linux-kernel - Re: [PATCH v2 1/2] KVM: SVM: Move asid to vcpu

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Message-ID: <f27e877e-b82b-ec9e-270e-cf8f23130b0b@redhat.com>
Date:   Mon, 30 Nov 2020 15:41:41 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ashish Kalra <Ashish.Kalra@....com>
Cc:     cavery@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, mlevitsk@...hat.com,
        vkuznets@...hat.com, wei.huang2@....com, thomas.lendacky@....com,
        brijesh.singh@....com, jon.grimm@....com
Subject: Re: [PATCH v2 1/2] KVM: SVM: Move asid to vcpu_svm

On 29/11/20 10:41, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....com>
> 
> This patch breaks SEV guests.
> 
> The patch stores current ASID in struct vcpu_svm and only moves it to VMCB in
> svm_vcpu_run(), but by doing so, the ASID allocated for SEV guests and setup
> in vmcb->control.asid by pre_sev_run() gets over-written by this ASID
> stored in struct vcpu_svm and hence, VMRUN fails as SEV guest is bound/activated
> on a different ASID then the one overwritten in vmcb->control.asid at VMRUN.
> 
> For example, asid#1 was activated for SEV guest and then vmcb->control.asid is
> overwritten with asid#0 (svm->asid) as part of this patch in svm_vcpu_run() and
> hence VMRUN fails.
> 

Thanks Ashish, I've sent a patch to fix it.

Would it be possible to add a minimal SEV test to 
tools/testing/selftests/kvm?  It doesn't have to do full attestation 
etc., if you can just write an "out" instruction using SEV_DBG_ENCRYPT 
and check that you can run it that's enough.

Paolo