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

[Kirti Wankhede <kwankhede@nvidia.com>]

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/

Thanks,
Kirti

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 <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.
>>
> 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
>>>>