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Date:   Wed, 18 Aug 2021 21:43:09 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Hou Wenlong <houwenlong93@linux.alibaba.com>
Cc:     kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Avi Kivity <avi@redhat.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kvm: fix wrong exception emulation in check_rdtsc
Message-ID: <YR1+7awNToPmkitb@google.com>
References: <1297c0dd3f1bb47a6d089f850b629c7aa0247040.1629257115.git.houwenlong93@linux.alibaba.com>
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On Wed, Aug 18, 2021, Hou Wenlong wrote:
> According to Intel's SDM Vol2 and AMD's APM Vol3, when
> CR4.TSD is set, use rdtsc/rdtscp instruction above privilege
> level 0 should trigger a #GP.
> 
> Fixes: d7eb82030699e ("KVM: SVM: Add intercept checks for remaining group7 instructions")
> Signed-off-by: Hou Wenlong <houwenlong93@linux.alibaba.com>
> ---
>  arch/x86/kvm/emulate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 2837110e66ed..c589ac832265 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -4206,7 +4206,7 @@ static int check_rdtsc(struct x86_emulate_ctxt *ctxt)
>  	u64 cr4 = ctxt->ops->get_cr(ctxt, 4);
>  
>  	if (cr4 & X86_CR4_TSD && ctxt->ops->cpl(ctxt))
> -		return emulate_ud(ctxt);
> +		return emulate_gp(ctxt, 0);

Heh, I was having some serious deja vu, but the fix I was thinking of was
for em_rdpid, and that was changing #GP -> #UD (commit a9e2e0ae6860).

Reviewed-by: Sean Christopherson <seanjc@google.com>

>  	return X86EMUL_CONTINUE;
>  }
> -- 
> 2.31.1
>