Re: [PATCH v14 Kernel 4/7] vfio iommu: Implementation of ioctl for dirty pages tracking.

Alex Williamson
2020-03-19T03:45:12Z

On Thu, 19 Mar 2020 01:11:11 +0530
Kirti Wankhede <kwankhede@nvidia.com> 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 <kwankhede@nvidia.com>
> Reviewed-by: Neo Jia <cjia@nvidia.com>
> ---
> drivers/vfio/vfio_iommu_type1.c | 205 +++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 203 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 70aeab921d0f..d6417fb02174 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;

We've made the bitmap a width invariant u64 else, should be here as
well.

> };
>
> struct vfio_group {
> @@ -125,7 +127,10 @@ 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)
> +
> 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 +180,55 @@ 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_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;
> + unsigned long npages = dma->size / pgsize;
> +
> + dma->bitmap = kvzalloc(DIRTY_BITMAP_BYTES(npages), GFP_KERNEL);
> + if (!dma->bitmap) {
> + 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 -ENOMEM;
> + }
> +
> + 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(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
> */
> @@ -567,6 +621,14 @@ 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 +863,7 @@ 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 +894,50 @@ 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,
> + unsigned char __user *bitmap)

And here, why do callers cast to an unsigned char pointer when we're
going to cast to a void pointer anyway? Should be a u64 __user pointer.

> +{
> + 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;
> +
> + return 0;
> +}
> +
> +static int verify_bitmap_size(uint64_t npages, uint64_t bitmap_size)
> +{
> + uint64_t bsize;
> +
> + if (!npages || !bitmap_size || bitmap_size > UINT_MAX)

As commented previously, how do we derive this UINT_MAX limitation?

> + 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)
> {

We didn't address that vfio_dma_do_map() needs to kvzalloc a bitmap for
any new vfio_dma created while iommu->dirty_page_tracking = true.

> @@ -2278,6 +2385,93 @@ 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(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(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,
> + (unsigned char __user *)range.bitmap.data);
> + else
> + ret = -EINVAL;
> + mutex_unlock(&iommu->lock);
> +
> + return ret;
> + }
> }
>
> return -ENOTTY;
> @@ -2345,10 +2539,17 @@ 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

Great, thanks for adding this!

> *copied = __copy_from_user(data, (void __user *)vaddr,
> count) ? 0 : count;
> if (kthread)