[PATCH] paravirt: Patch inline replacements for paravirt intercepts

It turns out that the most called ops, by several orders of magnitude,
are the interrupt manipulation ops.  These are obvious candidates for
patching, so mark them up and create infrastructure for it.

The method used is that the ops structure has a patch function, which
is called for each place which needs to be patched: this returns a
number of instructions (the rest are NOP-padded).

Usually we can spare a register (%eax) for the binary patched code to
use, but in a couple of critical places in entry.S we can't: we make
the clobbers explicit at the call site, and manually clobber the
allowed registers in debug mode as an extra check.

And:

Don't abuse CONFIG_DEBUG_KERNEL, add CONFIG_DEBUG_PARAVIRT.

And:

AK:  Fix warnings in x86-64 alternative.c build

And:

AK: Fix compilation with defconfig

And:

^From: Andrew Morton <akpm@osdl.org>

Some binutlises still like to emit references to __stop_parainstructions and
__start_parainstructions.

And:

AK: Fix warnings about unused variables when PARAVIRT is disabled.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>

1 files changed, 52 insertions, 11 deletions

diff --git a/arch/i386/kernel/alternative.c b/arch/i386/kernel/alternative.c
index 535f9794fba1..9eca21b49f6b 100644
--- a/arch/i386/kernel/alternative.c
+++ b/arch/i386/kernel/alternative.c
@@ -124,6 +124,20 @@ static unsigned char** find_nop_table(void)
 
 #endif /* CONFIG_X86_64 */
 
+static void nop_out(void *insns, unsigned int len)
+{
+        unsigned char **noptable = find_nop_table();
+
+        while (len > 0) {
+                unsigned int noplen = len;
+                if (noplen > ASM_NOP_MAX)
+                        noplen = ASM_NOP_MAX;
+                memcpy(insns, noptable[noplen], noplen);
+                insns += noplen;
+                len -= noplen;
+        }
+}
+
 extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
 extern struct alt_instr __smp_alt_instructions[], __smp_alt_instructions_end[];
 extern u8 *__smp_locks[], *__smp_locks_end[];
@@ -138,10 +152,9 @@ extern u8 __smp_alt_begin[], __smp_alt_end[];
 
 void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
 {
-        unsigned char **noptable = find_nop_table();
         struct alt_instr *a;
         u8 *instr;
-        int diff, i, k;
+        int diff;
 
         DPRINTK("%s: alt table %p -> %p\n", __FUNCTION__, start, end);
         for (a = start; a < end; a++) {
@@ -159,13 +172,7 @@ void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
 #endif
                 memcpy(instr, a->replacement, a->replacementlen);
                 diff = a->instrlen - a->replacementlen;
-                /* Pad the rest with nops */
-                for (i = a->replacementlen; diff > 0; diff -= k, i += k) {
-                        k = diff;
-                        if (k > ASM_NOP_MAX)
-                                k = ASM_NOP_MAX;
-                        memcpy(a->instr + i, noptable[k], k);
-                }
+                nop_out(instr + a->replacementlen, diff);
         }
 }
 
@@ -209,7 +216,6 @@ static void alternatives_smp_lock(u8 **start, u8 **end, u8 *text, u8 *text_end)
 
 static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end)
 {
-        unsigned char **noptable = find_nop_table();
         u8 **ptr;
 
         for (ptr = start; ptr < end; ptr++) {
@@ -217,7 +223,7 @@ static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end
                         continue;
                 if (*ptr > text_end)
                         continue;
-                **ptr = noptable[1][0];
+                nop_out(*ptr, 1);
         };
 }
 
@@ -343,6 +349,40 @@ void alternatives_smp_switch(int smp)
 
 #endif
 
+#ifdef CONFIG_PARAVIRT
+void apply_paravirt(struct paravirt_patch *start, struct paravirt_patch *end)
+{
+        struct paravirt_patch *p;
+
+        for (p = start; p < end; p++) {
+                unsigned int used;
+
+                used = paravirt_ops.patch(p->instrtype, p->clobbers, p->instr,
+                                          p->len);
+#ifdef CONFIG_DEBUG_PARAVIRT
+                {
+                int i;
+                /* Deliberately clobber regs using "not %reg" to find bugs. */
+                for (i = 0; i < 3; i++) {
+                        if (p->len - used >= 2 && (p->clobbers & (1 << i))) {
+                                memcpy(p->instr + used, "\xf7\xd0", 2);
+                                p->instr[used+1] |= i;
+                                used += 2;
+                        }
+                }
+                }
+#endif
+                /* Pad the rest with nops */
+                nop_out(p->instr + used, p->len - used);
+        }
+
+        /* Sync to be conservative, in case we patched following instructions */
+        sync_core();
+}
+extern struct paravirt_patch __start_parainstructions[],
+        __stop_parainstructions[];
+#endif  /* CONFIG_PARAVIRT */
+
 void __init alternative_instructions(void)
 {
         unsigned long flags;
@@ -390,5 +430,6 @@ void __init alternative_instructions(void)
                 alternatives_smp_switch(0);
         }
 #endif
+        apply_paravirt(__start_parainstructions, __stop_parainstructions);
         local_irq_restore(flags);
 }