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Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS

From Radim Krčmář <rkrcmar@redhat.com>
Newsgroups linux.kernel
Subject Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS
Date 2017-08-17 15:30 +0200
Message-ID <uft22-5re-9@gated-at.bofh.it> (permalink)
References (5 earlier) <ufcDU-2Ry-27@gated-at.bofh.it> <ufe31-3PN-43@gated-at.bofh.it> <uff8J-4vd-3@gated-at.bofh.it> <ufoYp-2Kf-1@gated-at.bofh.it> <ufrWi-4Je-23@gated-at.bofh.it>
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2017-08-17 14:14+0200, Paolo Bonzini:
> On 17/08/2017 11:00, Paolo Bonzini wrote:
> > On 17/08/2017 00:31, Michael S. Tsirkin wrote:
> >> On Wed, Aug 16, 2017 at 11:25:35PM +0200, Paolo Bonzini wrote:
> >>> Yes, I agree.  EMULTYPE_SKIP is fine because failed decoding still
> >>> causes an exception to be injected.  Maybe it's better to gate the
> >>> EMULTYPE_SKIP emulation on the exit qualification saying this is a write
> >>
> >> I thought it's already limited to writes. I agree that's a reasonable
> >> limitation in any case.
> >>
> >>> and also not a page table walk---just in case.
> >>
> >> I still don't get it, sorry. Let's assume for the sake of argument
> >> that it's a PT walk causing the MMIO access. Just why do you think
> >> that it makes sense to skip the instruction that caused the walk?
> > 
> > I think it doesn't.  I think in that case it's better to skip the fast
> > write and proceed with full emulation.

It definitely doesn't.  I think it's possible only because virtio
forbids other access types, so we assume that every access is a write
access.

> ... nope, exit qualification is just zero for EPT misconfigurations, so
> we cannot do this.

Yeah, we'd need to use EPT violation to get that information.

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Thread

[PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Paolo Bonzini <pbonzini@redhat.com> - 2017-08-16 13:30 +0200
  Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Radim Krčmář <rkrcmar@redhat.com> - 2017-08-16 14:10 +0200
    Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Paolo Bonzini <pbonzini@redhat.com> - 2017-08-16 15:40 +0200
      Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS "Michael S. Tsirkin" <mst@redhat.com> - 2017-08-16 16:10 +0200
        Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Paolo Bonzini <pbonzini@redhat.com> - 2017-08-16 16:20 +0200
    Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS David Hildenbrand <david@redhat.com> - 2017-08-17 10:20 +0200
  Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS "Michael S. Tsirkin" <mst@redhat.com> - 2017-08-16 15:00 +0200
    Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Paolo Bonzini <pbonzini@redhat.com> - 2017-08-16 15:10 +0200
      Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS "Michael S. Tsirkin" <mst@redhat.com> - 2017-08-16 15:20 +0200
        Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Paolo Bonzini <pbonzini@redhat.com> - 2017-08-16 15:40 +0200
          Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS "Michael S. Tsirkin" <mst@redhat.com> - 2017-08-16 16:10 +0200
          Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS "Michael S. Tsirkin" <mst@redhat.com> - 2017-08-16 19:00 +0200
            Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Paolo Bonzini <pbonzini@redhat.com> - 2017-08-16 19:30 +0200
              Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Radim Krčmář <rkrcmar@redhat.com> - 2017-08-16 21:10 +0200
                Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS "Michael S. Tsirkin" <mst@redhat.com> - 2017-08-16 22:00 +0200
                Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Paolo Bonzini <pbonzini@redhat.com> - 2017-08-16 23:30 +0200
                Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS "Michael S. Tsirkin" <mst@redhat.com> - 2017-08-17 00:40 +0200
                Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Paolo Bonzini <pbonzini@redhat.com> - 2017-08-17 11:10 +0200
                Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Paolo Bonzini <pbonzini@redhat.com> - 2017-08-17 14:20 +0200
                Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Radim Krčmář <rkrcmar@redhat.com> - 2017-08-17 15:30 +0200
                Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS "Michael S. Tsirkin" <mst@redhat.com> - 2017-08-17 17:20 +0200
                Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS Radim Krčmář <rkrcmar@redhat.com> - 2017-08-17 16:00 +0200
                Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS "Michael S. Tsirkin" <mst@redhat.com> - 2017-08-17 17:30 +0200
              Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS "Michael S. Tsirkin" <mst@redhat.com> - 2017-08-16 21:50 +0200

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