linux-kernel - Re: [PATCH 0/4] KVM: x86: Require EFER.NX support unless EPT is on

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Date:   Fri, 18 Jun 2021 12:32:04 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     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
Subject: Re: [PATCH 0/4] KVM: x86: Require EFER.NX support unless EPT is on

On 15/06/21 18:45, Sean Christopherson wrote:
> KVM has silently required EFER.NX support for shadow paging for well over
> a year, and for NPT for roughly the same amount of time.  Attempting to
> run any VM with shadow paging on a system without NX support will fail due
> to invalid state, while enabling nx_huge_pages with NPT and no NX will
> explode due to setting a reserved bit in the page tables.
> 
> I really, really wanted to require NX across the board, because the lack
> of bug reports for the shadow paging change strongly suggests no one is
> running KVM on a CPU that truly doesn't have NX.  But, Intel CPUs let
> firmware disable NX via MISC_ENABLES, so it's plausible that there are
> users running KVM with EPT and no NX.
> 
> Sean Christopherson (4):
>    KVM: VMX: Refuse to load kvm_intel if EPT and NX are disabled
>    KVM: SVM: Refuse to load kvm_amd if NX support is not available
>    KVM: x86: WARN and reject loading KVM if NX is supported but not
>      enabled
>    KVM: x86: Simplify logic to handle lack of host NX support
> 
>   arch/x86/kvm/cpuid.c   | 13 +++++--------
>   arch/x86/kvm/svm/svm.c | 13 ++++++++++---
>   arch/x86/kvm/vmx/vmx.c |  6 ++++++
>   arch/x86/kvm/x86.c     |  3 +++
>   4 files changed, 24 insertions(+), 11 deletions(-)
> 

Queued 1-3, thanks.

Paolo