Re: [PATCH v17 Kernel 5/7] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap

[Kirti Wankhede <kwankhede@nvidia.com>]

On 3/31/2020 3:04 AM, Alex Williamson wrote:
> On Mon, 30 Mar 2020 22:20:42 +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
>> 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 | 55 ++++++++++++++++++++++++++++++++++++++---
>>   include/uapi/linux/vfio.h       | 10 ++++++++
>>   2 files changed, 61 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 5efebc2b60e1..266550bd7307 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -983,7 +983,8 @@ 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;
>> @@ -1034,6 +1035,10 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>   	 * will be returned if these conditions are not met.  The v2 interface
>>   	 * will only return success and a size of zero if there were no
>>   	 * mappings within the range.
>> +	 *
>> +	 * When VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP flag is set, unmap request
>> +	 * must be for single mapping. Multiple mappings with this flag set is
>> +	 * not supported.
>>   	 */
>>   	if (iommu->v2) {
>>   		dma = vfio_find_dma(iommu, unmap->iova, 1);
>> @@ -1041,6 +1046,14 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>   			ret = -EINVAL;
>>   			goto unlock;
>>   		}
>> +
>> +		if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
>> +		    dma &&
>> +		    (dma->iova != unmap->iova || dma->size != unmap->size)) {
> 
> 
> I think your intention was to return error if the user asked for the
> dirty bitmap and the requested unmap range doesn't exactly match the
> vfio_dma.  Not finding a vfio_dma should therefore also be an error.
> For example, if we had a single mapping at {0x1000-0x1fff} and the user
> unmapped with dirty bitmap {0x0-0x2fff}, that should return an error,
> but it's not caught by the above because there is no vfio_dma @0x0.
> Therefore I think you want:
> 
> ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
>   (!dma || dma->iova != unmap->iova || dma->size != unmap->size))
> 
> Right?  Thanks,
> 


Yes, updating check.

Is !dma here also error case when VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP 
flag is not set?
DMA_UNMAP ioctl returns how much was unmapped, from user space 
perspective this would be from start of range (unmap->iova), right?

Thanks,
Kirti