> From: Xiang Zheng > Sent: Monday, May 25, 2020 7:34 PM > > [+cc Kirti, Yan, Alex] > > On 2020/5/23 1:14, Jean-Philippe Brucker wrote: > > Hi, > > > > On Tue, May 19, 2020 at 05:42:55PM +0800, Xiang Zheng wrote: > >> Hi all, > >> > >> Is there any plan for enabling SMMU HTTU? > > > > Not outside of SVA, as far as I know. > > > > >> I have seen the patch locates in the SVA series patch, which adds > >> support for HTTU: > >> https://www.spinics.net/lists/arm-kernel/msg798694.html > >> > >> HTTU reduces the number of access faults on SMMU fault queue > >> (permission faults also benifit from it). > >> > >> Besides reducing the faults, HTTU also helps to track dirty pages for > >> device DMA. Is it feasible to utilize HTTU to get dirty pages on device > >> DMA during VFIO live migration? > > > > As you know there is a VFIO interface for this under discussion: > > https://lore.kernel.org/kvm/1589781397-28368-1-git-send-email- > kwankhede@xxxxxxxxxx/ > > It doesn't implement an internal API to communicate with the IOMMU > driver > > about dirty pages. We plan to add such API later, e.g. to utilize A/D bit in VT-d 2nd-level page tables (Rev 3.0). > > > > >> If SMMU can track dirty pages, devices are not required to implement > >> additional dirty pages tracking to support VFIO live migration. > > > > It seems feasible, though tracking it in the device might be more > > efficient. I might have misunderstood but I think for live migration of > > the Intel NIC they trap guest accesses to the device and introspect its > > state to figure out which pages it is accessing. Does HTTU implement A/D-like mechanism in SMMU page tables, or just report dirty pages in a log buffer? Either way tracking dirty pages in IOMMU side is generic thus doesn't require device-specific tweak like in Intel NIC. Thanks kevin > > > > With HTTU I suppose (without much knowledge about live migration) that > > you'd need several new interfaces to the IOMMU drivers: > > > > * A way for VFIO to query HTTU support in the SMMU. There are some > > discussions about communicating more IOMMU capabilities through VFIO > but > > no implementation yet. When HTTU isn't supported the DIRTY_PAGES > bitmap > > would report all pages as they do now. > > > > * VFIO_IOMMU_DIRTY_PAGES_FLAG_START/STOP would clear the dirty bit > > for all VFIO mappings (which is going to take some time). There is a > > walker in io-pgtable for iova_to_phys() which could be extended. I > > suppose it's also possible to atomically switch the HA and HD bits in > > context descriptors. > > Maybe we need not switch HA and HD bits, just turn on them all the time? > > > > > * VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP would query the dirty > bit for all > > VFIO mappings. > > > > I think we need to consider the case of IOMMU dirty pages logging. We want > to test Kirti's VFIO migration patches combined with SMMU HTTU, any > suggestions? > > -- > Thanks, > Xiang > > _______________________________________________ > iommu mailing list > iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx > https://lists.linuxfoundation.org/mailman/listinfo/iommu _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
