linux-kernel - Re: [PATCH 25/30] KVM: nSVM: leave guest mode when clearing EFER.SVME

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Message-ID: <9319ccf9-c318-40e8-7d56-df0e32617430@redhat.com>
Date:   Mon, 1 Jun 2020 09:28:10 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Krish Sadhukhan <krish.sadhukhan@...cle.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 25/30] KVM: nSVM: leave guest mode when clearing EFER.SVME

On 01/06/20 04:26, Krish Sadhukhan wrote:
> On 5/29/20 8:39 AM, Paolo Bonzini wrote:
>> According to the AMD manual, the effect of turning off EFER.SVME while a
>> guest is running is undefined.  We make it leave guest mode immediately,
>> similar to the effect of clearing the VMX bit in MSR_IA32_FEAT_CTL.
> 
> I see that svm_set_efer() is called in enter_svm_guest_mode() and
> nested_svm_vmexit(). In the VMRUN path, we have already checked
> EFER.SVME in nested_vmcb_checks(). So if it was not set, we wouldn't
> come to enter_svm_guest_mode(). Your fix is only for the #VMEXIT path
> then ?

No, it's for KVM_SET_MSR.

Paolo