linux-kernel - Re: [PATCH 05/54] Revert "KVM: x86/mmu: Drop kvm_mmu_extended_role.cr4

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Message-ID: <20210625112314.nn6llnk7dtovjg4e@linux.intel.com>
Date:   Fri, 25 Jun 2021 19:23:14 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH 05/54] Revert "KVM: x86/mmu: Drop
 kvm_mmu_extended_role.cr4_la57 hack"

On Fri, Jun 25, 2021 at 12:25:46PM +0200, Paolo Bonzini wrote:
> On 25/06/21 11:29, Yu Zhang wrote:
> > Thanks, Paolo.
> > 
> > Do you mean the L1 can modify its paging mode by setting HOST_CR3 as root of
> > a PML5 table in VMCS12 and HOST_CR4 with LA57 flipped in VMCS12, causing the
> > GUEST_CR3/4 being changed in VMCS01, and eventually updating the CR3/4 when
> > L0 is injecting a VM Exit from L2?
> 
> Yes, you can even do that without a "full" vmentry by setting invalid guest
> state in vmcs12. :)

Hah.. Interesting. :) I think this is what load_vmcs12_host_state() does. Anyway,
thanks a lot for the explanation!

Also my reviewed-by for this one.

Rviewed-by: Yu Zhang <yu.c.zhang@...ux.intel.com>

B.R.
Yu