linux-kernel - Re: [PATCH v3 7/9] KVM: nSVM: implement nested_svm_load

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Message-ID: <353dc97c-9754-68f9-6fb7-13671995e0a2@redhat.com>
Date:   Fri, 10 Jul 2020 14:08:30 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 7/9] KVM: nSVM: implement nested_svm_load_cr3() and use
 it for host->guest switch

On 10/07/20 13:40, Vitaly Kuznetsov wrote:
> Hm, it seems I missed svm_set_nested_state() path
> completely. Surprisingly, state_test didn't fail)
> 
> I'm struggling a bit to understand why we don't have kvm_set_cr3() on
> svm_set_nested_state() path: enter_svm_guest_mode() does it through
> nested_prepare_vmcb_save() but it is skipped in svm_set_nested_state().
> Don't we need it at least for !npt_enabled case?

In svm_set_nested_state you'll have CR3 already set to the right value.
 On the source, KVM_GET_SREGS returns the vmcb12's CR3 and it is already
restored with KVM_SET_SREGS on the destination before set_nested_state.

So, only the nested_cr3 has to be set.

Paolo

> We'll have to extract
> nested_cr3 from nested_vmcb then.