Re: [PATCH v17 Kernel 5/7] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 30 Mar 2020 22:20:42 +0530
Kirti Wankhede <kwankhede@nvidia.com> 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
> set flag VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP.
> 
> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> Reviewed-by: Neo Jia <cjia@nvidia.com>
> ---
>  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 bitmap_size)
>  }
>  
>  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:

((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
 (!dma || dma->iova != unmap->iova || dma->size != unmap->size))

Right?  Thanks,

Alex


> +			ret = -EINVAL;
> +			goto unlock;
> +		}
> +
>  		dma = vfio_find_dma(iommu, unmap->iova + unmap->size - 1, 0);
>  		if (dma && dma->iova + dma->size != unmap->iova + unmap->size) {
>  			ret = -EINVAL;
> @@ -1058,6 +1071,11 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>  		if (dma->task->mm != current->mm)
>  			break;
>  
> +		if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
> +		     iommu->dirty_page_tracking)
> +			vfio_iova_dirty_bitmap(iommu, dma->iova, dma->size,
> +						bitmap->pgsize, bitmap->data);
> +
>  		if (!RB_EMPTY_ROOT(&dma->pfn_list)) {
>  			struct vfio_iommu_type1_dma_unmap nb_unmap;
>  
> @@ -2419,17 +2437,46 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>  
>  	} else if (cmd == VFIO_IOMMU_UNMAP_DMA) {
>  		struct vfio_iommu_type1_dma_unmap unmap;
> -		long ret;
> +		struct vfio_bitmap bitmap = { 0 };
> +		int ret;
>  
>  		minsz = offsetofend(struct vfio_iommu_type1_dma_unmap, size);
>  
>  		if (copy_from_user(&unmap, (void __user *)arg, minsz))
>  			return -EFAULT;
>  
> -		if (unmap.argsz < minsz || unmap.flags)
> +		if (unmap.argsz < minsz ||
> +		    unmap.flags & ~VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP)
>  			return -EINVAL;
>  
> -		ret = vfio_dma_do_unmap(iommu, &unmap);
> +		if (unmap.flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) {
> +			unsigned long pgshift;
> +			size_t iommu_pgsize =
> +				(size_t)1 << __ffs(vfio_pgsize_bitmap(iommu));
> +
> +			if (unmap.argsz < (minsz + sizeof(bitmap)))
> +				return -EINVAL;
> +
> +			if (copy_from_user(&bitmap,
> +					   (void __user *)(arg + minsz),
> +					   sizeof(bitmap)))
> +				return -EFAULT;
> +
> +			/* allow only min supported pgsize */
> +			if (bitmap.pgsize != iommu_pgsize)
> +				return -EINVAL;
> +			if (!access_ok((void __user *)bitmap.data, bitmap.size))
> +				return -EINVAL;
> +
> +			pgshift = __ffs(bitmap.pgsize);
> +			ret = verify_bitmap_size(unmap.size >> pgshift,
> +						 bitmap.size);
> +			if (ret)
> +				return ret;
> +
> +		}
> +
> +		ret = vfio_dma_do_unmap(iommu, &unmap, &bitmap);
>  		if (ret)
>  			return ret;
>  
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 5f359c63f5ef..e3cbf8b78623 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -1048,12 +1048,22 @@ struct vfio_bitmap {
>   * field.  No guarantee is made to the user that arbitrary unmaps of iova
>   * or size different from those used in the original mapping call will
>   * succeed.
> + * VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP should be set to get dirty bitmap
> + * before unmapping IO virtual addresses. When this flag is set, user must
> + * provide data[] as structure vfio_bitmap. User must allocate memory to get
> + * bitmap and must set size of allocated memory in vfio_bitmap.size field.
> + * A bit in bitmap represents one page of user provided page size in 'pgsize',
> + * consecutively starting from iova offset. Bit set indicates page at that
> + * offset from iova is dirty. Bitmap of pages in the range of unmapped size is
> + * returned in vfio_bitmap.data
>   */
>  struct vfio_iommu_type1_dma_unmap {
>  	__u32	argsz;
>  	__u32	flags;
> +#define VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP (1 << 0)
>  	__u64	iova;				/* IO virtual address */
>  	__u64	size;				/* Size of mapping (bytes) */
> +	__u8    data[];
>  };
>  
>  #define VFIO_IOMMU_UNMAP_DMA _IO(VFIO_TYPE, VFIO_BASE + 14)