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From: Yu Zhang <yu.c.zhang@linux.intel.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Maxim Levitsky <mlevitsk@redhat.com>
Subject: Re: [PATCH 08/12] KVM: nSVM: Use KVM-governed feature framework to track "vVM{SAVE,LOAD} enabled"
Date: Fri, 30 Jun 2023 18:00:01 +0800	[thread overview]
Message-ID: <20230630100001.vmzlrtaw5fq5pisn@linux.intel.com> (raw)
In-Reply-To: <ZJ22Wts4WKKD19bN@google.com>

On Thu, Jun 29, 2023 at 09:50:34AM -0700, Sean Christopherson wrote:
> On Wed, Feb 22, 2023, Sean Christopherson wrote:
> > +Maxim
> > 
> > On Wed, Feb 22, 2023, Yu Zhang wrote:
> > I'll opportunistically massage the comment to make it more explicit about why
> > VMLOAD needs to be intercepted.
> >  
> > That said, clearing the bits for this seems wrong.  That would corrupt the MSRs
> > for 64-bit Intel guests.  The "target" of the fix was 32-bit L2s, i.e. I doubt
> > anything would notice.
> > 
> >     This patch fixes nested migration of 32 bit nested guests, that was
> >     broken because incorrect cached values of SYSENTER msrs were stored in
> >     the migration stream if L1 changed these msrs with
> >     vmload prior to L2 entry.
> 
> Aha!  Finally figured out what this code is doing.  KVM intercepts VMLOAD so that
> KVM can correctly model the VMLOAD behavior of dropping bits 63:32, i.e. to clear
> svm->sysenter_eip_hi and svm->sysenter_esp_hi.
> 
> So the code is correct.  I'll add this comment:
> 
> 	/*
> 	 * Intercept VMLOAD if the vCPU mode is Intel in order to emulate that
> 	 * VMLOAD drops bits 63:32 of SYSENTER (ignoring the fact that exposing
> 	 * SVM on Intel is bonkers and extremely unlikely to work).
> 	 */
> 
Oh.. Because L2 will never be a 64-bit Intel guest, and the emulation of vmload
shall follow APM's requirement(to clear the upper 32 bits)?

Thanks a lot for bring me back to this discussion... I totally forgot it. :)

B.R.
Yu
 
Thanks a lot for this explanation, Sean! 

  reply	other threads:[~2023-06-30 10:00 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-17 23:10 [PATCH 00/12] KVM: x86: Add "governed" X86_FEATURE framework Sean Christopherson
2023-02-17 23:10 ` [PATCH 01/12] KVM: x86: Add a framework for enabling KVM-governed x86 features Sean Christopherson
2023-02-21 17:12   ` Vitaly Kuznetsov
2023-06-29  2:40   ` Binbin Wu
2023-06-29 16:26     ` Sean Christopherson
2023-06-30  8:01   ` Chao Gao
2023-06-30 15:31     ` Sean Christopherson
2023-02-17 23:10 ` [PATCH 02/12] KVM: x86/mmu: Use KVM-governed feature framework to track "GBPAGES enabled" Sean Christopherson
2023-02-17 23:10 ` [PATCH 03/12] KVM: VMX: Recompute "XSAVES enabled" only after CPUID update Sean Christopherson
2023-02-17 23:10 ` [PATCH 04/12] KVM: VMX: Rename XSAVES control to follow KVM's preferred "ENABLE_XYZ" Sean Christopherson
2023-02-17 23:10 ` [PATCH 05/12] KVM: x86: Use KVM-governed feature framework to track "XSAVES enabled" Sean Christopherson
2023-02-21 14:56   ` Yu Zhang
2023-02-22 18:56     ` Sean Christopherson
2023-02-24  9:54       ` Yu Zhang
2023-02-17 23:10 ` [PATCH 06/12] KVM: nSVM: Use KVM-governed feature framework to track "NRIPS enabled" Sean Christopherson
2023-02-17 23:10 ` [PATCH 07/12] KVM: nSVM: Use KVM-governed feature framework to track "TSC scaling enabled" Sean Christopherson
2023-02-17 23:10 ` [PATCH 08/12] KVM: nSVM: Use KVM-governed feature framework to track "vVM{SAVE,LOAD} enabled" Sean Christopherson
2023-02-21 15:23   ` Yu Zhang
2023-02-21 15:33     ` Yu Zhang
2023-02-21 23:48       ` Sean Christopherson
2023-02-22  6:49         ` Yu Zhang
2023-02-22 16:39           ` Sean Christopherson
2023-02-24  9:25             ` Yu Zhang
2023-02-24 16:16               ` Sean Christopherson
2023-06-29 16:50             ` Sean Christopherson
2023-06-30 10:00               ` Yu Zhang [this message]
2023-02-17 23:10 ` [PATCH 09/12] KVM: nSVM: Use KVM-governed feature framework to track "LBRv enabled" Sean Christopherson
2023-02-17 23:10 ` [PATCH 10/12] KVM: nSVM: Use KVM-governed feature framework to track "Pause Filter enabled" Sean Christopherson
2023-02-17 23:10 ` [PATCH 11/12] KVM: nSVM: Use KVM-governed feature framework to track "vGIF enabled" Sean Christopherson
2023-02-17 23:10 ` [PATCH 12/12] KVM: x86: Disallow guest CPUID lookups when IRQs are disabled Sean Christopherson

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