Re: [PATCH v16 Kernel 4/7] vfio iommu: Implementation of ioctl for dirty pages tracking.

[Yan Zhao]

On Fri, Mar 27, 2020 at 01:28:13PM +0800, Kirti Wankhede wrote:
> Hit send button little early.
> 
>  >
>  > I checked v12, it's not like what I said.
>  > In v12, bitmaps are generated per vfio_dma, and combination of the
>  > bitmaps are required in order to generate a big bitmap suiting for dirty
>  > query. It can cause problem when offset not aligning.
>  > But what I propose here is to generate an rb tree orthogonal to the tree
>  > of vfio_dma.
>  >
>  > as to CPU cycles saving, I don't think iterating/translating page by page
>  > would achieve that purpose.
>  >
> 
> Instead of creating one extra rb tree for dirty pages tracking in v10 
> tried to use dma->pfn_list itself, we tried changes in v10, v11 and v12, 
> latest version is evolved version with best possible approach after 
> discussion. Probably, go through v11 as well.
> https://patchwork.kernel.org/patch/11298335/
>
I'm not sure why all those previous implementations are bound to
vfio_dma. for vIOMMU on, in most cases, a vfio_dma is only for a page,
so generating a one-byte bitmap for a single page in each vfio_dma ?
is it possible to creating one extra rb tree to keep dirty ranges, and
one fixed length kernel bitmap whose content is generated on query,
serving as a bouncing buffer for copy_to_user

> 
> On 3/27/2020 6:00 AM, Yan Zhao wrote:
> > On Fri, Mar 27, 2020 at 05:39:01AM +0800, Kirti Wankhede wrote:
> >>
> >>
> >> On 3/25/2020 7:41 AM, Yan Zhao wrote:
> >>> On Wed, Mar 25, 2020 at 05:18:52AM +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 | 266 
> >>>> +++++++++++++++++++++++++++++++++++++++-
> >>>>    1 file changed, 260 insertions(+), 6 deletions(-)
> >>>>
> >>>> diff --git a/drivers/vfio/vfio_iommu_type1.c 
> >>>> b/drivers/vfio/vfio_iommu_type1.c
> >>>> index 70aeab921d0f..874a1a7ae925 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  (uint64_t)(INT_MAX - 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 +191,77 @@ 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;
> >>>> +
If pgsize > dma->size, npages = 0.
wouldn't it cause problem?


