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

[Kirti Wankhede]

On 3/31/2020 3:04 AM, Alex Williamson wrote:
> On Mon, 30 Mar 2020 22:20:42 +0530
> Kirti Wankhede <address@hidden> 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 | 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,


Yes, updating check.

Is !dma here also error case when VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP 
flag is not set?
DMA_UNMAP ioctl returns how much was unmapped, from user space 
perspective this would be from start of range (unmap->iova), right?

Thanks,
Kirti