linux-kernel - Re: [PATCH 4/4] KVM: x86: Simplify logic to handle lack of host NX support

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Message-ID: <24c8db9d-cee3-7f43-08fc-287bca4d6f08@redhat.com>
Date:   Fri, 18 Jun 2021 12:31:41 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>
Cc:     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 4/4] KVM: x86: Simplify logic to handle lack of host NX
 support

On 16/06/21 01:33, Sean Christopherson wrote:
>> It would be nice if we chose one consistent approach to dealing with
>> invalid guest CPUID information and stuck with it. Silently modifying
>> the table provided by userspace seems wrong to me. I much prefer the
>> kvm_check_cpuid approach of telling userspace that the guest CPUID
>> information is invalid. (Of course, once we return -EINVAL for more
>> than one field, good luck figuring out which field is invalid!)
> Yeah.  I suspect this one can be dropped if EFER.NX is required for everything
> except EPT, but I didn't fully grok the problem that this was fixing, and it's
> such an esoteric case that I both don't care and am terrified of breaking some
> bizarre case.
> 

It's dating back to 2007 when EPT didn't even exist, I would just drop it.

Paolo