Re: [PATCH v11 Kernel 4/6] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap

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

On Tue, 17 Dec 2019 22:40:49 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> Pages, pinned by external interface for requested IO virtual address
> range,  might get unpinned  and unmapped while migration is active and
> device is still running, that is, in pre-copy phase while guest driver
> still could access those pages. Host device can write to these pages while
> those were mapped. Such pages should be marked dirty so that after
> migration guest driver should still be able to complete the operation.
> 
> To get bitmap during unmap, user should set flag
> VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP, bitmap memory should be allocated and
> zeroed by user space application. Bitmap size and page size should be set
> by user application.
> 
> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> Reviewed-by: Neo Jia <cjia@nvidia.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 63 ++++++++++++++++++++++++++++++++++++-----
>  include/uapi/linux/vfio.h       | 12 ++++++++
>  2 files changed, 68 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 215aecb25453..101c2b1e72b4 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -974,7 +974,8 @@ static long verify_bitmap_size(unsigned long npages, unsigned long 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,
> +			     unsigned long *bitmap)
>  {
>  	uint64_t mask;
>  	struct vfio_dma *dma, *dma_last = NULL;
> @@ -1049,6 +1050,15 @@ 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) &&
> +		    (dma_last != dma))
> +			vfio_iova_dirty_bitmap(iommu, dma->iova, dma->size,
> +					     unmap->bitmap_pgsize, unmap->iova,
> +					     bitmap);
> +		else
> +			vfio_remove_unpinned_from_pfn_list(dma, true);
> +
> +
>  		if (!RB_EMPTY_ROOT(&dma->pfn_list)) {
>  			struct vfio_iommu_type1_dma_unmap nb_unmap;
>  
> @@ -1074,6 +1084,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>  						    &nb_unmap);
>  			goto again;
>  		}
> +
>  		unmapped += dma->size;
>  		vfio_remove_dma(iommu, dma);
>  	}
> @@ -2404,22 +2415,60 @@ 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;
> +		unsigned long *bitmap = NULL;
> +		long ret, bsize;
>  
>  		minsz = offsetofend(struct vfio_iommu_type1_dma_unmap, size);
>  
> -		if (copy_from_user(&unmap, (void __user *)arg, minsz))
> +		if (copy_from_user(&unmap, (void __user *)arg, sizeof(unmap)))

If we only require minsz, how are we going to copy sizeof(unmap)?  This
breaks existing userspace.  You'll need to copy the remainder of the
user data after validating that they've provided it.

>  			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 = __ffs(unmap.bitmap_pgsize);
> +			uint64_t iommu_pgmask =
> +			 ((uint64_t)1 << __ffs(vfio_pgsize_bitmap(iommu))) - 1;
> +
> +			if (((unmap.bitmap_pgsize - 1) & iommu_pgmask) !=
> +			     (unmap.bitmap_pgsize - 1))
> +				return -EINVAL;
> +
> +			bsize = verify_bitmap_size(unmap.size >> pgshift,
> +						   unmap.bitmap_size);
> +			if (bsize < 0)
> +				return bsize;
> +
> +			bitmap = kmalloc(bsize, GFP_KERNEL);

Same allocation that we cannot do.  Thanks,

Alex

> +			if (!bitmap)
> +				return -ENOMEM;
> +
> +			if (copy_from_user(bitmap, (void __user *)unmap.bitmap,
> +					   bsize)) {
> +				ret = -EFAULT;
> +				goto unmap_exit;
> +			}
> +		}
> +
> +		ret = vfio_dma_do_unmap(iommu, &unmap, bitmap);
>  		if (ret)
> -			return ret;
> +			goto unmap_exit;
>  
> -		return copy_to_user((void __user *)arg, &unmap, minsz) ?
> +		if (unmap.flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) {
> +			if (copy_to_user((void __user *)unmap.bitmap, bitmap,
> +					  bsize)) {
> +				ret = -EFAULT;
> +				goto unmap_exit;
> +			}
> +		}
> +
> +		ret = copy_to_user((void __user *)arg, &unmap, minsz) ?
>  			-EFAULT : 0;
> +unmap_exit:
> +		kfree(bitmap);
> +		return ret;
>  	} else if (cmd == VFIO_IOMMU_DIRTY_PAGES) {
>  		struct vfio_iommu_type1_dirty_bitmap range;
>  		uint32_t mask = VFIO_IOMMU_DIRTY_PAGES_FLAG_START |
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 8268634e7e08..e8e044c4974d 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -964,12 +964,24 @@ struct vfio_iommu_type1_dma_map {
>   * 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 should
> + * allocate memory to get bitmap, clear the bitmap memory by setting zero and
> + * should set size of allocated memory in bitmap_size field. One bit in bitmap
> + * represents per page , page of user provided page size in 'bitmap_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 bitmap.
>   */
>  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) */
> +	__u64        bitmap_pgsize;		/* page size for bitmap */
> +	__u64        bitmap_size;               /* in bytes */
> +	void __user *bitmap;                    /* one bit per page */
>  };
>  
>  #define VFIO_IOMMU_UNMAP_DMA _IO(VFIO_TYPE, VFIO_BASE + 14)