linux-kernel - Re: [PATCH v2] KVM: SEV-ES: Don't intercept MSR_IA32

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Date: Wed, 22 May 2024 10:09:46 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Ravi Bangoria <ravi.bangoria@....com>
Cc: Sean Christopherson <seanjc@...gle.com>, thomas.lendacky@....com, tglx@...utronix.de, 
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, 
	hpa@...or.com, michael.roth@....com, nikunj.dadhania@....com, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, santosh.shukla@....com
Subject: Re: [PATCH v2] KVM: SEV-ES: Don't intercept MSR_IA32_DEBUGCTLMSR for
 SEV-ES guests

On Wed, May 22, 2024 at 8:11 AM Ravi Bangoria <ravi.bangoria@....com> wrote:
> >>> LBR Virtualization overhead for guest entry + exit roundtrip is ~450 cycles* on
> >>
> >> Ouch.  Just to clearify, that's for LBR Stack Virtualization, correct?
> >
> > And they are all in the VMSA, triggered by LBR_CTL_ENABLE_MASK, for
> > non SEV-ES guests?
>
> Not sure I follow. LBR_CTL_ENABLE_MASK works same for all types of guests.
> Just that, it's mandatory for SEV-ES guests and optional for SVM and SEV
> guests.

I think you confirmed I mean: when you set LBR_CTL_ENABLE_MASK, you
get the 450 cycle penalty because the whole set of LBR Stack MSRs is
in the VMSA for both SVM/SEV guests (optional) and SEV-ES guests
(mandatory).

Paolo