Re: [PATCH] KVM: x86 emulator: emulate MOVNTDQ

From: Eric Northup
Date: Fri Jul 11 2014 - 15:32:00 EST


On Fri, Jul 11, 2014 at 10:56 AM, Alex Williamson
<alex.williamson@xxxxxxxxxx> wrote:
> Windows 8.1 guest with NVIDIA driver and GPU fails to boot with an
> emulation failure. The KVM spew suggests the fault is with lack of
> movntdq emulation (courtesy of Paolo):
>
> Code=02 00 00 b8 08 00 00 00 f3 0f 6f 44 0a f0 f3 0f 6f 4c 0a e0 <66> 0f e7 41 f0 66 0f e7 49 e0 48 83 e9 40 f3 0f 6f 44 0a 10 f3 0f 6f 0c 0a 66 0f e7 41 10
>
> $ as -o a.out
> .section .text
> .byte 0x66, 0x0f, 0xe7, 0x41, 0xf0
> .byte 0x66, 0x0f, 0xe7, 0x49, 0xe0
> $ objdump -d a.out
> 0: 66 0f e7 41 f0 movntdq %xmm0,-0x10(%rcx)
> 5: 66 0f e7 49 e0 movntdq %xmm1,-0x20(%rcx)
>
> Add the necessary emulation.
>
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>
> Hope I got all the flags correct from copying similar MOV ops, but it
> allows the guest to boot, so I suspect it's ok.
>
> arch/x86/kvm/emulate.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index e4e833d..ae39f08 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -3681,6 +3681,10 @@ static const struct gprefix pfx_0f_28_0f_29 = {
> I(Aligned, em_mov), I(Aligned, em_mov), N, N,
> };
>
> +static const struct gprefix pfx_0f_e7 = {
> + N, I(Sse, em_mov), N, N,

I think you need 'Aligned' flag in here - from my reading of the
manual, this instruction will #GP if the memory operand isn't aligned.

> +};
> +
> static const struct escape escape_d9 = { {
> N, N, N, N, N, N, N, I(DstMem, em_fnstcw),
> }, {
> @@ -3951,7 +3955,8 @@ static const struct opcode twobyte_table[256] = {
> /* 0xD0 - 0xDF */
> N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N,
> /* 0xE0 - 0xEF */
> - N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N,
> + N, N, N, N, N, N, N, GP(SrcReg | DstMem | ModRM | Mov, &pfx_0f_e7),
> + N, N, N, N, N, N, N, N,
> /* 0xF0 - 0xFF */
> N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N
> };
>
> --
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