Re: [PATCH v13 Kernel 4/7] vfio iommu: Implementation of ioctl to for dirty pages tracking.

[Dr. David Alan Gilbert]

* Kirti Wankhede (address@hidden) wrote:
> VFIO_IOMMU_DIRTY_PAGES ioctl performs three operations:
> - Start pinned and unpinned pages tracking while migration is active
> - Stop pinned and unpinned dirty pages tracking. This is also used to
>   stop dirty pages tracking if migration failed or cancelled.
> - Get dirty pages bitmap. This ioctl returns bitmap of dirty pages, its
>   user space application 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 when dirty logging is enabled for those
> vfio_dmas whose vpfn list is not empty or whole range is mapped, in
> case of pass-through device.
> 
> 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 and unpinning functions. 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>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 243 
> +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 237 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index d386461e5d11..435e84269a28 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -70,6 +70,7 @@ struct vfio_iommu {
>       unsigned int            dma_avail;
>       bool                    v2;
>       bool                    nesting;
> +     bool                    dirty_page_tracking;
>  };
>  
>  struct vfio_domain {
> @@ -90,6 +91,7 @@ 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 {
> @@ -125,6 +127,7 @@ struct vfio_regions {
>                                       (!list_empty(&iommu->domain_list))
>  
>  static int put_pfn(unsigned long pfn, int prot);
> +static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu);
>  
>  /*
>   * This code handles mapping and unmapping of user data buffers
> @@ -174,6 +177,76 @@ static void vfio_unlink_dma(struct vfio_iommu *iommu, 
> struct vfio_dma *old)
>       rb_erase(&old->node, &iommu->dma_list);
>  }
>  
> +static inline unsigned long dirty_bitmap_bytes(unsigned int npages)
> +{
> +     if (!npages)
> +             return 0;
> +
> +     return ALIGN(npages, BITS_PER_LONG) / sizeof(unsigned long);
> +}
> +
> +static int vfio_dma_bitmap_alloc(struct vfio_dma *dma, unsigned long pgsize)
> +{
> +     if (!RB_EMPTY_ROOT(&dma->pfn_list) || dma->iommu_mapped) {
> +             unsigned long npages = dma->size / pgsize;
> +
> +             dma->bitmap = kvzalloc(dirty_bitmap_bytes(npages), GFP_KERNEL);
> +             if (!dma->bitmap)
> +                     return -ENOMEM;
> +     }
> +     return 0;
> +}
> +
> +static int vfio_dma_all_bitmap_alloc(struct vfio_iommu *iommu,
> +                                  unsigned long pgsize)
> +{
> +     struct rb_node *n = rb_first(&iommu->dma_list);
> +     int ret;
> +
> +     for (; n; n = rb_next(n)) {
> +             struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
> +             struct rb_node *n;
> +
> +             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);
> +
> +                             kfree(dma->bitmap);
> +                             dma->bitmap = NULL;
> +                     }
> +                     return ret;
> +             }
> +
> +             if (!dma->bitmap)
> +                     continue;
> +
> +             for (n = rb_first(&dma->pfn_list); n; n = rb_next(n)) {
> +                     struct vfio_pfn *vpfn = rb_entry(n, struct vfio_pfn,
> +                                                      node);
> +
> +                     bitmap_set(dma->bitmap,
> +                                (vpfn->iova - dma->iova) / pgsize, 1);
> +             }
> +     }
> +     return 0;
> +}
> +
> +static void vfio_dma_all_bitmap_free(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);
> +
> +             kfree(dma->bitmap);
> +             dma->bitmap = NULL;
> +     }
> +}
> +
>  /*
>   * Helper Functions for host iova-pfn list
>   */
> @@ -254,12 +327,16 @@ static struct vfio_pfn *vfio_iova_get_vfio_pfn(struct 
> vfio_dma *dma,
>       return vpfn;
>  }
>  
