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Date:   Mon, 5 Dec 2022 19:35:04 +0530
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Subject: Re: [PATCH v2 01/11] KVM: nSVM: don't sync back tlb_ctl on nested VM
 exit
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To:     Maxim Levitsky <mlevitsk@redhat.com>, kvm@vger.kernel.org
Cc:     Sandipan Das <sandipan.das@amd.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Daniel Sneddon <daniel.sneddon@linux.intel.com>,
        Jiaxi Chen <jiaxi.chen@linux.intel.com>,
        Babu Moger <babu.moger@amd.com>, linux-kernel@vger.kernel.org,
        Jing Liu <jing2.liu@intel.com>,
        Wyes Karny <wyes.karny@amd.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Sean Christopherson <seanjc@google.com>, santosh.shukla@amd.com
References: <20221129193717.513824-1-mlevitsk@redhat.com>
 <20221129193717.513824-2-mlevitsk@redhat.com>
From:   Santosh Shukla <santosh.shukla@amd.com>
In-Reply-To: <20221129193717.513824-2-mlevitsk@redhat.com>
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Hi Maxim,

On 11/30/2022 1:07 AM, Maxim Levitsky wrote:
> The CPU doesn't change TLB_CTL value as stated in the PRM (15.16.2):
> 
nits:
s / PRM (15.16.2) / APM (15.16.1 - TLB Flush)

>   "The VMRUN instruction reads, but does not change, the
>   value of the TLB_CONTROL field"
> 
> Therefore the KVM shouldn't do that either.
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>  arch/x86/kvm/svm/nested.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index bc9cd7086fa972..37af0338da7c32 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -1010,7 +1010,6 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
>  		vmcb12->control.next_rip  = vmcb02->control.next_rip;
>  
>  	vmcb12->control.int_ctl           = svm->nested.ctl.int_ctl;
> -	vmcb12->control.tlb_ctl           = svm->nested.ctl.tlb_ctl;
>  	vmcb12->control.event_inj         = svm->nested.ctl.event_inj;
>  	vmcb12->control.event_inj_err     = svm->nested.ctl.event_inj_err;
>