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

From: Kirti Wankhede
Subject: Re: [PATCH v14 Kernel 4/7] vfio iommu: Implementation of ioctl for dirty pages tracking.
Date: Thu, 19 Mar 2020 22:27:30 +0530
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 


On 3/19/2020 6:36 PM, Alex Williamson wrote:

On Thu, 19 Mar 2020 02:15:34 -0400
Yan Zhao <address@hidden> wrote:


On Thu, Mar 19, 2020 at 12:40:53PM +0800, Alex Williamson wrote:

On Thu, 19 Mar 2020 00:15:33 -0400
Yan Zhao <address@hidden> wrote:

On Thu, Mar 19, 2020 at 12:01:00PM +0800, Alex Williamson wrote:

On Wed, 18 Mar 2020 23:06:39 -0400
Yan Zhao <address@hidden> wrote:

On Thu, Mar 19, 2020 at 03:41:11AM +0800, Kirti Wankhede 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 | 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;
  };
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)
+{
+       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;
+

looks this size is passed from user. how can it ensure size always
equals to dma->size ?

shouldn't we iterate dma tree to look for dirty for whole range if a
single dma cannot meet them all?


Please see the discussion on v12[1], the problem is with the alignment
of DMA mapped regions versus the bitmap.  A DMA mapping only requires
page alignment, so for example imagine a user requests the bitmap from
page zero to 4GB, but we have a DMA mapping starting at 4KB.  We can't
efficiently copy the bitmap tracked by the vfio_dma structure to the
user buffer when it's shifted by 1 bit.  Adjacent mappings can also
make for a very complicated implementation.  In the discussion linked
we decided to compromise on a more simple implementation that requires
the user to ask for a bitmap which exactly matches a single DMA
mapping, which Kirti indicates is what we require to support QEMU.
Later in the series, the unmap operation also makes this requirement
when used with the flags to retrieve the dirty bitmap.  Thanks,


so, what about for vIOMMU enabling case?
if IOVAs are mapped per page, then there's a log_sync in qemu,
it's supposed for range from 0-U64MAX, qemu has to find out which
ones are mapped and cut them into pages before calling this IOCTL?
And what if those IOVAs are mapped for len more than one page?


Good question.  Kirti?



In log_sync with vIOMMU, loop for range such that:

- find iotlb entry for iova, get iova_xlat
- size = iotlb.addr_mask + 1; This is same caculation as when mapping are created from vfio_iommu_map_notify() 
- use the <iova_xlat, size> for VFIO_IOMMU_DIRTY_PAGES ioctl
- increment iova: iova += size
- iterate above steps till end of range.


[1] https://lore.kernel.org/kvm/address@hidden/

+       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;
+

Here, dma->bitmap needs to be cleared. right?


Ah, I missed re-checking this in my review.  v13 did clear it, but I
noted that we need to re-populate any currently pinned pages.  This
neither clears nor repopulates.  That's wrong.  Thanks,
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. 

Thanks,
Kirti


Alex

+       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)
+               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)
  {
@@ -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
                *copied = __copy_from_user(data, (void __user *)vaddr,
                                           count) ? 0 : count;
        if (kthread)
--
2.7.0
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