Re: [PATCH Kernel v21 5/8] vfio iommu: Implementation of ioctl for dirty pages tracking

[Alex Williamson]

On Sat, 16 May 2020 02:43:20 +0530
Kirti Wankhede <address@hidden> wrote:

> VFIO_IOMMU_DIRTY_PAGES ioctl performs three operations:
> - Start dirty pages tracking while migration is active
> - Stop dirty pages tracking.
> - Get dirty pages bitmap. Its user space application's responsibility to
>   copy content of dirty pages from source to destination during migration.
> 
> To prevent DoS attack, memory for bitmap is allocated per vfio_dma
> structure. Bitmap size is calculated considering smallest supported page
> size. Bitmap is allocated for all vfio_dmas when dirty logging is enabled
> 
> Bitmap is populated for already pinned pages when bitmap is allocated for
> a vfio_dma with the smallest supported page size. Update bitmap from
> pinning functions when tracking is enabled. When user application queries
> bitmap, check if requested page size is same as page size used to
> populated bitmap. If it is equal, copy bitmap, but if not equal, return
> error.
> 
> Signed-off-by: Kirti Wankhede <address@hidden>
> Reviewed-by: Neo Jia <address@hidden>
> 
> Fixed error reported by build bot by changing pgsize type from uint64_t
> to size_t.
> Reported-by: kbuild test robot <address@hidden>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 306 
> +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 300 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index de17787ffece..8b8fe171f4c2 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -72,6 +72,7 @@ struct vfio_iommu {
>       uint64_t                pgsize_bitmap;
>       bool                    v2;
>       bool                    nesting;
> +     bool                    dirty_page_tracking;
>  };
>  
>  struct vfio_domain {
> @@ -92,6 +93,7 @@ struct vfio_dma {
>       bool                    lock_cap;       /* capable(CAP_IPC_LOCK) */
>       struct task_struct      *task;
>       struct rb_root          pfn_list;       /* Ex-user pinned pfn list */
> +     unsigned long           *bitmap;
>  };
>  
>  struct vfio_group {
> @@ -126,6 +128,19 @@ struct vfio_regions {
>  #define IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)      \
>                                       (!list_empty(&iommu->domain_list))
>  
> +#define DIRTY_BITMAP_BYTES(n)        (ALIGN(n, BITS_PER_TYPE(u64)) / 
> BITS_PER_BYTE)
> +
> +/*
> + * Input argument of number of bits to bitmap_set() is unsigned integer, 
> which
> + * further casts to signed integer for unaligned multi-bit operation,
> + * __bitmap_set().
> + * Then maximum bitmap size supported is 2^31 bits divided by 2^3 bits/byte,
> + * that is 2^28 (256 MB) which maps to 2^31 * 2^12 = 2^43 (8TB) on 4K page
> + * system.
> + */
> +#define DIRTY_BITMAP_PAGES_MAX        ((u64)INT_MAX)
> +#define DIRTY_BITMAP_SIZE_MAX         
> DIRTY_BITMAP_BYTES(DIRTY_BITMAP_PAGES_MAX)
> +
>  static int put_pfn(unsigned long pfn, int prot);
>  
>  /*
> @@ -176,6 +191,74 @@ static void vfio_unlink_dma(struct vfio_iommu *iommu, 
> struct vfio_dma *old)
>       rb_erase(&old->node, &iommu->dma_list);
>  }
>  
> +
> +static int vfio_dma_bitmap_alloc(struct vfio_dma *dma, size_t pgsize)
> +{
> +     uint64_t npages = dma->size / pgsize;
> +
> +     if (npages > DIRTY_BITMAP_PAGES_MAX)
> +             return -EINVAL;
> +
> +     dma->bitmap = kvzalloc(DIRTY_BITMAP_BYTES(npages), GFP_KERNEL);
> +     if (!dma->bitmap)
> +             return -ENOMEM;
> +
> +     return 0;
> +}
> +
> +static void vfio_dma_bitmap_free(struct vfio_dma *dma)
> +{
> +     kfree(dma->bitmap);
> +     dma->bitmap = NULL;
> +}
> +
> +static void vfio_dma_populate_bitmap(struct vfio_dma *dma, size_t pgsize)
> +{
> +     struct rb_node *p;
> +
> +     for (p = rb_first(&dma->pfn_list); p; p = rb_next(p)) {
> +             struct vfio_pfn *vpfn = rb_entry(p, struct vfio_pfn, node);
> +
> +             bitmap_set(dma->bitmap, (vpfn->iova - dma->iova) / pgsize, 1);
> +     }
> +}
> +
> +static int vfio_dma_bitmap_alloc_all(struct vfio_iommu *iommu, size_t pgsize)
> +{
> +     struct rb_node *n = rb_first(&iommu->dma_list);
> +
> +     for (; n; n = rb_next(n)) {
> +             struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
> +             int ret;
