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

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Date:   Fri, 10 Jul 2020 13:40:37 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...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

Paolo Bonzini <pbonzini@...hat.com> writes:

> On 09/07/20 19:57, Paolo Bonzini wrote:
>> On 09/07/20 16:53, Vitaly Kuznetsov wrote:
>>> +	if (nested_npt_enabled(svm))
>>> +		nested_svm_init_mmu_context(&svm->vcpu);
>>> +
>>>  	ret = nested_svm_load_cr3(&svm->vcpu, nested_vmcb->save.cr3,
>>>  				  nested_npt_enabled(svm));
>> 
>> This needs to be done in svm_set_nested_state, so my suggestion is that
>> the previous patch includes a call to nested_svm_load_cr3 in
>> svm_set_nested_state, and this one adds the "if" inside
>> nested_svm_load_cr3 itself.
>
> Actually no, that doesn't work after the next patch.  So the best option
> is probably to extract nested_svm_init_mmu as a separate step in
> enter_svm_guest_mode.  This also leaves nested_prepare_vmcb_save as a
> void function.
>

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

-- 
Vitaly