[+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. > >> 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. > > 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 _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
