KVM: x86: #PF error-code on R/W operations is wrong
When emulating an instruction that reads the destination memory operand (i.e.,
instructions without the Mov flag in the emulator), the operand is first read.
If a page-fault is detected in this phase, the error-code which would be
delivered to the VM does not indicate that the access that caused the exception
is a write one. This does not conform with real hardware, and may cause the VM
to enter the page-fault handler twice for no reason (once for read, once for
write).
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 d949287..ef23c1e 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4909,8 +4909,12 @@
/* optimisation - avoid slow emulated read if Mov */
rc = segmented_read(ctxt, ctxt->dst.addr.mem,
&ctxt->dst.val, ctxt->dst.bytes);
- if (rc != X86EMUL_CONTINUE)
+ if (rc != X86EMUL_CONTINUE) {
+ if (rc == X86EMUL_PROPAGATE_FAULT &&
+ ctxt->exception.vector == PF_VECTOR)
+ ctxt->exception.error_code |= PFERR_WRITE_MASK;
goto done;
+ }
}
ctxt->dst.orig_val = ctxt->dst.val;