Re: [PATCH] KVM: x86/mmu: Calculate and check "full" mmu_role for nested MMU

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/06/21 18:45, Sean Christopherson wrote:
>> Along which path though?  I would have naively expected those to be driven
>> only by the context->root_level.
> The functional code is driven by context->root_level, but if KVM doesn't include
> the level in the mmu_role then it will fail to update context->root_level when
> L2 changes from 32-bit PAE to 64-bit.  If all the CR0/CR4/EFER bits remain the
> same, only the level will differ.  Without this patch, role.level is always '0'
> for the nested MMU.
> 

Yes the problem is the

         if (new_role.as_u64 == g_context->mmu_role.as_u64)
                 return;

and the patch lets you preserve the optimization instead of dropping it. 
  I was wondering if I was missing something else because of the "when 
walking the guest page tables" remark.

Paolo