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Re: [PATCH v17 Kernel 5/7] vfio iommu: Update UNMAP_DMA ioctl to get dir

From: Kirti Wankhede
Subject: Re: [PATCH v17 Kernel 5/7] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap
Date: Wed, 1 Apr 2020 00:16:13 +0530
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0

On 3/31/2020 3:04 AM, Alex Williamson wrote:
On Mon, 30 Mar 2020 22:20:42 +0530
Kirti Wankhede <address@hidden> wrote:

DMA mapped pages, including those pinned by mdev vendor drivers, might
get unpinned and unmapped while migration is active and device is still
running. For example, in pre-copy phase while guest driver could access
those pages, host device or vendor driver can dirty these mapped pages.
Such pages should be marked dirty so as to maintain memory consistency
for a user making use of dirty page tracking.

To get bitmap during unmap, user should allocate memory for bitmap, set
size of allocated memory, set page size to be considered for bitmap and

Signed-off-by: Kirti Wankhede <address@hidden>
Reviewed-by: Neo Jia <address@hidden>
  drivers/vfio/vfio_iommu_type1.c | 55 ++++++++++++++++++++++++++++++++++++++---
  include/uapi/linux/vfio.h       | 10 ++++++++
  2 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 5efebc2b60e1..266550bd7307 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -983,7 +983,8 @@ static int verify_bitmap_size(uint64_t npages, uint64_t 
static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
-                            struct vfio_iommu_type1_dma_unmap *unmap)
+                            struct vfio_iommu_type1_dma_unmap *unmap,
+                            struct vfio_bitmap *bitmap)
        uint64_t mask;
        struct vfio_dma *dma, *dma_last = NULL;
@@ -1034,6 +1035,10 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
         * will be returned if these conditions are not met.  The v2 interface
         * will only return success and a size of zero if there were no
         * mappings within the range.
+        *
+        * When VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP flag is set, unmap request
+        * must be for single mapping. Multiple mappings with this flag set is
+        * not supported.
        if (iommu->v2) {
                dma = vfio_find_dma(iommu, unmap->iova, 1);
@@ -1041,6 +1046,14 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
                        ret = -EINVAL;
                        goto unlock;
+               if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
+                   dma &&
+                   (dma->iova != unmap->iova || dma->size != unmap->size)) {

I think your intention was to return error if the user asked for the
dirty bitmap and the requested unmap range doesn't exactly match the
vfio_dma.  Not finding a vfio_dma should therefore also be an error.
For example, if we had a single mapping at {0x1000-0x1fff} and the user
unmapped with dirty bitmap {0x0-0x2fff}, that should return an error,
but it's not caught by the above because there is no vfio_dma @0x0.
Therefore I think you want:

  (!dma || dma->iova != unmap->iova || dma->size != unmap->size))

Right?  Thanks,

Yes, updating check.

Is !dma here also error case when VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP flag is not set? DMA_UNMAP ioctl returns how much was unmapped, from user space perspective this would be from start of range (unmap->iova), right?


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