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SubjectRe: [PATCH v4 05/22] iommu: introduce iommu invalidate API function
On Thu, 3 May 2018 21:46:16 -0700
Jacob Pan <jacob.jun.pan@linux.intel.com> wrote:

> On Wed, 2 May 2018 10:31:50 +0100
> Jean-Philippe Brucker <jean-philippe.brucker@arm.com> wrote:
>
> > 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.
> >
> Sorry for the delay but you are right, I have also confirmed with Yi
> that we don't need second level invalidation. I will remove IOTLB
> invalidation w/o PASID case from the API.
>
Now the passdown invalidation granularities look like:
(sorted by coarseness), will send out in v5 patchset soon if no issues.

/**
* enum iommu_inv_granularity - Generic invalidation granularity
*
* @IOMMU_INV_GRANU_DOMAIN: Device context cache associated with a
* domain ID.
* @IOMMU_INV_GRANU_DEVICE: Device context cache associated with a
* device ID
* @IOMMU_INV_GRANU_DOMAIN_ALL_PASID: TLB entries or PASID caches of all
* PASIDs associated with a domain ID
* @IOMMU_INV_GRANU_PASID_SEL: TLB entries or PASID cache associated
* with a PASID and a domain
* @IOMMU_INV_GRANU_PAGE_PASID: TLB entries of selected page range
* within a PASID
*
* When an invalidation request is passed down to IOMMU to flush translation
* caches, it may carry different granularity levels, which can be specific
* to certain types of translation caches. For an example, PASID selective
* granularity is only applicable PASID cache and IOTLB invalidation but for
* device context caches.
* This enum is a collection of granularities for all types of translation
* caches. The idea is to make it easy for IOMMU model specific driver to
* convert from generic to model specific value. Not all combinations between
* translation caches and granularity levels are valid. Each IOMMU driver
* can enforce check based on its own conversion table. The conversion is
* based on 2D look-up with inputs as follows:
* - translation cache types
* - granularity
* No global granularity is allowed in that passdown invalidation for an
* assigned device should only impact the device or domain itself.
*
* type | DTLB | TLB | PASID | CONTEXT
* granule | | | |
* -----------------+-----------+-----------+-----------+-----------
* DOMAIN | | | | Y
* DEVICE | | | | Y
* DN_ALL_PASID | Y | Y | Y |
* PASID_SEL | Y | Y | Y |
* PAGE_PASID | | Y | |
*
*/
enum iommu_inv_granularity {
IOMMU_INV_GRANU_DOMAIN,
IOMMU_INV_GRANU_DEVICE,
IOMMU_INV_GRANU_DOMAIN_ALL_PASID,
IOMMU_INV_GRANU_PASID_SEL,
IOMMU_INV_GRANU_PAGE_PASID,
IOMMU_INV_NR_GRANU,
};


> Thanks,
>
> > Thanks,
> > Jean
> >
>
> [Jacob Pan]

[Jacob Pan]

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