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    SubjectRe: [PATCH v4 05/22] iommu: introduce iommu invalidate API function
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    On 01/05/18 23:58, Jacob Pan wrote:
    >>>> Maybe this should be called "NG_PAGE_PASID",
    >>> Sure. I was thinking page range already implies non-global pages.
    >>>> and "DOMAIN_PAGE" should
    >>>> instead be "PAGE_PASID". If I understood their meaning correctly,
    >>>> it would be more consistent with the rest.
    >>>>
    >>> I am trying not to mix granu between request w/ PASID and w/o.
    >>> DOMAIN_PAGE meant to be for request w/o PASID.
    >>
    >> Is the distinction necessary? I understand the IOMMU side might offer
    >> many possibilities for invalidation, but the user probably doesn't
    >> need all of them. It might be easier to document, upstream and
    >> maintain if we only specify what's currently needed by users (what
    >> does QEMU VT-d use?) Others can always extend it by increasing the
    >> version.
    >>
    >> Do you think that this invalidation message will be used outside of
    >> BIND_PASID_TABLE context? I can't see an other use but who knows. At
    >> the moment requests w/o PASID are managed with
    >> VFIO_IOMMU_MAP/UNMAP_DMA, which doesn't require invalidation. And in
    >> a BIND_PASID_TABLE context, IOMMUs requests w/o PASID are just a
    >> special case using PASID 0 (for Arm and AMD) so I suppose they'll use
    >> the same invalidation commands as requests w/ PASID.
    >>
    > My understanding is that for GIOVA use case, VT-d vIOMMU creates
    > GIOVA-GPA mapping and the host shadows the 2nd level page tables to
    > create GIOVA-HPA mapping. So when assigned device in the guest can do
    > both DMA map/unmap and VFIO map/unmap, VFIO unmap is one time deal
    > (I guess invalidation can be captured in other code path), but guest
    > kernel use of DMA unmap could will trigger invalidation. QEMU needs to
    > trap those invalidation and passdown to physical IOMMU. So we do need
    > invalidation w/o PASID.

    Hm, isn't this all done by host userspace? Whether guest does DMA
    map/unmap or VFIO map/unmap, it creates/removes IOVA-GPA mappings in the
    vIOMMU. QEMU captures invalidation requests for these mappings from the
    guest, finds GPA-HVA in the shadow map and sends a VFIO map/unmap
    request for IOVA-HVA.

    Thanks,
    Jean

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