to pages, which prevents them from being swapped.
19 * It'd be nice to have a callback in the "struct mm_struct" when Linux wants
20 * to swap out. If we had this, and a shrinker callback to trim PTE pages, we
21 * could probably consider launching Guests as non-root. :*/
22
18/*H:300 23/*H:300
19 * The Page Table Code 24 * The Page Table Code
20 * 25 *
diff --git a/drivers/lguest/segments.c b/drivers/lguest/segments.c
index 4d4e5a4586f9..f675a41a80da 100644
--- a/drivers/lguest/segments.c
+++ b/drivers/lguest/segments.c
@@ -94,6 +94,10 @@ static void check_segment_use(struct lguest *lg, unsigned int desc)
94 || lg->regs->ss / 8 == desc) 94 || lg->regs->ss / 8 == desc)
95 kill_guest(lg, "Removed live GDT entry %u", desc); 95 kill_guest(lg, "Removed live GDT entry %u", desc);
96} 96}
97/*:*/
98/*M:009 We wouldn't need to check for removal of in-use segments if we handled
99 * faults in the Switcher. However, it's probably not a worthwhile
100 * optimization. :*/
97 101
98/*H:610 Once the GDT has been changed, we look through the changed entries and 102/*H:610 Once the GDT has been changed, we look through the changed entries and
99 * see if they're OK. If not, we'll call kill_guest() and the Guest will never 103 * see if they're OK. If not, we'll call kill_guest() and the Guest will never