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, 8 insertions, 10 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 87b3c6843aac..1cceca1c59be 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2985,22 +2985,20 @@ static int handle_io(struct kvm_vcpu *vcpu)
         int size, in, string;
         unsigned port;
 
-        ++vcpu->stat.io_exits;
         exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
         string = (exit_qualification & 16) != 0;
+        in = (exit_qualification & 8) != 0;
 
-        if (string) {
-                if (emulate_instruction(vcpu, 0, 0, 0) == EMULATE_DO_MMIO)
-                        return 0;
-                return 1;
-        }
+        ++vcpu->stat.io_exits;
 
-        size = (exit_qualification & 7) + 1;
-        in = (exit_qualification & 8) != 0;
-        port = exit_qualification >> 16;
+        if (string || in)
+                return !(emulate_instruction(vcpu, 0, 0, 0) == EMULATE_DO_MMIO);
 
+        port = exit_qualification >> 16;
+        size = (exit_qualification & 7) + 1;
         skip_emulated_instruction(vcpu);
-        return kvm_emulate_pio(vcpu, in, size, port);
+
+        return kvm_fast_pio_out(vcpu, size, port);
 }
 
 static void