linux-kernel - Re: [PATCH 1/4] KVM: VMX: Refuse to load kvm

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Date:   Tue, 15 Jun 2021 15:26:31 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] KVM: VMX: Refuse to load kvm_intel if EPT and NX are disabled

On Tue, Jun 15, 2021 at 9:45 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Refuse to load KVM if NX support is not available and EPT is not enabled.
> Shadow paging has assumed NX support since commit 9167ab799362 ("KVM:
> vmx, svm: always run with EFER.NXE=1 when shadow paging is active"), so
> for all intents and purposes this has been a de facto requirement for
> over a year.
>
> Do not require NX support if EPT is enabled purely because Intel CPUs let
> firmware disable NX support via MSR_IA32_MISC_ENABLES.  If not for that,
> VMX (and KVM as a whole) could require NX support with minimal risk to
> breaking userspace.
>
> Fixes: 9167ab799362 ("KVM: vmx, svm: always run with EFER.NXE=1 when shadow paging is active")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Reviewed-by: Jim Mattson <jmattson@...gle.com>