linux-kernel - Re: [PATCH v2 01/11] KVM: nSVM: don't sync back tlb

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Message-ID: <439f0b8b52dd019c60974ab105dee75fa15eaf3e.camel@redhat.com>
Date:   Tue, 06 Dec 2022 14:13:26 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Santosh Shukla <santosh.shukla@....com>, kvm@...r.kernel.org
Cc:     Sandipan Das <sandipan.das@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        Jiaxi Chen <jiaxi.chen@...ux.intel.com>,
        Babu Moger <babu.moger@....com>, linux-kernel@...r.kernel.org,
        Jing Liu <jing2.liu@...el.com>,
        Wyes Karny <wyes.karny@....com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH v2 01/11] KVM: nSVM: don't sync back tlb_ctl on nested
 VM exit

On Mon, 2022-12-05 at 19:35 +0530, Santosh Shukla wrote:
> 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)

True for both changes, thanks!

Best regards,
	Maxim Levitsky

> 
> >   "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@...hat.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;
> >