> -static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn 
> *vpfn)
> +static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn 
> *vpfn,
> +                               bool do_tracking, unsigned long pgsize)
>  {
>       int ret = 0;
>  
>       vpfn->ref_count--;
>       if (!vpfn->ref_count) {
> +             if (do_tracking && dma->bitmap)
> +                     bitmap_set(dma->bitmap,
> +                                (vpfn->iova - dma->iova) / pgsize, 1);
>               ret = put_pfn(vpfn->pfn, dma->prot);
>               vfio_remove_from_pfn_list(dma, vpfn);
>       }
> @@ -484,7 +561,8 @@ static int vfio_pin_page_external(struct vfio_dma *dma, 
> unsigned long vaddr,
>  }
>  
>  static int vfio_unpin_page_external(struct vfio_dma *dma, dma_addr_t iova,
> -                                 bool do_accounting)
> +                                 bool do_accounting, bool do_tracking,
> +                                 unsigned long pgsize)
>  {
>       int unlocked;
>       struct vfio_pfn *vpfn = vfio_find_vpfn(dma, iova);
> @@ -492,7 +570,7 @@ static int vfio_unpin_page_external(struct vfio_dma *dma, 
> dma_addr_t iova,
>       if (!vpfn)
>               return 0;
>  
> -     unlocked = vfio_iova_put_vfio_pfn(dma, vpfn);
> +     unlocked = vfio_iova_put_vfio_pfn(dma, vpfn, do_tracking, pgsize);
>  
>       if (do_accounting)
>               vfio_lock_acct(dma, -unlocked, true);
> @@ -563,9 +641,26 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
>  
>               ret = vfio_add_to_pfn_list(dma, iova, phys_pfn[i]);
>               if (ret) {
> -                     vfio_unpin_page_external(dma, iova, do_accounting);
> +                     vfio_unpin_page_external(dma, iova, do_accounting,
> +                                              false, 0);
>                       goto pin_unwind;
>               }
> +
> +             if (iommu->dirty_page_tracking) {
> +                     unsigned long pgshift =
> +                                      __ffs(vfio_pgsize_bitmap(iommu));
> +
> +                     if (!dma->bitmap) {
> +                             ret = vfio_dma_bitmap_alloc(dma, 1 << pgshift);
> +                             if (ret) {
> +                                     vfio_unpin_page_external(dma, iova,
> +                                              do_accounting, false, 0);
> +                                     goto pin_unwind;
> +                             }
> +                     }
> +                     bitmap_set(dma->bitmap,
> +                                (vpfn->iova - dma->iova) >> pgshift, 1);
> +             }
>       }
>  
>       ret = i;
> @@ -578,7 +673,7 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
>  
>               iova = user_pfn[j] << PAGE_SHIFT;
>               dma = vfio_find_dma(iommu, iova, PAGE_SIZE);
> -             vfio_unpin_page_external(dma, iova, do_accounting);
> +             vfio_unpin_page_external(dma, iova, do_accounting, false, 0);
>               phys_pfn[j] = 0;
>       }
>  pin_done:
> @@ -612,7 +707,8 @@ static int vfio_iommu_type1_unpin_pages(void *iommu_data,
>               dma = vfio_find_dma(iommu, iova, PAGE_SIZE);
>               if (!dma)
>                       goto unpin_exit;
> -             vfio_unpin_page_external(dma, iova, do_accounting);
> +             vfio_unpin_page_external(dma, iova, do_accounting,
> +                                      iommu->dirty_page_tracking, PAGE_SIZE);
>       }
>  
>  unpin_exit:
> @@ -800,6 +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);
> +     kfree(dma->bitmap);
>       kfree(dma);
>       iommu->dma_avail++;
>  }
> @@ -830,6 +927,54 @@ static unsigned long vfio_pgsize_bitmap(struct 
> vfio_iommu *iommu)
>       return bitmap;
>  }
>  
> +static int vfio_iova_dirty_bitmap(struct vfio_iommu *iommu, dma_addr_t iova,
> +                               size_t size, uint64_t pgsize,
> +                               unsigned char __user *bitmap)
> +{
> +     struct vfio_dma *dma;
