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    SubjectRe: [PATCH 0/2] KVM: MMU: support VMAs that got remap_pfn_range-ed
    On Wed, 6 Jul 2016 08:05:15 +0200
    Paolo Bonzini <pbonzini@redhat.com> wrote:

    > On 06/07/2016 04:00, Xiao Guangrong wrote:
    > >
    > >
    > > On 07/05/2016 08:18 PM, Paolo Bonzini wrote:
    > >>
    > >>
    > >> On 05/07/2016 07:41, Neo Jia wrote:
    > >>> On Thu, Jun 30, 2016 at 03:01:49PM +0200, Paolo Bonzini wrote:
    > >>>> The vGPU folks would like to trap the first access to a BAR by setting
    > >>>> vm_ops on the VMAs produced by mmap-ing a VFIO device. The fault
    > >>>> handler
    > >>>> then can use remap_pfn_range to place some non-reserved pages in the
    > >>>> VMA.
    > >>>>
    > >>>> KVM lacks support for this kind of non-linear VM_PFNMAP mapping, and
    > >>>> these
    > >>>> patches should fix this.
    > >>>
    > >>> Hi Paolo,
    > >>>
    > >>> I have tested your patches with the mediated passthru patchset that
    > >>> is being
    > >>> reviewed in KVM and QEMU mailing list.
    > >>>
    > >>> The fault handler gets called successfully and the previously mapped
    > >>> memory gets
    > >>> unmmaped correctly via unmap_mapping_range.
    > >>
    > >> Great, then I'll include them in 4.8.
    > >
    > > Code is okay, but i still suspect if this implementation, fetch mmio
    > > pages in fault handler, is needed. We'd better include these patches
    > > after the design of vfio framework is decided.
    >
    > I think that this fixes a bug anyway, the previous handling of VM_PFNMAP
    > is too simplistic.


    Agreed, no reason to hold off on this, it's a valid interaction that
    needs to be fixed regardless of how or if the vfio mediated driver
    makes use of it. Thanks,

    Alex

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