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From: Richard Henderson <rth@twiddle.net>
Message-ID: <563C8958.20709@twiddle.net>
Date: Fri, 6 Nov 2015 12:04:56 +0100
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Subject: Re: [Qemu-devel] [PATCH 1/2] target-i386: tcg: Accept clwb
	instruction
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To: Eduardo Habkost <ehabkost@redhat.com>, qemu-devel@nongnu.org
Cc: Paolo Bonzini <pbonzini@redhat.com>, Xiao Guangrong <guangrong.xiao@linux.intel.com>, kvm@vger.kernel.org

On 11/04/2015 10:24 PM, Eduardo Habkost wrote:
> Accept the clwb instruction (66 0F AE /6) if its corresponding feature
> flag is enabled on CPUID[7].
>
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> ---
>   target-i386/translate.c | 13 ++++++++++++-
>   1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/target-i386/translate.c b/target-i386/translate.c
> index b400d24..bac1685 100644
> --- a/target-i386/translate.c
> +++ b/target-i386/translate.c
> @@ -7716,10 +7716,21 @@ static target_ulong disas_insn(CPUX86State *env, DisasContext *s,
>               }
>               break;
>           case 5: /* lfence */
> -        case 6: /* mfence */
>               if ((modrm & 0xc7) != 0xc0 || !(s->cpuid_features & CPUID_SSE2))
>                   goto illegal_op;
>               break;
> +        case 6: /* mfence/clwb */
> +            if (s->prefix & PREFIX_DATA) {
> +                /* clwb */
> +                if (!(s->cpuid_7_0_ebx_features & CPUID_7_0_EBX_CLWB))
> +                    goto illegal_op;
> +                gen_lea_modrm(env, s, modrm);

You should use gen_nop_modrm here, since we're not going to do anything with 
the address.  Otherwise,

Reviewed-by: Richard Henderson <rth@twiddle.net>


r~