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

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Message-ID: <2f1e370f-2dbf-2935-ba26-b6dacf6eec0d@oracle.com>
Date:   Fri, 13 Nov 2020 11:07:31 +0000
From:   Joao Martins <joao.m.martins@...cle.com>
To:     David Edmondson <david.edmondson@...cle.com>, kvm@...r.kernel.org
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Nadav Amit <namit@...technion.ac.il>, x86@...nel.org,
        Wanpeng Li <wanpengli@...cent.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
        Jim Mattson <jmattson@...gle.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: clflushopt should be treated as a no-op by
 emulation

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@...cle.com>

FWIW,

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

> ---
>  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 = { {
>