linux-kernel - Re: [PATCH 01/12] KVM: x86: host-initiated EFER.LME write affects the MMU

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Date:   Thu, 10 Feb 2022 22:49:57 +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,
        stable@...r.kernel.org
Subject: Re: [PATCH 01/12] KVM: x86: host-initiated EFER.LME write affects
 the MMU

On Wed, Feb 09, 2022, Paolo Bonzini wrote:
> While the guest runs, EFER.LME cannot change unless CR0.PG is clear, and therefore
> EFER.NX is the only bit that can affect the MMU role.  However, set_efer accepts
> a host-initiated change to EFER.LME even with CR0.PG=1.  In that case, the
> MMU has to be reset.
> 
> Fixes: 11988499e62b ("KVM: x86: Skip EFER vs. guest CPUID checks for host-initiated writes")
> Cc: stable@...r.kernel.org
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---

Ugh, but KVM_SET_SREGS handles this... It's basically KVM's equivalent of VMX putting
EFER in the VMCS, but then also allowing EFER in the load/store lists.

Reviewed-by: Sean Christopherson <seanjc@...gle.com>