KVM: x86 emulator: fix in/out emulation.

in/out emulation is broken now. The breakage is different depending
on where IO device resides. If it is in userspace emulator reports
emulation failure since it incorrectly interprets kvm_emulate_pio()
return value. If IO device is in the kernel emulation of 'in' will do
nothing since kvm_emulate_pio() stores result directly into vcpu
registers, so emulator will overwrite result of emulation during
commit of shadowed register.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 7 insertions, 13 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index abbc3f9d03b2..e9f79619e185 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1494,29 +1494,23 @@ static int shutdown_interception(struct vcpu_svm *svm)
 
 static int io_interception(struct vcpu_svm *svm)
 {
+	struct kvm_vcpu *vcpu = &svm->vcpu;
 	u32 io_info = svm->vmcb->control.exit_info_1; /* address size bug? */
 	int size, in, string;
 	unsigned port;
 
 	++svm->vcpu.stat.io_exits;
-
-	svm->next_rip = svm->vmcb->control.exit_info_2;
-
 	string = (io_info & SVM_IOIO_STR_MASK) != 0;
-
-	if (string) {
-		if (emulate_instruction(&svm->vcpu,
-					0, 0, 0) == EMULATE_DO_MMIO)
-			return 0;
-		return 1;
-	}
-
 	in = (io_info & SVM_IOIO_TYPE_MASK) != 0;
+	if (string || in)
+		return !(emulate_instruction(vcpu, 0, 0, 0) == EMULATE_DO_MMIO);
+
 	port = io_info >> 16;
 	size = (io_info & SVM_IOIO_SIZE_MASK) >> SVM_IOIO_SIZE_SHIFT;
-
+	svm->next_rip = svm->vmcb->control.exit_info_2;
 	skip_emulated_instruction(&svm->vcpu);
-	return kvm_emulate_pio(&svm->vcpu, in, size, port);
+
+	return kvm_fast_pio_out(vcpu, size, port);
 }
 
 static int nmi_interception(struct vcpu_svm *svm)