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From:   Jim Mattson <jmattson@google.com>
Date:   Fri, 23 Oct 2020 10:23:43 -0700
Message-ID: <CALMp9eRGBiQDPr1wpAY34V=T6Jjij_iuHOX+_-QQPP=5SEw3GQ@mail.gmail.com>
Subject: Re: [PATCH v3 7/9] KVM: VMX: Add guest physical address check in EPT
 violation and misconfig
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Sean Christopherson <sean.j.christopherson@intel.com>,
        Mohammed Gamal <mgamal@redhat.com>,
        kvm list <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Joerg Roedel <joro@8bytes.org>
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On Fri, Oct 23, 2020 at 10:16 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 23/10/20 18:59, Jim Mattson wrote:
> >> The problem is that page fault error code bits cannot be reconstructed
> >> from bits 0..2 of the EPT violation exit qualification, if bit 8 is
> >> clear in the exit qualification (that is, if the access causing the EPT
> >> violation is to a paging-structure entry).  In that case bits 0..2 refer
> >> to the paging-structure access rather than to the final access.  In fact
> >> advanced information is not available at all for paging-structure access
> >> EPT violations.
> >
> > True, but the in-kernel emulator can only handle a very small subset
> > of the available instructions.
> >
> > If bit 8 is set in the exit qualification, we should use the advanced
> > VM-exit information. If it's clear, we should just do a software page
> > walk of the guest's x86 page tables.
>
> The information that we need is _not_ that provided by the advanced
> VM-exit information (or by a page walk).  If a page is neither writable
> nor executable, the advanced information doesn't say if the injected #PF
> should be a W=1 or a F=1 fault.  We need the information in bits 0..2 of
> the exit qualification for the final access, which however is not
> available for the paging-structure access.
>
Are you planning to extend the emulator, then, to support all
instructions? I'm not sure where you are going with this.