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authorLuca Tettamanti <kronos.it@gmail.com>2007-06-19 22:41:20 +0200
committerAvi Kivity <avi@qumranet.com>2007-07-16 12:05:48 +0300
commit02c03a326a5df825cc01de426f72e160db2b9538 (patch)
tree6b6e765fbe03832a7fd68c4c28e7f105875d40ed
parent74906345ff9f84f2b3b772d368c7e49f4ba27456 (diff)
KVM: Fix x86 emulator writeback
When the old value and new one are the same the emulator skips the write; this is undesirable 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 perform the writeback stage in the emulation unless it's explicitly disabled (currently push and some 2 bytes instructions may disable the writeback). Signed-Off-By: Luca Tettamanti <kronos.it@gmail.com> Signed-off-by: Avi Kivity <avi@qumranet.com>
-rw-r--r--drivers/kvm/x86_emulate.c9
1 files changed, 5 insertions, 4 deletions
diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index 92620e48f06..f60012d6261 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -485,6 +485,7 @@ x86_emulate_memop(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
int mode = ctxt->mode;
unsigned long modrm_ea;
int use_modrm_ea, index_reg = 0, base_reg = 0, scale, rip_relative = 0;
+ int no_wb = 0;
/* Shadow copy of register state. Committed on successful emulation. */
unsigned long _regs[NR_VCPU_REGS];
@@ -1051,7 +1052,7 @@ done_prefixes:
_regs[VCPU_REGS_RSP]),
&dst.val, dst.bytes, ctxt)) != 0)
goto done;
- dst.val = dst.orig_val; /* skanky: disable writeback */
+ no_wb = 1;
break;
default:
goto cannot_emulate;
@@ -1060,7 +1061,7 @@ done_prefixes:
}
writeback:
- if ((d & Mov) || (dst.orig_val != dst.val)) {
+ if (!no_wb) {
switch (dst.type) {
case OP_REG:
/* The 4-byte case *is* correct: in 64-bit mode we zero-extend. */
@@ -1168,7 +1169,7 @@ pop_instruction:
goto done;
register_address_increment(_regs[VCPU_REGS_RSP], op_bytes);
- dst.orig_val = dst.val; /* Disable writeback. */
+ no_wb = 1; /* Disable writeback. */
break;
}
goto writeback;
@@ -1323,7 +1324,7 @@ twobyte_insn:
twobyte_special_insn:
/* Disable writeback. */
- dst.orig_val = dst.val;
+ no_wb = 1;
switch (b) {
case 0x09: /* wbinvd */
break;