Re: [PATCH v14 Kernel 5/7] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap

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

On Fri, 20 Mar 2020 04:35:29 -0400
Yan Zhao <yan.y.zhao@intel.com> wrote:

> On Thu, Mar 19, 2020 at 03:41:12AM +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 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 | 55 ++++++++++++++++++++++++++++++++++++++---
> >  include/uapi/linux/vfio.h       | 11 +++++++++
> >  2 files changed, 62 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > index d6417fb02174..aa1ac30f7854 100644
> > --- a/drivers/vfio/vfio_iommu_type1.c
> > +++ b/drivers/vfio/vfio_iommu_type1.c
> > @@ -939,7 +939,8 @@ 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;
> > @@ -990,6 +991,10 @@ 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);
> > @@ -997,6 +1002,13 @@ 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)) {  
> dma is probably NULL here!

Yep, I didn't look closely enough there.  This is situated right
between the check to make sure we're not bisecting a mapping at the
start of the unmap and the check to make sure we're not bisecting a
mapping at the end of the unmap.  There's no guarantee that we have a
valid pointer here.  The test should be in the while() loop below this
code.

> And this restriction on UNMAP would make some UNMAP operations of vIOMMU
> fail.
> 
> e.g. below condition indeed happens in reality.
> an UNMAP ioctl comes for IOVA range from 0xff800000, of size 0x200000
> However, IOVAs in this range are mapped page by page.i.e., dma->size is 0x1000.
> 
> Previous, this UNMAP ioctl could unmap successfully as a whole.

What triggers this in the guest?  Note that it's only when using the
GET_DIRTY_BITMAP flag that this is restricted.  Does the event you're
referring to potentially occur under normal circumstances in that mode?
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;
> > @@ -1014,6 +1026,12 @@ 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,
> > +					(unsigned char __user *) bitmap->data);
> > +
> >  		if (!RB_EMPTY_ROOT(&dma->pfn_list)) {
> >  			struct vfio_iommu_type1_dma_unmap nb_unmap;
> >  
> > @@ -2369,17 +2387,46 @@ 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 043e9eafb255..a704e5380f04 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -1010,12 +1010,23 @@ 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, clear the bitmap memory by setting zero and must set size of
> > + * allocated memory in vfio_bitmap.size field. One bit in bitmap
> > + * represents per page, 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
> >   
>