Re: [PATCH Kernel v20 6/8] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap

[Kirti Wankhede <kwankhede@nvidia.com>]

On 5/15/2020 8:57 AM, Alex Williamson wrote:
> On Fri, 15 May 2020 02:07:45 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
> 
>> DMA mapped pages, including those pinned by mdev vendor drivers, might
>> get unpinned and unmapped while migration is active and device is still
>> running. For example, in pre-copy phase while guest driver could access
>> those pages, host device or vendor driver can dirty these mapped pages.
>> Such pages should be marked dirty so as to maintain memory consistency
>> for a user making use of dirty page tracking.
>>
>> To get bitmap during unmap, user should allocate memory for bitmap, set
>> it all zeros, set size of allocated memory, set page size to be
>> considered for bitmap and set flag VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP.
>>
>> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
>> Reviewed-by: Neo Jia <cjia@nvidia.com>
>> ---
>>   drivers/vfio/vfio_iommu_type1.c | 77 ++++++++++++++++++++++++++++++++++-------
>>   include/uapi/linux/vfio.h       | 10 ++++++
>>   2 files changed, 75 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index b76d3b14abfd..a1dc57bcece5 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -195,11 +195,15 @@ static void vfio_unlink_dma(struct vfio_iommu *iommu, struct vfio_dma *old)
>>   static int vfio_dma_bitmap_alloc(struct vfio_dma *dma, size_t pgsize)
>>   {
>>   	uint64_t npages = dma->size / pgsize;
>> +	size_t bitmap_size;
>>   
>>   	if (npages > DIRTY_BITMAP_PAGES_MAX)
>>   		return -EINVAL;
>>   
>> -	dma->bitmap = kvzalloc(DIRTY_BITMAP_BYTES(npages), GFP_KERNEL);
>> +	/* Allocate extra 64 bits which are used for bitmap manipulation */
>> +	bitmap_size = DIRTY_BITMAP_BYTES(npages) + sizeof(u64);
>> +
>> +	dma->bitmap = kvzalloc(bitmap_size, GFP_KERNEL);
>>   	if (!dma->bitmap)
>>   		return -ENOMEM;
>>   
>> @@ -999,23 +1003,25 @@ static int verify_bitmap_size(uint64_t npages, uint64_t bitmap_size)
>>   }
>>   
>>   static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>> -			     struct vfio_iommu_type1_dma_unmap *unmap)
>> +			     struct vfio_iommu_type1_dma_unmap *unmap,
>> +			     struct vfio_bitmap *bitmap)
>>   {
>> -	uint64_t mask;
>>   	struct vfio_dma *dma, *dma_last = NULL;
>> -	size_t unmapped = 0;
>> +	size_t unmapped = 0, pgsize;
>>   	int ret = 0, retries = 0;
>> +	unsigned long pgshift;
>>   
>>   	mutex_lock(&iommu->lock);
>>   
>> -	mask = ((uint64_t)1 << __ffs(iommu->pgsize_bitmap)) - 1;
>> +	pgshift = __ffs(iommu->pgsize_bitmap);
>> +	pgsize = (size_t)1 << pgshift;
>>   
>> -	if (unmap->iova & mask) {
>> +	if (unmap->iova & (pgsize - 1)) {
>>   		ret = -EINVAL;
>>   		goto unlock;
>>   	}
>>   
>> -	if (!unmap->size || unmap->size & mask) {
>> +	if (!unmap->size || unmap->size & (pgsize - 1)) {
>>   		ret = -EINVAL;
>>   		goto unlock;
>>   	}
>> @@ -1026,9 +1032,15 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>   		goto unlock;
>>   	}
>>   
>> -	WARN_ON(mask & PAGE_MASK);
>> -again:
>> +	/* When dirty tracking is enabled, allow only min supported pgsize */
>> +	if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
>> +	    (!iommu->dirty_page_tracking || (bitmap->pgsize != pgsize))) {
>> +		ret = -EINVAL;
>> +		goto unlock;
>> +	}
>>   
>> +	WARN_ON((pgsize - 1) & PAGE_MASK);
>> +again:
>>   	/*
>>   	 * vfio-iommu-type1 (v1) - User mappings were coalesced together to
>>   	 * avoid tracking individual mappings.  This means that the granularity
>> @@ -1066,6 +1078,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>   			ret = -EINVAL;
>>   			goto unlock;
>>   		}
>> +
>>   		dma = vfio_find_dma(iommu, unmap->iova + unmap->size - 1, 0);
>>   		if (dma && dma->iova + dma->size != unmap->iova + unmap->size) {
>>   			ret = -EINVAL;
>> @@ -1083,6 +1096,23 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>   		if (dma->task->mm != current->mm)
>>   			break;
>>   
>> +		if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
>> +		    (dma_last != dma)) {
>> +
>> +			/*
>> +			 * mark all pages dirty if all pages are pinned and
>> +			 * mapped
>> +			 */
>> +			if (dma->iommu_mapped)
>> +				bitmap_set(dma->bitmap, 0,
>> +					   dma->size >> pgshift);
> 
> Nit, all the callers of update_user_bitmap() precede the call with this
> identical operation, we should probably push it into the function to do
> it.
> 
>> +
>> +			ret = update_user_bitmap(bitmap->data, dma,
>> +						 unmap->iova, pgsize);
>> +			if (ret)
>> +				break;
>> +		}
>> +
> 
> As noted last time, the above is just busy work if pfn_list is not
> already empty.  The entire code block above should be moved to after
> the block below.  Thanks,
> 

