From: Jim Mattson <jmattson@google.com>
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>
Subject: Re: [PATCH v3 7/9] KVM: VMX: Add guest physical address check in EPT violation and misconfig
Date: Fri, 23 Oct 2020 09:59:03 -0700 [thread overview]
Message-ID: <CALMp9eQ8C0pp5yP4tLsckVWq=j3Xb=e4M7UVZz67+pngaXJJUw@mail.gmail.com> (raw)
In-Reply-To: <498cfe12-f3e4-c4a2-f36b-159ccc10cdc4@redhat.com>
On Fri, Oct 23, 2020 at 2:22 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 23/10/20 05:14, Sean Christopherson wrote:
> >>>> +
> >>>> + /*
> >>>> + * 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.
>
> Yeah, the instruction is expected to page-fault here. However the
> comment is incorrect and advanced information does not help here.
>
> 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 in-kernel emulator should
only be used as a last resort on hardware that doesn't support the
advanced VM-exit information for EPT violations.
next prev parent reply other threads:[~2020-10-23 16:59 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-10 15:48 [PATCH v3 0/9] KVM: Support guest MAXPHYADDR < host MAXPHYADDR Mohammed Gamal
2020-07-10 15:48 ` [PATCH v3 1/9] KVM: x86: Add helper functions for illegal GPA checking and page fault injection Mohammed Gamal
2020-07-10 15:48 ` [PATCH v3 2/9] KVM: x86: mmu: Move translate_gpa() to mmu.c Mohammed Gamal
2020-07-10 15:48 ` [PATCH v3 3/9] KVM: x86: mmu: Add guest physical address check in translate_gpa() Mohammed Gamal
2020-07-10 17:41 ` Paolo Bonzini
2020-07-10 15:48 ` [PATCH v3 4/9] KVM: x86: rename update_bp_intercept to update_exception_bitmap Mohammed Gamal
2020-07-10 16:15 ` Jim Mattson
2020-07-10 15:48 ` [PATCH v3 5/9] KVM: x86: update exception bitmap on CPUID changes Mohammed Gamal
2020-07-10 16:25 ` Jim Mattson
2020-07-10 15:48 ` [PATCH v3 6/9] KVM: VMX: introduce vmx_need_pf_intercept Mohammed Gamal
2020-07-10 15:48 ` [PATCH v3 7/9] KVM: VMX: Add guest physical address check in EPT violation and misconfig Mohammed Gamal
2020-07-13 18:32 ` Sean Christopherson
2020-07-15 23:00 ` Sean Christopherson
2020-08-17 17:22 ` Sean Christopherson
2020-08-17 18:01 ` Paolo Bonzini
2020-10-09 16:17 ` Jim Mattson
2020-10-14 23:44 ` Jim Mattson
2020-10-23 3:14 ` Sean Christopherson
2020-10-23 9:22 ` Paolo Bonzini
2020-10-23 16:59 ` Jim Mattson [this message]
2020-10-23 17:16 ` Paolo Bonzini
2020-10-23 17:23 ` Jim Mattson
2020-10-23 17:43 ` Paolo Bonzini
2021-01-15 19:35 ` Jim Mattson
2021-01-20 21:16 ` Jim Mattson
2021-01-27 20:57 ` Jim Mattson
2021-06-21 18:31 ` Jim Mattson
2020-07-10 15:48 ` [PATCH v3 8/9] KVM: VMX: optimize #PF injection when MAXPHYADDR does not match Mohammed Gamal
2020-07-10 15:48 ` [PATCH v3 9/9] KVM: x86: SVM: VMX: Make GUEST_MAXPHYADDR < HOST_MAXPHYADDR support configurable Mohammed Gamal
2020-07-10 17:40 ` Paolo Bonzini
2020-07-10 16:30 ` [PATCH v3 0/9] KVM: Support guest MAXPHYADDR < host MAXPHYADDR Jim Mattson
2020-07-10 17:06 ` Paolo Bonzini
2020-07-10 17:13 ` Jim Mattson
2020-07-10 17:16 ` Paolo Bonzini
2020-07-10 17:26 ` Sean Christopherson
2020-07-10 17:26 ` Jim Mattson
2020-07-10 17:40 ` Paolo Bonzini
2020-07-10 17:49 ` Paolo Bonzini
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