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

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Message-ID: <09a49caf-6ff5-295b-d1ab-023549f6a23b@redhat.com>
Date:   Fri, 25 Jun 2021 10:57:51 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     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 25/06/21 10:47, Yu Zhang wrote:
>> But if L1 is crafty, it can load a new CR4 on VM-Exit and toggle LA57
>> without having to bounce through an unpaged section.  L1 can also load a
>
> May I ask how this is done by the guest? Thanks!

It can set HOST_CR3 and HOST_CR4 to a value that is different from the 
one on vmentry.

Paolo