pfn_list will be empty for IOMMU backed devices where all pages are 
pinned and mapped, but those should be reported as dirty. So moved it 
back above empty pfn_list check.

Thanks,
Kirti

> Alex
> 
>>   		if (!RB_EMPTY_ROOT(&dma->pfn_list)) {
>>   			struct vfio_iommu_type1_dma_unmap nb_unmap;
>>   
>> @@ -2447,17 +2477,40 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>>   
>>   	} else if (cmd == VFIO_IOMMU_UNMAP_DMA) {
>>   		struct vfio_iommu_type1_dma_unmap unmap;
>> -		long ret;
>> +		struct vfio_bitmap bitmap = { 0 };
>> +		int ret;
>>   
>>   		minsz = offsetofend(struct vfio_iommu_type1_dma_unmap, size);
>>   
>>   		if (copy_from_user(&unmap, (void __user *)arg, minsz))
>>   			return -EFAULT;
>>   
>> -		if (unmap.argsz < minsz || unmap.flags)
>> +		if (unmap.argsz < minsz ||
>> +		    unmap.flags & ~VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP)
>>   			return -EINVAL;
>>   
>> -		ret = vfio_dma_do_unmap(iommu, &unmap);
>> +		if (unmap.flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) {
>> +			unsigned long pgshift;
>> +
>> +			if (unmap.argsz < (minsz + sizeof(bitmap)))
>> +				return -EINVAL;
>> +
>> +			if (copy_from_user(&bitmap,
>> +					   (void __user *)(arg + minsz),
>> +					   sizeof(bitmap)))
>> +				return -EFAULT;
>> +
>> +			if (!access_ok((void __user *)bitmap.data, bitmap.size))
>> +				return -EINVAL;
>> +
>> +			pgshift = __ffs(bitmap.pgsize);
>> +			ret = verify_bitmap_size(unmap.size >> pgshift,
>> +						 bitmap.size);
>> +			if (ret)
>> +				return ret;
>> +		}
>> +
>> +		ret = vfio_dma_do_unmap(iommu, &unmap, &bitmap);
>>   		if (ret)
>>   			return ret;
>>   
>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>> index 123de3bc2dce..0a0c7315ddd6 100644
>> --- a/include/uapi/linux/vfio.h
>> +++ b/include/uapi/linux/vfio.h
>> @@ -1048,12 +1048,22 @@ struct vfio_bitmap {
>>    * field.  No guarantee is made to the user that arbitrary unmaps of iova
>>    * or size different from those used in the original mapping call will
>>    * succeed.
>> + * VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP should be set to get dirty bitmap
>> + * before unmapping IO virtual addresses. When this flag is set, user must
>> + * provide data[] as structure vfio_bitmap. User must allocate memory to get
>> + * bitmap, zero the bitmap memory and must set size of allocated memory in
>> + * vfio_bitmap.size field. A bit in bitmap represents one page of user provided
>> + * page size in 'pgsize', consecutively starting from iova offset. Bit set
>> + * indicates page at that offset from iova is dirty. Bitmap of pages in the
>> + * range of unmapped size is returned in vfio_bitmap.data
>>    */
>>   struct vfio_iommu_type1_dma_unmap {
>>   	__u32	argsz;
>>   	__u32	flags;
>> +#define VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP (1 << 0)
>>   	__u64	iova;				/* IO virtual address */
>>   	__u64	size;				/* Size of mapping (bytes) */
>> +	__u8    data[];
>>   };
>>   
>>   #define VFIO_IOMMU_UNMAP_DMA _IO(VFIO_TYPE, VFIO_BASE + 14)
>