Re: [PATCH v15 Kernel 4/7] vfio iommu: Implementation of ioctl for dirty pages tracking.

[Alex Williamson]

On Fri, 20 Mar 2020 23:19:14 +0530
Kirti Wankhede <address@hidden> wrote:

> On 3/20/2020 4:27 AM, Alex Williamson wrote:
> > On Fri, 20 Mar 2020 01:46:41 +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>
> >> ---
> >>   drivers/vfio/vfio_iommu_type1.c | 242 
> >> +++++++++++++++++++++++++++++++++++++++-
> >>   1 file changed, 236 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/vfio/vfio_iommu_type1.c 
> >> b/drivers/vfio/vfio_iommu_type1.c
> >> index 70aeab921d0f..239f61764d03 100644
> >> --- a/drivers/vfio/vfio_iommu_type1.c
> >> +++ b/drivers/vfio/vfio_iommu_type1.c
> >> @@ -71,6 +71,7 @@ struct vfio_iommu {
> >>    unsigned int            dma_avail;
> >>    bool                    v2;
> >>    bool                    nesting;
> >> +  bool                    dirty_page_tracking;
> >>   };
> >>   
> >>   struct vfio_domain {
> >> @@ -91,6 +92,7 @@ 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 {
> >> @@ -125,7 +127,21 @@ 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    ((1UL << 31) - 1)
> >> +#define DIRTY_BITMAP_SIZE_MAX      
> >> DIRTY_BITMAP_BYTES(DIRTY_BITMAP_PAGES_MAX)
> >> +
> >>   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
> >> @@ -175,6 +191,67 @@ 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, uint64_t pgsize)
> >> +{
> >> +  uint64_t npages = dma->size / pgsize;
> >> +  
> > 
> > Shouldn't we test this against one of the MAX macros defined above?  It
> > would be bad if we could enabled dirty tracking but not allow the user
> > to retrieve it.
> >   
> 
> Yes, adding check as below:
> 
>          if (npages > DIRTY_BITMAP_PAGES_MAX)
>                  -EINVAL;
> 
> 
> >> +  dma->bitmap = kvzalloc(DIRTY_BITMAP_BYTES(npages), GFP_KERNEL);
> >> +  if (!dma->bitmap)
> >> +          return -ENOMEM;
> >> +
> >> +  return 0;
> >> +}
> >> +
> >> +static int vfio_dma_bitmap_alloc_all(struct vfio_iommu *iommu, uint64_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);
> >> +          struct rb_node *p;
> >> +          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);
> >> +
> >> +                          kfree(dma->bitmap);
> >> +                          dma->bitmap = NULL;
> >> +                  }
> >> +                  return ret;
> >> +          }
> >> +
> >> +          if (RB_EMPTY_ROOT(&dma->pfn_list))
> >> +                  continue;
> >> +
> >> +          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);
> >> +          }
> >> +  }
> >> +  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);
> >> +
> >> +          kfree(dma->bitmap);
> >> +          dma->bitmap = NULL;  
> > 
> > Might be useful to have a vfio_dma_bitmap_free() for here and above.
> >   
> 
> Ok.
> 
> >> +  }
> >> +}
> >> +
> >>   /*
> >>    * Helper Functions for host iova-pfn list
> >>    */
> >> @@ -567,6 +644,14 @@ 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(vfio_pgsize_bitmap(iommu));
> >> +
> >> +                  bitmap_set(dma->bitmap,
> >> +                             (vpfn->iova - dma->iova) >> pgshift, 1);
> >> +          }
> >>    }
> >>   
> >>    ret = i;
> >> @@ -801,6 +886,7 @@ 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++;
> >>   }
> >> @@ -831,6 +917,50 @@ 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,
> >> +                            u64 __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 (copy_to_user((void __user *)bitmap, dma->bitmap, bitmap_size))
> >> +          return -EFAULT;  
> > 
> > We still need to reset the bitmap here, clearing and re-adding the
> > pages that are still pinned.
> > 
> > https://lore.kernel.org/kvm/address@hidden/
> >   
> 
> I thought you agreed on my reply to it
> https://lore.kernel.org/kvm/address@hidden/
> 
>  > Why re-populate when there will be no change since
>  > vfio_iova_dirty_bitmap() is called holding iommu->lock? If there is any
>  > pin request while vfio_iova_dirty_bitmap() is still working, it will
>  > wait till iommu->lock is released. Bitmap will be populated when page is
>  > pinned.  