> +     unsigned long pgshift = __ffs(pgsize);
> +     unsigned int npages, bitmap_size;
> +
> +     dma = vfio_find_dma(iommu, iova, 1);
> +
> +     if (!dma)
> +             return -EINVAL;
> +
> +     if (dma->iova != iova || dma->size != size)
> +             return -EINVAL;
> +
> +     npages = dma->size >> pgshift;
> +     bitmap_size = dirty_bitmap_bytes(npages);
> +
> +     /* mark all pages dirty if all pages are pinned and mapped. */
> +     if (dma->iommu_mapped)
> +             bitmap_set(dma->bitmap, 0, npages);
> +
> +     if (dma->bitmap) {
> +             if (copy_to_user((void __user *)bitmap, dma->bitmap,
> +                              bitmap_size))
> +                     return -EFAULT;
> +
> +             memset(dma->bitmap, 0, bitmap_size);
> +     }
> +     return 0;
> +}
> +
> +static int verify_bitmap_size(unsigned long npages, unsigned long 
> bitmap_size)
> +{
> +     long bsize;
> +
> +     if (!bitmap_size || bitmap_size > SIZE_MAX)
> +             return -EINVAL;
> +
> +     bsize = dirty_bitmap_bytes(npages);
> +
> +     if (bitmap_size < bsize)
> +             return -EINVAL;
> +
> +     return 0;
> +}
> +
>  static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>                            struct vfio_iommu_type1_dma_unmap *unmap)
>  {
> @@ -2277,6 +2422,92 @@ 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;
> +
> +             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;

It seems a bit odd to use a set of ORable flags when only one can be set
at a time.

> +             if (dirty.flags & VFIO_IOMMU_DIRTY_PAGES_FLAG_START) {
> +                     unsigned long iommu_pgsize =
> +                                     1 << __ffs(vfio_pgsize_bitmap(iommu));
> +
> +                     mutex_lock(&iommu->lock);
> +                     ret = vfio_dma_all_bitmap_alloc(iommu, 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_all_bitmap_free(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;
> +                     uint64_t iommu_pgsize =
> +                                      1 << __ffs(vfio_pgsize_bitmap(iommu));
> +
> +                     if (!data_size || data_size < sizeof(range))
> +                             return -EINVAL;
> +
> +                     if (copy_from_user(&range, (void __user *)(arg + minsz),
> +                                        sizeof(range)))
> +                             return -EFAULT;
> +
> +                     // allow only min supported pgsize
> +                     if (range.pgsize != iommu_pgsize)
> +                             return -EINVAL;
> +                     if (range.iova & (iommu_pgsize - 1))
> +                             return -EINVAL;
> +                     if (!range.size || range.size & (iommu_pgsize - 1))
> +                             return -EINVAL;
> +                     if (range.iova + range.size < range.iova)
> +                             return -EINVAL;
> +                     if (!access_ok((void __user *)range.bitmap,
> +                                    range.bitmap_size))
> +                             return -EINVAL;
> +
> +                     pgshift = __ffs(range.pgsize);
> +                     ret = verify_bitmap_size(range.size >> pgshift,
> +                                              range.bitmap_size);
> +                     if (ret)
> +                             return ret;
> +
> +                     mutex_lock(&iommu->lock);
> +                     if (iommu->dirty_page_tracking)
> +                             ret = vfio_iova_dirty_bitmap(iommu, range.iova,
> +                                      range.size, range.pgsize,
> +                                      (unsigned char __user *)range.bitmap);
> +                     else
> +                             ret = -EINVAL;
> +                     mutex_unlock(&iommu->lock);
> +
> +                     return ret;
> +             }
>       }
>  
>       return -ENOTTY;
> -- 
> 2.7.0
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK