linux-kernel - Re: [PATCH 00/10] KVM: SVM: Attempt to cleanup SEV

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Message-ID: <a9d70abe-d229-81cb-4d9a-6106cef612a4@amd.com>
Date: Thu, 20 Feb 2025 16:51:01 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Naveen N Rao <naveen@...nel.org>, Kim Phillips <kim.phillips@....com>,
 Alexey Kardashevskiy <aik@....com>
Subject: Re: [PATCH 00/10] KVM: SVM: Attempt to cleanup SEV_FEATURES

On 2/18/25 19:26, Sean Christopherson wrote:
> This is a hastily thrown together series, barely above RFC, to try and
> address the worst of the issues that arise with guest controlled SEV
> features (thanks AP creation)[1].
> 
> In addition to the initial flaws with DebugSwap, I came across a variety
> of issues when trying to figure out how best to handle SEV features in
> general.  E.g. AFAICT, KVM doesn't guard against userspace manually making
> a vCPU RUNNABLE after it has been DESTROYED (or after a failed CREATE).
> 
> This is essentially compile-tested only, as I don't have easy access to a
> system with SNP enabled.  I ran the SEV-ES selftests, but that's not much
> in the way of test coverage.
> 
> AMD folks, I would greatly appreciate reviews, testing, and most importantly,
> confirmation that all of this actually works the way I think it does.

A quick test of a 64 vCPU SNP guest booted successfully, so that's a
good start. I'll take a closer look at these patches over the next few days.

Thanks,
Tom

> 
> [1] https://lore.kernel.org/all/Z7TSef290IQxQhT2@google.com
> 
> Sean Christopherson (10):
>   KVM: SVM: Save host DR masks but NOT DRs on CPUs with DebugSwap
>   KVM: SVM: Don't rely on DebugSwap to restore host DR0..DR3
>   KVM: SVM: Terminate the VM if a SEV-ES+ guest is run with an invalid
>     VMSA
>   KVM: SVM: Don't change target vCPU state on AP Creation VMGEXIT error
>   KVM: SVM: Require AP's "requested" SEV_FEATURES to match KVM's view
>   KVM: SVM: Simplify request+kick logic in SNP AP Creation handling
>   KVM: SVM: Use guard(mutex) to simplify SNP AP Creation error handling
>   KVM: SVM: Mark VMCB dirty before processing incoming snp_vmsa_gpa
>   KVM: SVM: Use guard(mutex) to simplify SNP vCPU state updates
>   KVM: SVM: Invalidate "next" SNP VMSA GPA even on failure
> 
>  arch/x86/kvm/svm/sev.c | 218 +++++++++++++++++++----------------------
>  arch/x86/kvm/svm/svm.c |   7 +-
>  arch/x86/kvm/svm/svm.h |   2 +-
>  3 files changed, 106 insertions(+), 121 deletions(-)
> 
> 
> base-commit: fed48e2967f402f561d80075a20c5c9e16866e53