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:   Wed, 7 Jul 2021 16:15:49 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     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 list <kvm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        lkft-triage@...ts.linaro.org, regressions@...ts.linux.dev
Subject: Re: [PATCH 3/4] KVM: x86: WARN and reject loading KVM if NX is
 supported but not enabled

On 07/07/21 14:09, Naresh Kamboju wrote:
> On Fri, 25 Jun 2021 at 14:35, Paolo Bonzini <pbonzini@...hat.com> wrote:
>>
>> 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.
> 
> [ please ignore if this is already reported ]
> 
> The following kernel warning noticed while booting linus master branch and
> Linux next 20210707 tag on i386 kernel booting on x86_64 machine.

Ok, so the "depends on" is needed.  Let's add it, I'm getting back to 
KVM work and will send the patch today or tomorrow.

Paolo