linux-kernel - Re: [PATCH v3 7/9] KVM: VMX: Add guest physical address check in EPT violation and misconfig

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Date:   Thu, 22 Oct 2020 20:14:33 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Mohammed Gamal <mgamal@...hat.com>, kvm list <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v3 7/9] KVM: VMX: Add guest physical address check in EPT
 violation and misconfig

On Wed, Oct 14, 2020 at 04:44:57PM -0700, Jim Mattson wrote:
> On Fri, Oct 9, 2020 at 9:17 AM Jim Mattson <jmattson@...gle.com> wrote:
> >
> > On Fri, Jul 10, 2020 at 8:48 AM Mohammed Gamal <mgamal@...hat.com> wrote:
> > > @@ -5308,6 +5314,18 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
> > >                PFERR_GUEST_FINAL_MASK : PFERR_GUEST_PAGE_MASK;
> > >
> > >         vcpu->arch.exit_qualification = exit_qualification;
> > > +
> > > +       /*
> > > +        * Check that the GPA doesn't exceed physical memory limits, as that is
> > > +        * a guest page fault.  We have to emulate the instruction here, because
> > > +        * if the illegal address is that of a paging structure, then
> > > +        * EPT_VIOLATION_ACC_WRITE bit is set.  Alternatively, if supported we
> > > +        * would also use advanced VM-exit information for EPT violations to
> > > +        * reconstruct the page fault error code.
> > > +        */
> > > +       if (unlikely(kvm_mmu_is_illegal_gpa(vcpu, gpa)))
> > > +               return kvm_emulate_instruction(vcpu, 0);
> > > +
> >
> > Is kvm's in-kernel emulator up to the task? What if the instruction in
> > question is AVX-512, or one of the myriad instructions that the
> > in-kernel emulator can't handle? Ice Lake must support the advanced
> > VM-exit information for EPT violations, so that would seem like a
> > better choice.
> >
> Anyone?

Using "advanced info" if it's supported seems like the way to go.  Outright
requiring it is probably overkill; if userspace wants to risk having to kill a
(likely broken) guest, so be it.