On Mon, 18 Jan 2021 20:25:09 +0800
Keqian Zhu [off-list ref] wrote:

On 2021/1/16 2:01, Alex Williamson wrote:

quoted

On Fri, 15 Jan 2021 17:26:42 +0800
Keqian Zhu [off-list ref] wrote:
  

quoted

If a group with non-pinned-page dirty scope is detached with dirty
logging enabled, we should fully populate the dirty bitmaps at the
time it's removed since we don't know the extent of its previous DMA,
nor will the group be present to trigger the full bitmap when the user
retrieves the dirty bitmap.

Fixes: d6a4c185660c ("vfio iommu: Implementation of ioctl for dirty pages tracking")
Suggested-by: Alex Williamson <redacted>
Signed-off-by: Keqian Zhu <redacted>
---
 drivers/vfio/vfio_iommu_type1.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 0b4dedaa9128..4e82b9a3440f 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c

@@ -236,6 +236,19 @@ static void vfio_dma_populate_bitmap(struct vfio_dma *dma, size_t pgsize)
 	}
 }
 
+static void vfio_iommu_populate_bitmap_full(struct vfio_iommu *iommu)
+{
+	struct rb_node *n;
+	unsigned long pgshift = __ffs(iommu->pgsize_bitmap);
+
+	for (n = rb_first(&iommu->dma_list); n; n = rb_next(n)) {
+		struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
+
+		if (dma->iommu_mapped)
+			bitmap_set(dma->bitmap, 0, dma->size >> pgshift);
+	}
+}
+
 static int vfio_dma_bitmap_alloc_all(struct vfio_iommu *iommu, size_t pgsize)
 {
 	struct rb_node *n;

@@ -2415,8 +2428,11 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
 	 * Removal of a group without dirty tracking may allow the iommu scope
 	 * to be promoted.
 	 */
-	if (update_dirty_scope)
+	if (update_dirty_scope) {
 		update_pinned_page_dirty_scope(iommu);
+		if (iommu->dirty_page_tracking)
+			vfio_iommu_populate_bitmap_full(iommu);
+	}
 	mutex_unlock(&iommu->lock);
 }
   

This doesn't do the right thing.  This marks the bitmap dirty if:

 * The detached group dirty scope was not limited to pinned pages

 AND

 * Dirty tracking is enabled

 AND

 * The vfio_dma is *currently* (ie. after the detach) iommu_mapped

We need to mark the bitmap dirty based on whether the vfio_dma *was*
iommu_mapped by the group that is now detached.  Thanks,

Alex
  

Hi Alex,

Yes, I missed this point again :-(. The update_dirty_scope means we
detached an iommu backed group, and that means the vfio_dma *was*
iommu_mapped by this group, so we can populate full bitmap
unconditionally, right?

To do it unconditionally, the assumption would be that all current
vfio_dmas are iommu_mapped.  It seems like it's deterministic that a
non-pinned-page scope group implies all vfio_dmas are iommu_mapped.  I
can't currently think of an exception.  Thanks,

Alex


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel