Re: [PATCH v12 Kernel 4/7] vfio iommu: Implementation of ioctl to for dirty pages tracking.

Yan Zhao
2020-02-10T09:59:17Z

On Sat, Feb 08, 2020 at 03:42:31AM +0800, Kirti Wankhede 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.
>
> There could be multiple option as to when bitmap should be populated:
> * Polulate bitmap for already pinned pages when bitmap is allocated for
> a vfio_dma with the smallest supported page size. Updates bitmap from
> page 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,
> re-populated bitmap according to requested page size and then copy to
> user.
> Pros: Bitmap gets populated on the fly after dirty tracking has
> started.
> Cons: If requested page size is different than smallest supported
> page size, then bitmap has to be re-populated again, with
> additional overhead of allocating bitmap memory again for
> re-population of bitmap.
>
> * Populate bitmap when bitmap is queried by user application.
> Pros: Bitmap is populated with requested page size. This eliminates
> the need to re-populate bitmap if requested page size is
> different than smallest supported pages size.
> Cons: There is one time processing time, when bitmap is queried.
>
> I prefer later option with simple logic and to eliminate over-head of
> bitmap repopulation in case of differnt page sizes. Later option is
> implemented in this patch.
>
> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> Reviewed-by: Neo Jia <cjia@nvidia.com>
> ---
> drivers/vfio/vfio_iommu_type1.c | 299 ++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 287 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index d386461e5d11..df358dc1c85b 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 +177,57 @@ 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_iommu *iommu,
> + struct vfio_dma *dma, unsigned long pgsizes)
> +{
> + unsigned long pgshift = __ffs(pgsizes);
> +
> + if (!RB_EMPTY_ROOT(&dma->pfn_list) || dma->iommu_mapped) {
> + unsigned long npages = dma->size >> pgshift;
> + unsigned long bsize = dirty_bitmap_bytes(npages);
> +
> + dma->bitmap = kvzalloc(bsize, GFP_KERNEL);
> + if (!dma->bitmap)
> + return -ENOMEM;
> + }
> + return 0;
> +}
> +
> +static int vfio_dma_all_bitmap_alloc(struct vfio_iommu *iommu,
> + unsigned long pgsizes)
> +{
> + 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);
> +
> + ret = vfio_dma_bitmap_alloc(iommu, dma, pgsizes);
> + if (ret)
> + return ret;
> + }
> + 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);
> + }
> +}
> +
> /*
> * Helper Functions for host iova-pfn list
> */
> @@ -244,6 +298,29 @@ static void vfio_remove_from_pfn_list(struct vfio_dma *dma,
> kfree(vpfn);
> }
>
> +static void vfio_remove_unpinned_from_pfn_list(struct vfio_dma *dma)
> +{
> + struct rb_node *n = rb_first(&dma->pfn_list);
> +
> + for (; n; n = rb_next(n)) {
> + struct vfio_pfn *vpfn = rb_entry(n, struct vfio_pfn, node);
> +
> + if (!vpfn->ref_count)
> + vfio_remove_from_pfn_list(dma, vpfn);
> + }
> +}
> +
> +static void vfio_remove_unpinned_from_dma_list(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_remove_unpinned_from_pfn_list(dma);
> + }
> +}
> +
> static struct vfio_pfn *vfio_iova_get_vfio_pfn(struct vfio_dma *dma,
> unsigned long iova)
> {
> @@ -261,7 +338,8 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn *vpfn)
> vpfn->ref_count--;
> if (!vpfn->ref_count) {
> ret = put_pfn(vpfn->pfn, dma->prot);
> - vfio_remove_from_pfn_list(dma, vpfn);
> + if (!dma->bitmap)
> + vfio_remove_from_pfn_list(dma, vpfn);
> }
> return ret;
> }
> @@ -483,13 +561,14 @@ static int vfio_pin_page_external(struct vfio_dma *dma, unsigned long vaddr,
> return ret;
> }
>
> -static int vfio_unpin_page_external(struct vfio_dma *dma, dma_addr_t iova,
> +static int vfio_unpin_page_external(struct vfio_iommu *iommu,
> + struct vfio_dma *dma, dma_addr_t iova,
> bool do_accounting)
> {
> int unlocked;
> struct vfio_pfn *vpfn = vfio_find_vpfn(dma, iova);
>
> - if (!vpfn)
> + if (!vpfn || !vpfn->ref_count)
> return 0;
>
> unlocked = vfio_iova_put_vfio_pfn(dma, vpfn);
> @@ -510,6 +589,7 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
> unsigned long remote_vaddr;
> struct vfio_dma *dma;
> bool do_accounting;
> + unsigned long iommu_pgsizes = vfio_pgsize_bitmap(iommu);
>
> if (!iommu || !user_pfn || !phys_pfn)
> return -EINVAL;
> @@ -551,8 +631,10 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
>
> vpfn = vfio_iova_get_vfio_pfn(dma, iova);
> if (vpfn) {
> - phys_pfn[i] = vpfn->pfn;
> - continue;
> + if (vpfn->ref_count > 1) {
> + phys_pfn[i] = vpfn->pfn;
> + continue;
> + }
> }
>
> remote_vaddr = dma->vaddr + iova - dma->iova;
> @@ -560,11 +642,23 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
> do_accounting);
> if (ret)
> goto pin_unwind;
> -
> - ret = vfio_add_to_pfn_list(dma, iova, phys_pfn[i]);
> - if (ret) {
> - vfio_unpin_page_external(dma, iova, do_accounting);
> - goto pin_unwind;
> + if (!vpfn) {
> + ret = vfio_add_to_pfn_list(dma, iova, phys_pfn[i]);
> + if (ret) {
> + vfio_unpin_page_external(iommu, dma, iova,
> + do_accounting);
> + goto pin_unwind;
> + }
> + } else
> + vpfn->pfn = phys_pfn[i];
> +
> + if (iommu->dirty_page_tracking && !dma->bitmap) {
> + ret = vfio_dma_bitmap_alloc(iommu, dma, iommu_pgsizes);
> + if (ret) {
> + vfio_unpin_page_external(iommu, dma, iova,
> + do_accounting);
> + goto pin_unwind;
> + }
> }
> }
>
> @@ -578,7 +672,7 @@ 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(iommu, dma, iova, do_accounting);
> phys_pfn[j] = 0;
> }
> pin_done:
> @@ -612,7 +706,7 @@ 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(iommu, dma, iova, do_accounting);
> }
>
> unpin_exit:
> @@ -830,6 +924,113 @@ 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;
> + dma_addr_t i = iova, iova_limit;
> + unsigned int bsize, nbits = 0, l = 0;
> + unsigned long pgshift = __ffs(pgsize);
> +
> + while ((dma = vfio_find_dma(iommu, i, pgsize))) {
> + int ret, j;
> + unsigned int npages = 0, shift = 0;
> + unsigned char temp = 0;
> +
> + /* mark all pages dirty if all pages are pinned and mapped. */
> + if (dma->iommu_mapped) {
> + iova_limit = min(dma->iova + dma->size, iova + size);
> + npages = iova_limit/pgsize;
> + bitmap_set(dma->bitmap, 0, npages);
for pass-through devices, it's not good to always return all pinned pages as
dirty. could it also call vfio_pin_pages to track dirty pages? or any
other interface provided to do that?
> + } else if (dma->bitmap) {
> + struct rb_node *n = rb_first(&dma->pfn_list);
> + bool found = false;
> +
> + for (; n; n = rb_next(n)) {
> + struct vfio_pfn *vpfn = rb_entry(n,
> + struct vfio_pfn, node);
> + if (vpfn->iova >= i) {
> + found = true;
> + break;
> + }
> + }
> +
> + if (!found) {
> + i += dma->size;
> + continue;
> + }
> +
> + for (; n; n = rb_next(n)) {
> + unsigned int s;
> + struct vfio_pfn *vpfn = rb_entry(n,
> + struct vfio_pfn, node);
> +
> + if (vpfn->iova >= iova + size)
> + break;
> +
> + s = (vpfn->iova - dma->iova) >> pgshift;
> + bitmap_set(dma->bitmap, s, 1);
> +
should not set the dma->bitmap when user space asks for dirty bitmap.
should set the bits for all vpfns when dirty page tracking starts, and clear
it after putting them to user space.
dma->bitmap is set when vfio_pin_pages is called during dirty page
tracking.
> + iova_limit = vpfn->iova + pgsize;
> + }
> + npages = iova_limit/pgsize;
> + }
> +
> + bsize = dirty_bitmap_bytes(npages);
> + shift = nbits % BITS_PER_BYTE;
> +
> + if (npages && shift) {
> + l--;
> + if (!access_ok((void __user *)bitmap + l,
> + sizeof(unsigned char)))
> + return -EINVAL;
> +
> + ret = __get_user(temp, bitmap + l);
> + if (ret)
> + return ret;
> + }
> +
> + for (j = 0; j < bsize; j++, l++) {
> + temp = temp |
> + (*((unsigned char *)dma->bitmap + j) << shift);
> + if (!access_ok((void __user *)bitmap + l,
> + sizeof(unsigned char)))
> + return -EINVAL;
> +
> + ret = __put_user(temp, bitmap + l);
> + if (ret)
> + return ret;
> + if (shift) {
> + temp = *((unsigned char *)dma->bitmap + j) >>
> + (BITS_PER_BYTE - shift);
> + }
> + }
> +
> + nbits += npages;
> +
> + i = min(dma->iova + dma->size, iova + size);
> + if (i >= iova + size)
> + break;
> + }
> + return 0;
> +}
> +
> +static long 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 bsize;
> +}
> +
> static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
> struct vfio_iommu_type1_dma_unmap *unmap)
> {
> @@ -2277,6 +2478,80 @@ 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 range;
> + 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,
> + bitmap);
> +
> + if (copy_from_user(&range, (void __user *)arg, minsz))
> + return -EFAULT;
> +
> + if (range.argsz < minsz || range.flags & ~mask)
> + return -EINVAL;
> +
> + /* only one flag should be set at a time */
> + if (__ffs(range.flags) != __fls(range.flags))
> + return -EINVAL;
> +
> + if (range.flags & VFIO_IOMMU_DIRTY_PAGES_FLAG_START) {
> + unsigned long iommu_pgsizes = vfio_pgsize_bitmap(iommu);
> +
> + mutex_lock(&iommu->lock);
> + iommu->dirty_page_tracking = true;
should only set iommu->dirty_page_tracking = true after bitmap alloc
succeeds.
> + ret = vfio_dma_all_bitmap_alloc(iommu, iommu_pgsizes);
> + mutex_unlock(&iommu->lock);
> + return ret;
> + } else if (range.flags & VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP) {
> + mutex_lock(&iommu->lock);
> + iommu->dirty_page_tracking = false;
> + vfio_dma_all_bitmap_free(iommu);
> + vfio_remove_unpinned_from_dma_list(iommu);
> + mutex_unlock(&iommu->lock);
> + return 0;
> + } else if (range.flags &
> + VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP) {
> + long bsize;
> + unsigned long pgshift = __ffs(range.pgsize);
> + uint64_t iommu_pgsizes = vfio_pgsize_bitmap(iommu);
> + uint64_t iommu_pgmask =
> + ((uint64_t)1 << __ffs(iommu_pgsizes)) - 1;
> +
> + if ((range.pgsize & iommu_pgsizes) != range.pgsize)
> + return -EINVAL;
> + if (range.iova & iommu_pgmask)
> + return -EINVAL;
> + if (!range.size || range.size & iommu_pgmask)
> + return -EINVAL;
> + if (range.iova + range.size < range.iova)
> + return -EINVAL;
> + if (!access_ok((void __user *)range.bitmap,
> + range.bitmap_size))
> + return -EINVAL;
> +
> + bsize = verify_bitmap_size(range.size >> pgshift,
> + range.bitmap_size);
> + if (bsize < 0)
> + return bsize;
> +
> + 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
>