Re: [PATCH v2 25/30] KVM: x86 emulator: fix in/out emulation.

[Gleb Natapov <gleb@redhat.com>]

On Mon, Mar 15, 2010 at 09:41:51AM +0200, Avi Kivity wrote:
> On 03/14/2010 07:35 PM, Gleb Natapov wrote:
> >On Sun, Mar 14, 2010 at 06:54:11PM +0200, Avi Kivity wrote:
> >>On 03/14/2010 06:21 PM, Gleb Natapov wrote:
> >>>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.
> >>>
> >>>
> >>>diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> >>>index 8f5e4c8..344e17b 100644
> >>>--- a/arch/x86/kvm/emulate.c
> >>>+++ b/arch/x86/kvm/emulate.c
> >>>@@ -210,13 +210,13 @@ static u32 opcode_table[256] = {
> >>>  	0, 0, 0, 0, 0, 0, 0, 0,
> >>>  	/* 0xE0 - 0xE7 */
> >>>  	0, 0, 0, 0,
> >>>-	ByteOp | SrcImmUByte, SrcImmUByte,
> >>>-	ByteOp | SrcImmUByte, SrcImmUByte,
> >>>+	ByteOp | SrcImmUByte | DstAcc, SrcImmUByte | DstAcc,
> >>>+	ByteOp | SrcImmUByte | DstAcc, SrcImmUByte | DstAcc,
> >>REX prefix shouldn't expand DstAcc to 64 bits here.  Might cause
> >>problems further down in the pipeline.+
> >Is REX prefix allowed with this opcodes?
> >
> >If yes:
> >
> >if (c->dst.bytes == 8)
> >	c->dst.bytes = 4;
> >
> >inside IN/OUT emulation will fix this.
> 
> I don't know, but I guess REX is allowed and ignored.
> 
Hmm, curious. I'll test.

--
			Gleb.