> >>>> +        if (npages > DIRTY_BITMAP_PAGES_MAX)
> >>>> +                return -EINVAL;
> >>>> +
> >>>> +        dma->bitmap = kvzalloc(DIRTY_BITMAP_BYTES(npages), GFP_KERNEL);
> >>>> +        if (!dma->bitmap)
> >>>> +                return -ENOMEM;
> >>>> +
> >>>> +        return 0;
> >>>> +}
> >>>> +
> >>>> +static void vfio_dma_bitmap_free(struct vfio_dma *dma)
> >>>> +{
> >>>> +        kfree(dma->bitmap);
> >>>> +        dma->bitmap = NULL;
> >>>> +}
> >>>> +
> >>>> +static void vfio_dma_populate_bitmap(struct vfio_dma *dma, uint64_t 
> >>>> pgsize)
> >>>> +{
> >>>> +        struct rb_node *p;
> >>>> +
> >>>> +        if (RB_EMPTY_ROOT(&dma->pfn_list))
> >>>> +                return;
> >>>> +
> >>>> +        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);
> >>>> +        }
> >>>> +}
> >>>> +
> >>>> +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);
> >>>> +                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);
> >>>> +
> >>>> +                                vfio_dma_bitmap_free(dma);
> >>>> +                        }
> >>>> +                        return ret;
> >>>> +                }
> >>>> +                vfio_dma_populate_bitmap(dma, pgsize);
> >>>> +        }
> >>>> +        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);
> >>>> +
> >>>> +                vfio_dma_bitmap_free(dma);
> >>>> +        }
> >>>> +}
> >>>> +
> >>>>    /*
> >>>>     * Helper Functions for host iova-pfn list
> >>>>     */
> >>>> @@ -567,6 +654,18 @@ 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 populated with the smallest supported 
> >>>> page
> >>>> +                         * size
> >>>> +                         */
> >>>> +                        bitmap_set(dma->bitmap,
> >>>> +                                   (vpfn->iova - dma->iova) >> pgshift, 
> >>>> 1);
> >>>> +                }
> >>>>          }
> >>>>    
> >>>>          ret = i;
> >>>> @@ -801,6 +900,7 @@ 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);
> >>>> +        vfio_dma_bitmap_free(dma);
> >>>>          kfree(dma);
> >>>>          iommu->dma_avail++;
> >>>>    }
> >>>> @@ -831,6 +931,57 @@ 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;
> >>>> +
> >>> Still don't sure if it's a good practice.
> >>> I saw the qemu implementation.
> >>> Qemu just iterates the whole IOVA address space,
> >>> It needs to find IOTLB entry for an IOVA
> >>> (1) if it can find an IOTLB for an IOVA, do the DIRTY_PAGES IOCTL and
> >>> increment IOVA by (iotlb.addr_mask + 1)
> >>>
> >>> (2) if no existing IOTLB found, the imrc->translate needs to go searching 
> >>> shadow
> >>> page table to try to generate one.
> >>> if it still fails,(most probably case, as IOMMU only maps a small part in 
> >>> its address
> >>> space).  increment IOVA by 1 page.
> >>>
> >>> So, if the address space width is 39bit, and if there's only one page
> >>> mapped, you still have to translate IOVA for around 2^27 times in each
> >>> query. Isn't it too inefficient?
> >>>
> >>
> >> This is Qemu side implementation, let discuss it on QEMU patches.
> >>
> > But kernel has to support it first, right?
> > 
> >>> So, IMHO, why we could not just save an rb tree specific for dirty pages, 
> >>> then generate
> >>> a bitmap for each query?
> >>
> >> This is looping back to implentation in v10 - v12 version. There are
> >> problems discussed during v10 to v12 version of patches with this approach.
> >> - populating dirty bitmap at the time of query will add more CPU cycles.
> >> - If we save these CPU cyles means dirty pages need to be tracked when
> >> they are pinned or dirtied by CPU, that is, inttoduced per vfio_dma
> >> bitmap. If ranges are not vfio_dma aligned, then copying bitmap to user
> >> space becomes complicated and unefficient.
> >>
> >> So we decided to go with the approach implemented here.
> > 
> > I checked v12, it's not like what I said.
> > In v12, bitmaps are generated per vfio_dma, and combination of the
> > bitmaps are required in order to generate a big bitmap suiting for dirty
> > query. It can cause problem when offset not aligning.
> > But what I propose here is to generate an rb tree orthogonal to the tree
> > of vfio_dma.
> > 
> > as to CPU cycles saving, I don't think iterating/translating page by page
> > would achieve that purpose.
> > 
> > 
> > 
> >>>
> >>>> +        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;
> >>>> +
> >>>> +        /*
> >>>> +         * Re-populate bitmap to include all pinned pages which are 
> >>>> considered
> >>>> +         * as dirty but exclude pages which are unpinned and pages 
> >>>> which are
> >>>> +         * marked dirty by vfio_dma_rw()
> >>>> +         */
> >>>> +        bitmap_clear(dma->bitmap, 0, npages);
> >>>> +        vfio_dma_populate_bitmap(dma, pgsize);
> >>> will this also repopulate bitmap for pinned pages set by pass-through 
> >>> devices in
> >>> patch 07 ?
> >>>
> >>
> >> If pass through device's driver pins pages using vfio_pin_pages and all
> >> devices in the group pins pages through vfio_pin_pages, then
> >> iommu->pinned_page_dirty_scope is set true, then bitmap is repolutated.
> >>
> >>
> > pass-through devices already have all guest memory pinned, it would have
> > no reason to call vfio_pin_pages if not attempting to mark page dirty.
> > Then if it calls vfio_pin_pages, it means "the pages are accessed, please
> > mark them dirty, feel free to clean it when you get it",
> > not "the pages will be accesses, please mark them dirty continuously"
> > 
> > Thanks
> > Yan
> > 
> >>
> >>>
> >>>> +        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 +1189,16 @@ 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 +1206,7 @@ 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 +1281,12 @@ 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 +2435,93 @@ 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 smallest 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 +2589,20 @@ 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 populated with the smallest supported 
> >>>> page
> >>>> +                         * size
> >>>> +                         */
> >>>> +                        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
> >>>>