linux-kernel - Re: [PATCH] KVM: SVM: Use a separate vmcb for the nested L2 guest

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Message-ID: <a6ed7866-69c3-ab5e-7219-d7c5075509db@redhat.com>
Date:   Tue, 22 Sep 2020 17:04:39 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Cathy Avery <cavery@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     vkuznets@...hat.com, wei.huang2@....com
Subject: Re: [PATCH] KVM: SVM: Use a separate vmcb for the nested L2 guest

On 17/09/20 21:23, Cathy Avery wrote:
> 
> 2) There is a workaround in nested_svm_vmexit() where
> 
>    if (svm->vmcb01->control.asid == 0)
>        svm->vmcb01->control.asid = svm->nested.vmcb02->control.asid;
> 
>    This was done as a result of the kvm selftest 'state_test'. In that
>    test svm_set_nested_state() is called before svm_vcpu_run().
>    The asid is assigned by svm_vcpu_run -> pre_svm_run for the current
>    vmcb which is now vmcb02 as we are in nested mode subsequently
>    vmcb01.control.asid is never set as it should be.

I think the asid should be kept in svm->asid, and copied to
svm->vmcb->control.asid in svm_vcpu_run.  It's slightly overkill for
non-nested but it simplifies the nested case a lot so it's worth it.

That would be a first patch in the series, placed before this one.

Paolo