When the old value and new one are the same the emulator skips the
write; this is undesiderable when the destination is a MMIO area and the
write shall be performed regardless of the previous value. This
optimization breaks e.g. a Linux guest APIC compiled without
X86_GOOD_APIC.
Remove the check and always perform the writeback stage in the
emulation.
Signed-Off-By: Luca Tettamanti <[EMAIL PROTECTED]>
---
drivers/kvm/x86_emulate.c | 60 +++++++++++++++++++---------------------
1 file changed, 29 insertions(+), 31 deletions(-)
diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index a4a8481..cea9f3a 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -1057,40 +1057,38 @@ done_prefixes:
}
writeback:
- if ((d & Mov) || (dst.orig_val != dst.val)) {
- switch (dst.type) {
- case OP_REG:
- /* The 4-byte case *is* correct: in 64-bit mode we
zero-extend. */
- switch (dst.bytes) {
- case 1:
- *(u8 *)dst.ptr = (u8)dst.val;
- break;
- case 2:
- *(u16 *)dst.ptr = (u16)dst.val;
- break;
- case 4:
- *dst.ptr = (u32)dst.val;
- break; /* 64b: zero-ext */
- case 8:
- *dst.ptr = dst.val;
- break;
- }
+ switch (dst.type) {
+ case OP_REG:
+ /* The 4-byte case *is* correct: in 64-bit mode we zero-extend.
*/
+ switch (dst.bytes) {
+ case 1:
+ *(u8 *)dst.ptr = (u8)dst.val;
break;
- case OP_MEM:
- if (lock_prefix)
- rc = ops->cmpxchg_emulated((unsigned long)dst.
- ptr, &dst.orig_val,
- &dst.val, dst.bytes,
- ctxt);
- else
- rc = ops->write_emulated((unsigned long)dst.ptr,
- &dst.val, dst.bytes,
- ctxt);
- if (rc != 0)
- goto done;
- default:
+ case 2:
+ *(u16 *)dst.ptr = (u16)dst.val;
+ break;
+ case 4:
+ *dst.ptr = (u32)dst.val;
+ break; /* 64b: zero-ext */
+ case 8:
+ *dst.ptr = dst.val;
break;
}
+ break;
+ case OP_MEM:
+ if (lock_prefix)
+ rc = ops->cmpxchg_emulated((unsigned long)dst.
+ ptr, &dst.orig_val,
+ &dst.val, dst.bytes,
+ ctxt);
+ else
+ rc = ops->write_emulated((unsigned long)dst.ptr,
+ &dst.val, dst.bytes,
+ ctxt);
+ if (rc != 0)
+ goto done;
+ default:
+ break;
}
/* Commit shadow register state. */
Luca
--
Software is like sex; it's better when it's free.
Linus Torvalds
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