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

[Kirti Wankhede <kwankhede@nvidia.com>]

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@nvidia.com>
>> Reviewed-by: Neo Jia <cjia@nvidia.com>
>> ---
>>   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
>>