Re: [PATCH] KVM: x86: clflushopt should be treated as a no-op by emulation

[Joao Martins]

On 11/3/20 12:04 PM, David Edmondson wrote:
> The instruction emulator ignores clflush instructions, yet fails to
> support clflushopt. Treat both similarly.
> 
> Fixes: 13e457e0eebf ("KVM: x86: Emulator does not decode clflush well")
> Signed-off-by: David Edmondson <david.edmondson@xxxxxxxxxx>

FWIW,

Reviewed-by: Joao Martins <joao.m.martins@xxxxxxxxxx>

> ---
>  arch/x86/kvm/emulate.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 0d917eb70319..56cae1ff9e3f 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -4046,6 +4046,12 @@ static int em_clflush(struct x86_emulate_ctxt *ctxt)
>  	return X86EMUL_CONTINUE;
>  }
>  
> +static int em_clflushopt(struct x86_emulate_ctxt *ctxt)
> +{
> +	/* emulating clflushopt regardless of cpuid */
> +	return X86EMUL_CONTINUE;
> +}
> +
>  static int em_movsxd(struct x86_emulate_ctxt *ctxt)
>  {
>  	ctxt->dst.val = (s32) ctxt->src.val;
> @@ -4585,7 +4591,7 @@ static const struct opcode group11[] = {
>  };
>  
>  static const struct gprefix pfx_0f_ae_7 = {
> -	I(SrcMem | ByteOp, em_clflush), N, N, N,
> +	I(SrcMem | ByteOp, em_clflush), I(SrcMem | ByteOp, em_clflushopt), N, N,
>  };
>  
>  static const struct group_dual group15 = { {
>