On Mon, 4 May 2020 21:28:57 +0530
Kirti Wankhede <kwankhede@xxxxxxxxxx> 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@xxxxxxxxxx>
> Reviewed-by: Neo Jia <cjia@xxxxxxxxxx>
> ---
> drivers/vfio/vfio_iommu_type1.c | 84 +++++++++++++++++++++++++++++++++++++++--
> include/uapi/linux/vfio.h | 10 +++++
> 2 files changed, 90 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 01dcb417836f..8b27faf1ec38 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -983,12 +983,14 @@ 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;
> size_t unmapped = 0;
> int ret = 0, retries = 0;
> + unsigned long *final_bitmap = NULL, *temp_bitmap = NULL;
>
> mask = ((uint64_t)1 << __ffs(vfio_pgsize_bitmap(iommu))) - 1;
>
> @@ -1041,6 +1043,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
> 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;
> @@ -1048,6 +1051,22 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
> }
> }
>
> + if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
> + iommu->dirty_page_tracking) {
Why do we even accept VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP when not
dirty page tracking rather than returning -EINVAL? It would simplify
things here to reject it at the ioctl and silently ignoring a flag is
rarely if ever the right approach.
> + final_bitmap = kvzalloc(bitmap->size, GFP_KERNEL);
> + if (!final_bitmap) {
> + ret = -ENOMEM;
> + goto unlock;
> + }
> +
> + temp_bitmap = kvzalloc(bitmap->size, GFP_KERNEL);
> + if (!temp_bitmap) {
> + ret = -ENOMEM;
> + kfree(final_bitmap);
> + goto unlock;
> + }
YIKES! So the user can instantly trigger the kernel to internally
allocate 2 x 256MB, regardless of how much they can actually map.
> + }
> +
> while ((dma = vfio_find_dma(iommu, unmap->iova, unmap->size))) {
> if (!iommu->v2 && unmap->iova > dma->iova)
> break;
> @@ -1058,6 +1077,24 @@ 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) {
> + unsigned long pgshift = __ffs(bitmap->pgsize);
> + unsigned int npages = dma->size >> pgshift;
> + unsigned int shift;
> +
> + vfio_iova_dirty_bitmap(iommu, dma->iova, dma->size,
> + bitmap->pgsize, (u64 *)temp_bitmap);
vfio_iova_dirty_bitmap() takes a __user bitmap, we're doing
copy_to_user() on a kernel allocated buffer???
> +
> + shift = (dma->iova - unmap->iova) >> pgshift;
> + if (shift)
> + bitmap_shift_left(temp_bitmap, temp_bitmap,
> + shift, npages);
> + bitmap_or(final_bitmap, final_bitmap, temp_bitmap,
> + shift + npages);
> + memset(temp_bitmap, 0, bitmap->size);
> + }
It seems like if the per vfio_dma dirty bitmap was oversized by a long
that we could shift it in place, then we'd only need one working bitmap
buffer and we could size that to fit the vfio_dma (or the largest
vfio_dma if we don't want to free and re-alloc for each vfio_dma).
We'd need to do more copy_to/from_user()s, but we'd also avoid copying
between sparse mappings (user zero'd bitmap required) and we'd have a
far more reasonable memory usage. Thanks,
Alex
> +
> if (!RB_EMPTY_ROOT(&dma->pfn_list)) {
> struct vfio_iommu_type1_dma_unmap nb_unmap;
>
> @@ -1088,6 +1125,16 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
> }
>
> unlock:
> + if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
> + iommu->dirty_page_tracking && final_bitmap) {
> + if (copy_to_user((void __user *)bitmap->data, final_bitmap,
> + bitmap->size))
> + ret = -EFAULT;
> +
> + kfree(final_bitmap);
> + kfree(temp_bitmap);
> + }
> +
> mutex_unlock(&iommu->lock);
>
> /* Report how much was unmapped */
> @@ -2419,17 +2466,46 @@ 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)
