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

Kirti Wankhede
2020-02-07T20:16:48Z

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);
+ } 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);
+
+ 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;
+ 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