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

[Kirti Wankhede <kwankhede@xxxxxxxxxx>]

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 <kwankhede@xxxxxxxxxx>
> > Reviewed-by: Neo Jia <cjia@xxxxxxxxxx>
> > ---
> >   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 (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.

> 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.

> > +	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.

Thanks,
Kirti


> > +	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