> +
> +             ret = vfio_dma_bitmap_alloc(dma, pgsize);
> +             if (ret) {
> +                     struct rb_node *p = rb_prev(n);
> +
> +                     for (; p; p = rb_prev(p)) {
> +                             struct vfio_dma *dma = rb_entry(n,
> +                                                     struct vfio_dma, node);
> +
> +                             vfio_dma_bitmap_free(dma);
> +                     }
> +                     return ret;
> +             }
> +             vfio_dma_populate_bitmap(dma, pgsize);
> +     }
> +     return 0;
> +}
> +
> +static void vfio_dma_bitmap_free_all(struct vfio_iommu *iommu)
> +{
> +     struct rb_node *n = rb_first(&iommu->dma_list);
> +
> +     for (; n; n = rb_next(n)) {
> +             struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
> +
> +             vfio_dma_bitmap_free(dma);
> +     }
> +}
> +
>  /*
>   * Helper Functions for host iova-pfn list
>   */
> @@ -568,6 +651,17 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
>                       vfio_unpin_page_external(dma, iova, do_accounting);
>                       goto pin_unwind;
>               }
> +
> +             if (iommu->dirty_page_tracking) {
> +                     unsigned long pgshift = __ffs(iommu->pgsize_bitmap);
> +
> +                     /*
> +                      * Bitmap populated with the smallest supported page
> +                      * size
> +                      */
> +                     bitmap_set(dma->bitmap,
> +                                (iova - dma->iova) >> pgshift, 1);
> +             }
>       }
>  
>       ret = i;
> @@ -802,6 +896,7 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, 
> struct vfio_dma *dma)
>       vfio_unmap_unpin(iommu, dma, true);
>       vfio_unlink_dma(iommu, dma);
>       put_task_struct(dma->task);
> +     vfio_dma_bitmap_free(dma);
>       kfree(dma);
>       iommu->dma_avail++;
>  }
> @@ -829,6 +924,92 @@ static void vfio_pgsize_bitmap(struct vfio_iommu *iommu)
>       }
>  }
>  
> +static int update_user_bitmap(u64 __user *bitmap, struct vfio_dma *dma,
> +                           dma_addr_t base_iova, size_t pgsize)
> +{
> +     unsigned long pgshift = __ffs(pgsize);
> +     unsigned long nbits = dma->size >> pgshift;
> +     unsigned long bit_offset = (dma->iova - base_iova) >> pgshift;
> +     unsigned long copy_offset = bit_offset / BITS_PER_LONG;
> +     unsigned long shift = bit_offset % BITS_PER_LONG;
> +     unsigned long leftover;
> +
> +     /* mark all pages dirty if all pages are pinned and mapped. */
> +     if (dma->iommu_mapped)
> +             bitmap_set(dma->bitmap, 0, dma->size >> pgshift);
> +
> +     if (shift) {
> +             bitmap_shift_left(dma->bitmap, dma->bitmap, shift,
> +                               nbits + shift);
> +
> +             if (copy_from_user(&leftover, (u64 *)bitmap + copy_offset,
> +                                sizeof(leftover)))
> +                     return -EFAULT;
> +
> +             bitmap_or(dma->bitmap, dma->bitmap, &leftover, shift);
> +     }
> +
> +     if (copy_to_user((u64 *)bitmap + copy_offset, dma->bitmap,
> +                      DIRTY_BITMAP_BYTES(nbits + shift)))
> +             return -EFAULT;
> +
> +     return 0;
> +}
> +
> +static int vfio_iova_dirty_bitmap(u64 __user *bitmap, struct vfio_iommu 
> *iommu,
> +                               dma_addr_t iova, size_t size, size_t pgsize)
> +{
> +     struct vfio_dma *dma;
> +     unsigned long pgshift = __ffs(pgsize);
> +     int ret;
> +
> +     /*
> +      * GET_BITMAP request must fully cover vfio_dma mappings.  Multiple
> +      * vfio_dma mappings may be clubbed by specifying large ranges, but
> +      * there must not be any previous mappings bisected by the range.
> +      * An error will be returned if these conditions are not met.
> +      */
> +     dma = vfio_find_dma(iommu, iova, 1);
> +     if (dma && dma->iova != iova)
> +             return -EINVAL;
> +
> +     dma = vfio_find_dma(iommu, iova + size - 1, 0);
> +     if (dma && dma->iova + dma->size != iova + size)
> +             return -EINVAL;
> +
> +     dma = vfio_find_dma(iommu, iova, size);
> +
> +     while (dma && (dma->iova >= iova) &&
> +             (dma->iova + dma->size <= iova + size)) {

