| Message ID | 20230608095231.225450-3-zhenzhong.duan@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Optimize UNMAP call and bug fix | expand |
On Thu, Jun 08, 2023 at 05:52:28PM +0800, Zhenzhong Duan wrote: > Peter Xu found a potential issue: > > "The other thing is when I am looking at the new code I found that we > actually extended the replay() to be used also in dirty tracking of vfio, > in vfio_sync_dirty_bitmap(). For that maybe it's already broken if > unmap_all() because afaiu log_sync() can be called in migration thread > anytime during DMA so I think it means the device is prone to DMA with the > IOMMU pgtable quickly erased and rebuilt here, which means the DMA could > fail unexpectedly. Copy Alex, Kirti and Neo." > > Fix it by replacing the unmap_all() to only evacuate the iova tree > (keeping all host mappings untouched, IOW, don't notify UNMAP), and > do a full resync in page walk which will notify all existing mappings > as MAP. This way we don't interrupt with any existing mapping if there > is (e.g. for the dirty sync case), meanwhile we keep sync too to latest > (for moving a vfio device into an existing iommu group). > > Suggested-by: Peter Xu <peterx@redhat.com> > Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com> Reviewed-by: Peter Xu <peterx@redhat.com>
diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c index 94d52f4205d2..34af12f392f5 100644 --- a/hw/i386/intel_iommu.c +++ b/hw/i386/intel_iommu.c @@ -3825,13 +3825,10 @@ static void vtd_iommu_replay(IOMMUMemoryRegion *iommu_mr, IOMMUNotifier *n) IntelIOMMUState *s = vtd_as->iommu_state; uint8_t bus_n = pci_bus_num(vtd_as->bus); VTDContextEntry ce; + DMAMap map = { .iova = 0, .size = HWADDR_MAX }; - /* - * The replay can be triggered by either a invalidation or a newly - * created entry. No matter what, we release existing mappings - * (it means flushing caches for UNMAP-only registers). - */ - vtd_address_space_unmap(vtd_as, n); + /* replay is protected by BQL, page walk will re-setup it safely */ + iova_tree_remove(vtd_as->iova_tree, map); if (vtd_dev_to_context_entry(s, bus_n, vtd_as->devfn, &ce) == 0) { trace_vtd_replay_ce_valid(s->root_scalable ? "scalable mode" :
Peter Xu found a potential issue: "The other thing is when I am looking at the new code I found that we actually extended the replay() to be used also in dirty tracking of vfio, in vfio_sync_dirty_bitmap(). For that maybe it's already broken if unmap_all() because afaiu log_sync() can be called in migration thread anytime during DMA so I think it means the device is prone to DMA with the IOMMU pgtable quickly erased and rebuilt here, which means the DMA could fail unexpectedly. Copy Alex, Kirti and Neo." Fix it by replacing the unmap_all() to only evacuate the iova tree (keeping all host mappings untouched, IOW, don't notify UNMAP), and do a full resync in page walk which will notify all existing mappings as MAP. This way we don't interrupt with any existing mapping if there is (e.g. for the dirty sync case), meanwhile we keep sync too to latest (for moving a vfio device into an existing iommu group). Suggested-by: Peter Xu <peterx@redhat.com> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com> --- hw/i386/intel_iommu.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-)