As coded, dirty bits are only ever set in the bitmap, never cleared.
If a page is unpinned between iterations of the user recording the
dirty bitmap, it should be marked dirty in the iteration immediately
after the unpinning and not marked dirty in the following iteration.
That doesn't happen here.  We're reporting cumulative dirty pages since
logging was enabled, we need to be reporting dirty pages since the user
last retrieved the dirty bitmap.  The bitmap should be cleared and
currently pinned pages re-added after copying to the user.  Thanks,

Alex

> >> +  return 0;
> >> +}
> >> +
> >> +static int verify_bitmap_size(uint64_t npages, uint64_t bitmap_size)
> >> +{
> >> +  uint64_t bsize;
> >> +
> >> +  if (!npages || !bitmap_size || (bitmap_size > DIRTY_BITMAP_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)
> >>   {
> >> @@ -1038,16 +1168,16 @@ 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;
> >> +  uint64_t pgsize;
> >>    struct vfio_dma *dma;
> >>   
> >>    /* Verify that none of our __u64 fields overflow */
> >>    if (map->size != size || map->vaddr != vaddr || map->iova != iova)
> >>            return -EINVAL;
> >>   
> >> -  mask = ((uint64_t)1 << __ffs(vfio_pgsize_bitmap(iommu))) - 1;
> >> +  pgsize = (uint64_t)1 << __ffs(vfio_pgsize_bitmap(iommu));
> >>   
> >> -  WARN_ON(mask & PAGE_MASK);
> >> +  WARN_ON((pgsize - 1) & PAGE_MASK);
> >>   
> >>    /* READ/WRITE from device perspective */
> >>    if (map->flags & VFIO_DMA_MAP_FLAG_WRITE)
> >> @@ -1055,7 +1185,7 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
> >>    if (map->flags & VFIO_DMA_MAP_FLAG_READ)
> >>            prot |= IOMMU_READ;
> >>   
> >> -  if (!prot || !size || (size | iova | vaddr) & mask)
> >> +  if (!prot || !size || (size | iova | vaddr) & (pgsize - 1))
> >>            return -EINVAL;
> >>   
> >>    /* Don't allow IOVA or virtual address wrap */
> >> @@ -1130,6 +1260,12 @@ 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;
> >> @@ -2278,6 +2414,93 @@ 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) {
> >> +                  uint64_t pgsize = 1 << __ffs(vfio_pgsize_bitmap(iommu));
> >> +
> >> +                  mutex_lock(&iommu->lock);
> >> +                  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;
> >> +                  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.bitmap.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.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);
> >> +                  if (iommu->dirty_page_tracking)
> >> +                          ret = vfio_iova_dirty_bitmap(iommu, range.iova,
> >> +                                          range.size, range.bitmap.pgsize,
> >> +                                          range.bitmap.data);
> >> +                  else
> >> +                          ret = -EINVAL;
> >> +                  mutex_unlock(&iommu->lock);
> >> +
> >> +                  return ret;
> >> +          }
> >>    }
> >>   
> >>    return -ENOTTY;
> >> @@ -2345,10 +2568,17 @@ 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(vfio_pgsize_bitmap(iommu));
> >> +
> >> +                  bitmap_set(dma->bitmap, offset >> pgshift,
> >> +                             *copied >> pgshift);
> >> +          }
> >> +  } else
> >>            *copied = __copy_from_user(data, (void __user *)vaddr,
> >>                                       count) ? 0 : count;
> >>    if (kthread)  
> >   
>