Thanks for doing this!  Unfortunately I think I've mislead you :(
But I think there was a bug here in the last version as well, so maybe
it's all for the better ;)

vfio_find_dma() does not guarantee to find the first dma in the range
(ie. the lowest iova), it only guarantees to find a dma in the range.
Since we have a tree structure, as we descend the nodes we might find
multiple nodes within the range.  vfio_find_dma() only returns the first
occurrence it finds, so we can't assume that other matching nodes are
next in the tree or that their iovas are greater than the iova of the
node we found.

All the other use cases of vfio_find_dma() are looking for specific
pages or boundaries or checking for the existence of a conflict or are
removing all of the instances within the range, which is probably the
example that was used in the v20 version of this patch, since it was
quite similar to vfio_dma_do_unmap() but tried to adjust the size to
get the next match rather than removing the entry.  That could
potentially lead to an entire unexplored half of the tree making our
bitmap incomplete.

So I think my initial suggestion[1] on the previous version is probably
the way we should go.  Sorry!  OTOH, it would have been a nasty bug to
find later, it's a subtle semantic that's easy to overlook.  Thanks,

Alex

[1]https://lore.kernel.org/kvm/address@hidden/

> +             struct rb_node *n;
> +
> +             ret = update_user_bitmap(bitmap, dma, iova, pgsize);
> +             if (ret)
> +                     return ret;
> +
> +             /*
> +              * Re-populate bitmap to include all pinned pages which are
> +              * considered as dirty but exclude pages which are unpinned and
> +              * pages which are marked dirty by vfio_dma_rw()
> +              */
> +             bitmap_clear(dma->bitmap, 0, dma->size >> pgshift);
> +             vfio_dma_populate_bitmap(dma, pgsize);
> +
> +             n = rb_next(&dma->node);
> +             dma = rb_entry(n, struct vfio_dma, node);
> +     }
> +     return 0;
> +}
> +
> +static int verify_bitmap_size(uint64_t npages, uint64_t bitmap_size)
> +{
> +     if (!npages || !bitmap_size || (bitmap_size > DIRTY_BITMAP_SIZE_MAX) ||
> +         (bitmap_size < DIRTY_BITMAP_BYTES(npages)))
> +             return -EINVAL;
> +
> +     return 0;
> +}
> +
>  static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>                            struct vfio_iommu_type1_dma_unmap *unmap)
>  {
> @@ -1046,7 +1227,7 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>       unsigned long vaddr = map->vaddr;
>       size_t size = map->size;
>       int ret = 0, prot = 0;
> -     uint64_t mask;
> +     size_t pgsize;
>       struct vfio_dma *dma;
>  
>       /* Verify that none of our __u64 fields overflow */
> @@ -1061,11 +1242,11 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>  
>       mutex_lock(&iommu->lock);
>  
> -     mask = ((uint64_t)1 << __ffs(iommu->pgsize_bitmap)) - 1;
> +     pgsize = (size_t)1 << __ffs(iommu->pgsize_bitmap);
>  
> -     WARN_ON(mask & PAGE_MASK);
> +     WARN_ON((pgsize - 1) & PAGE_MASK);
>  
> -     if (!prot || !size || (size | iova | vaddr) & mask) {
> +     if (!prot || !size || (size | iova | vaddr) & (pgsize - 1)) {
>               ret = -EINVAL;
>               goto out_unlock;
>       }
> @@ -1142,6 +1323,12 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>       else
>               ret = vfio_pin_map_dma(iommu, dma, size);
>  
> +     if (!ret && iommu->dirty_page_tracking) {
> +             ret = vfio_dma_bitmap_alloc(dma, pgsize);
> +             if (ret)
> +                     vfio_remove_dma(iommu, dma);
> +     }
> +
>  out_unlock:
>       mutex_unlock(&iommu->lock);
>       return ret;
> @@ -2288,6 +2475,104 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>  
>               return copy_to_user((void __user *)arg, &unmap, minsz) ?
>                       -EFAULT : 0;
> +     } else if (cmd == VFIO_IOMMU_DIRTY_PAGES) {
> +             struct vfio_iommu_type1_dirty_bitmap dirty;
> +             uint32_t mask = VFIO_IOMMU_DIRTY_PAGES_FLAG_START |
> +                             VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP |
> +                             VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP;
> +             int ret = 0;
> +
> +             if (!iommu->v2)
> +                     return -EACCES;
> +
> +             minsz = offsetofend(struct vfio_iommu_type1_dirty_bitmap,
> +                                 flags);
> +
> +             if (copy_from_user(&dirty, (void __user *)arg, minsz))
> +                     return -EFAULT;
> +
> +             if (dirty.argsz < minsz || dirty.flags & ~mask)
> +                     return -EINVAL;
> +
> +             /* only one flag should be set at a time */
> +             if (__ffs(dirty.flags) != __fls(dirty.flags))
> +                     return -EINVAL;
> +
> +             if (dirty.flags & VFIO_IOMMU_DIRTY_PAGES_FLAG_START) {
> +                     size_t pgsize;
> +
> +                     mutex_lock(&iommu->lock);
> +                     pgsize = 1 << __ffs(iommu->pgsize_bitmap);
> +                     if (!iommu->dirty_page_tracking) {
> +                             ret = vfio_dma_bitmap_alloc_all(iommu, pgsize);
> +                             if (!ret)
> +                                     iommu->dirty_page_tracking = true;
> +                     }
> +                     mutex_unlock(&iommu->lock);
> +                     return ret;
> +             } else if (dirty.flags & VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP) {
> +                     mutex_lock(&iommu->lock);
> +                     if (iommu->dirty_page_tracking) {
> +                             iommu->dirty_page_tracking = false;
> +                             vfio_dma_bitmap_free_all(iommu);
> +                     }
> +                     mutex_unlock(&iommu->lock);
> +                     return 0;
> +             } else if (dirty.flags &
> +                              VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP) {
> +                     struct vfio_iommu_type1_dirty_bitmap_get range;
> +                     unsigned long pgshift;
> +                     size_t data_size = dirty.argsz - minsz;
> +                     size_t iommu_pgsize;
> +
> +                     if (!data_size || data_size < sizeof(range))
> +                             return -EINVAL;
> +
> +                     if (copy_from_user(&range, (void __user *)(arg + minsz),
> +                                        sizeof(range)))
> +                             return -EFAULT;
> +
> +                     if (range.iova + range.size < range.iova)
> +                             return -EINVAL;
> +                     if (!access_ok((void __user *)range.bitmap.data,
> +                                    range.bitmap.size))
> +                             return -EINVAL;
> +
> +                     pgshift = __ffs(range.bitmap.pgsize);
> +                     ret = verify_bitmap_size(range.size >> pgshift,
> +                                              range.bitmap.size);
> +                     if (ret)
> +                             return ret;
> +
> +                     mutex_lock(&iommu->lock);
> +
> +                     iommu_pgsize = (size_t)1 << __ffs(iommu->pgsize_bitmap);
> +
> +                     /* allow only smallest supported pgsize */
> +                     if (range.bitmap.pgsize != iommu_pgsize) {
> +                             ret = -EINVAL;
> +                             goto out_unlock;
> +                     }
> +                     if (range.iova & (iommu_pgsize - 1)) {
> +                             ret = -EINVAL;
> +                             goto out_unlock;
> +                     }
> +                     if (!range.size || range.size & (iommu_pgsize - 1)) {
> +                             ret = -EINVAL;
> +                             goto out_unlock;
> +                     }
> +
> +                     if (iommu->dirty_page_tracking)
> +                             ret = vfio_iova_dirty_bitmap(range.bitmap.data,
> +                                             iommu, range.iova, range.size,
> +                                             range.bitmap.pgsize);
> +                     else
> +                             ret = -EINVAL;
> +out_unlock:
> +                     mutex_unlock(&iommu->lock);
> +
> +                     return ret;
> +             }
>       }
>  
>       return -ENOTTY;
> @@ -2355,10 +2640,19 @@ static int vfio_iommu_type1_dma_rw_chunk(struct 
> vfio_iommu *iommu,
>  
>       vaddr = dma->vaddr + offset;
>  
> -     if (write)
> +     if (write) {
>               *copied = copy_to_user((void __user *)vaddr, data,
>                                        count) ? 0 : count;
> -     else
> +             if (*copied && iommu->dirty_page_tracking) {
> +                     unsigned long pgshift = __ffs(iommu->pgsize_bitmap);
> +                     /*
> +                      * Bitmap populated with the smallest supported page
> +                      * size
> +                      */
> +                     bitmap_set(dma->bitmap, offset >> pgshift,
> +                                *copied >> pgshift);
> +             }
> +     } else
>               *copied = copy_from_user(data, (void __user *)vaddr,
>                                          count) ? 0 : count;
>       if (kthread)