linux-kernel - Re: [PATCH 3/4] KVM: x86: WARN and reject loading KVM if NX is supported but not enabled

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Date:   Fri, 25 Jun 2021 11:04:59 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        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 3/4] KVM: x86: WARN and reject loading KVM if NX is
 supported but not enabled

On 25/06/21 00:33, Sean Christopherson wrote:
> On Tue, Jun 15, 2021, Sean Christopherson wrote:
>> WARN if NX is reported as supported but not enabled in EFER.  All flavors
>> of the kernel, including non-PAE 32-bit kernels, set EFER.NX=1 if NX is
>> supported, even if NX usage is disable via kernel command line.
> 
> Ugh, I misread .Ldefault_entry in head_32.S, it skips over the entire EFER code
> if PAE=0.  Apparently I didn't test this with non-PAE paging and EPT?
> 
> Paolo, I'll send a revert since it's in kvm/next, but even better would be if
> you can drop the patch :-)  Lucky for me you didn't pick up patch 4/4 that
> depends on this...
> 
> I'll revisit this mess in a few weeks.

Rather, let's keep this, see if anyone complains and possibly add a 
"depends on X86_PAE || X86_64" to KVM.

Paolo