Re: [PATCH v3 7/9] KVM: nSVM: implement nested_svm_load_cr3() and use it for host->guest switch

Vitaly Kuznetsov
2020-07-10T12:30:44Z

Paolo Bonzini <pbonzini@redhat.com> writes:

> 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.
>

Ah, thanks, so it seems there is no need to merge nested_svm_load_cr3()
(former kvm_set_cr3()) with nested_svm_init_mmu_context() in a new
nested_svm_init_mmu() as we'll only need the latter on
svm_set_nested_state(). We can just move nested_svm_load_cr3() out of
nested_prepare_vmcb_save() to enter_svm_guest_mode().

--
Vitaly