linux-kernel - Re: [PATCH 21/24] KVM: x86: always update CR3 in VMCB

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Date:   Wed, 20 May 2020 11:24:39 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        vkuznets@...hat.com, Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 21/24] KVM: x86: always update CR3 in VMCB

Oh, and it'd be nice to do s/VMCB/VMCB\/VMCS in the subject, I almost
glossed over this patch because it explicitly said VMCB :-)

On Wed, May 20, 2020 at 01:21:42PM -0400, Paolo Bonzini wrote:
> vmx_load_mmu_pgd is delaying the write of GUEST_CR3 to prepare_vmcs02 as
> an optimization, but this is only correct before the nested vmentry.
> If userspace is modifying CR3 with KVM_SET_SREGS after the VM has
> already been put in guest mode, the value of CR3 will not be updated.
> Remove the optimization, which almost never triggers anyway.
> 
> This also applies to SVM, where the code was added in commit 689f3bf21628
> ("KVM: x86: unify callbacks to load paging root", 2020-03-16) just to keep the
> two vendor-specific modules closer.
> 
> Fixes: 04f11ef45810 ("KVM: nVMX: Always write vmcs02.GUEST_CR3 during nested VM-Enter")
> Fixes: 689f3bf21628 ("KVM: x86: unify callbacks to load paging root")
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---