KVM: x86: fnstcw and fnstsw may cause spurious exception
Since the operand size of fnstcw and fnstsw is updated during the execution,
the emulation may cause spurious exceptions as it reads the memory beforehand.
Marking these instructions as Mov (since the previous value is ignored) and
DstMem16 to simplify the setting of operand size.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index abe95d2..fff1188 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -86,6 +86,7 @@
#define DstAcc (OpAcc << DstShift)
#define DstDI (OpDI << DstShift)
#define DstMem64 (OpMem64 << DstShift)
+#define DstMem16 (OpMem16 << DstShift)
#define DstImmUByte (OpImmUByte << DstShift)
#define DstDX (OpDX << DstShift)
#define DstAccLo (OpAccLo << DstShift)
@@ -1057,8 +1058,6 @@
asm volatile("fnstcw %0": "+m"(fcw));
ctxt->ops->put_fpu(ctxt);
- /* force 2 byte destination */
- ctxt->dst.bytes = 2;
ctxt->dst.val = fcw;
return X86EMUL_CONTINUE;
@@ -1075,8 +1074,6 @@
asm volatile("fnstsw %0": "+m"(fsw));
ctxt->ops->put_fpu(ctxt);
- /* force 2 byte destination */
- ctxt->dst.bytes = 2;
ctxt->dst.val = fsw;
return X86EMUL_CONTINUE;
@@ -3863,7 +3860,7 @@
};
static const struct escape escape_d9 = { {
- N, N, N, N, N, N, N, I(DstMem, em_fnstcw),
+ N, N, N, N, N, N, N, I(DstMem16 | Mov, em_fnstcw),
}, {
/* 0xC0 - 0xC7 */
N, N, N, N, N, N, N, N,
@@ -3905,7 +3902,7 @@
} };
static const struct escape escape_dd = { {
- N, N, N, N, N, N, N, I(DstMem, em_fnstsw),
+ N, N, N, N, N, N, N, I(DstMem16 | Mov, em_fnstsw),
}, {
/* 0xC0 - 0xC7 */
N, N, N, N, N, N, N, N,