linux-kernel - Re: [PATCH 09/12] KVM: MMU: look for a cached PGD when going from 32-bit to 64-bit

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Message-ID: <YgW99wRxczsAJ0jv@google.com>
Date:   Fri, 11 Feb 2022 01:37:59 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        vkuznets@...hat.com, mlevitsk@...hat.com, dmatlack@...gle.com
Subject: Re: [PATCH 09/12] KVM: MMU: look for a cached PGD when going from
 32-bit to 64-bit

On Fri, Feb 11, 2022, Sean Christopherson wrote:
> On Wed, Feb 09, 2022, Paolo Bonzini wrote:
> Hmm, so it doesn't matter (yet) because shadowing 4-level NPT with 5-level NPT
> is fubar anyways[1], but this will prevent caching roots when shadowing 4-level
> NPT with 5-level NPT (have I mentioned how much I love NPT?).  This can be:
> 
> 	if (VALID_PAGE(mmu->root.hpa) && mmu->root.hpa == __pa(mmu->pae_root))

Gah, that's wrong too, it will allow the pml4_root case.  *sigh*  I'm fine punting
this until the special roots are less special, pml5_root is completely broken
anyways.