Re: [PATCH v16 Kernel 5/7] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap

[Yan Zhao]

On Wed, Mar 25, 2020 at 03:32:37AM +0800, Kirti Wankhede 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 <address@hidden>
> Reviewed-by: Neo Jia <address@hidden>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 54 
> ++++++++++++++++++++++++++++++++++++++---
>  include/uapi/linux/vfio.h       | 10 ++++++++
>  2 files changed, 60 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 27ed069c5053..b98a8d79e13a 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -982,7 +982,8 @@ 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;
> @@ -1033,6 +1034,10 @@ 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);
> @@ -1040,6 +1045,13 @@ 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->iova != unmap->iova || dma->size != unmap->size)) {
potential NULL pointer!

And could you address the comments in v14?
How to handle DSI unmaps in vIOMMU
(https://lore.kernel.org/kvm/20200323011041.GB5456@joy-OptiPlex-7040/)

> +                     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;
> @@ -1057,6 +1069,11 @@ 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;
>  
> @@ -2418,17 +2435,46 @@ 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;
> +                     uint64_t iommu_pgsize =
> +                                      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 0018721fb744..7c888041136f 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -1011,12 +1011,22 @@ 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)
> -- 
> 2.7.0
>