Re: [PATCH v3 2/5] intel_iommu: Fix a potential issue in VFIO dirty page sync

[Peter Xu <peterx@redhat.com>]

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>

-- 
Peter Xu