Re: [PATCH V2 6/9] vfio/type1: implement interfaces to update vaddr

[Steven Sistare <steven.sistare@oracle.com>]

On 1/22/2021 4:48 PM, Alex Williamson wrote:
> On Tue, 19 Jan 2021 09:48:26 -0800
> Steve Sistare <steven.sistare@oracle.com> wrote:
> 
>> Implement VFIO_DMA_UNMAP_FLAG_VADDR, VFIO_DMA_MAP_FLAG_VADDR, and
>> VFIO_UPDATE_VADDR.  This is a partial implementation.  Blocking is
>> added in the next patch.
>>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>> ---
>>  drivers/vfio/vfio_iommu_type1.c | 54 ++++++++++++++++++++++++++++++++++++++---
>>  1 file changed, 51 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index ef83018..c307f62 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -92,6 +92,7 @@ struct vfio_dma {
>>  	int			prot;		/* IOMMU_READ/WRITE */
>>  	bool			iommu_mapped;
>>  	bool			lock_cap;	/* capable(CAP_IPC_LOCK) */
>> +	bool			vaddr_valid;
>>  	struct task_struct	*task;
>>  	struct rb_root		pfn_list;	/* Ex-user pinned pfn list */
>>  	unsigned long		*bitmap;
>> @@ -1101,6 +1102,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>  	dma_addr_t iova = unmap->iova;
>>  	unsigned long size = unmap->size;
>>  	bool unmap_all = !!(unmap->flags & VFIO_DMA_UNMAP_FLAG_ALL);
>> +	bool invalidate = !!(unmap->flags & VFIO_DMA_UNMAP_FLAG_VADDR);
>>  
>>  	mutex_lock(&iommu->lock);
>>  
>> @@ -1181,6 +1183,18 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>  		if (dma->task->mm != current->mm)
>>  			break;
>>  
>> +		if (invalidate) {
>> +			if (!dma->vaddr_valid)
>> +				goto unwind;
>> +			dma->vaddr_valid = false;
>> +			unmapped += dma->size;
>> +			size -= dma->iova + dma->size - iova;
>> +			iova = dma->iova + dma->size;
>> +			if (iova == 0)
>> +				break;
>> +			continue;
>> +		}
> 
> Clearly this is where the change to find-first semantics should have
> been introduced, the previous patch didn't require it.  Would it really
> be that unsightly to do:
> 
> while (1) {
> 	if (unlikely(invalidate))
> 		dma = vfio_find_dma_first(...
> 	else
> 		dma = vfio_find_dma(...
> 
> 	if (!dma)
> 		break;
> 
> Find-first followed by a tree walk might be more efficient, but of
> course requires a full loop redesign.

OK, I'll bite.  How about:

n = vfio_find_dma_first(iommu, iova, size);
while (n) {
        dma = rb_entry(n, struct vfio_dma, node);
        ...
        n = rb_next(n);
        vfio_remove_dma(iommu, dma);
}

plus similar changes in unwind.  This costs logN + N, eg O(N). 

For unmap-all, I could do find-any in constant time instead of logN and suppress the rb_next, 
but the code would be messier and the overall cost would still be O(N), so it does not seem worth it.

>> +
>>  		if (!RB_EMPTY_ROOT(&dma->pfn_list)) {
>>  			struct vfio_iommu_type1_dma_unmap nb_unmap;
>>  
>> @@ -1218,6 +1232,20 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>  		unmapped += dma->size;
>>  		vfio_remove_dma(iommu, dma);
>>  	}
>> +	goto unlock;
>> +
>> +unwind:
>> +	iova = unmap->iova;
>> +	size = unmap_all ? SIZE_MAX : unmap->size;
>> +	dma_last = dma;
>> +	while ((dma = vfio_find_dma_first(iommu, iova, size)) &&
>> +	       dma != dma_last) {
>> +		dma->vaddr_valid = true;
>> +		size -= dma->iova + dma->size - iova;
>> +		iova = dma->iova + dma->size;
>> +	}
>> +	ret = -EINVAL;
>> +	unmapped = 0;
>>  
>>  unlock:
>>  	mutex_unlock(&iommu->lock);
>> @@ -1319,6 +1347,7 @@ static bool vfio_iommu_iova_dma_valid(struct vfio_iommu *iommu,
>>  static int vfio_dma_do_map(struct vfio_iommu *iommu,
>>  			   struct vfio_iommu_type1_dma_map *map)
>>  {
>> +	bool update = map->flags & VFIO_DMA_MAP_FLAG_VADDR;
> 
> Please pick a slightly more specific variable name, update_vaddr maybe.
> Perhaps even clear_vaddr rather than invalidate above for consistency.

OK.

>>  	dma_addr_t iova = map->iova;
>>  	unsigned long vaddr = map->vaddr;
>>  	size_t size = map->size;
>> @@ -1336,13 +1365,16 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>>  	if (map->flags & VFIO_DMA_MAP_FLAG_READ)
>>  		prot |= IOMMU_READ;
>>  
>> +	if ((prot && update) || (!prot && !update))
>> +		return -EINVAL;
>> +
>>  	mutex_lock(&iommu->lock);
>>  
>>  	pgsize = (size_t)1 << __ffs(iommu->pgsize_bitmap);
>>  
>>  	WARN_ON((pgsize - 1) & PAGE_MASK);
>>  
>> -	if (!prot || !size || (size | iova | vaddr) & (pgsize - 1)) {
>> +	if (!size || (size | iova | vaddr) & (pgsize - 1)) {
>>  		ret = -EINVAL;
>>  		goto out_unlock;
>>  	}
>> @@ -1353,7 +1385,19 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>>  		goto out_unlock;
>>  	}
>>  
>> -	if (vfio_find_dma(iommu, iova, size)) {
>> +	dma = vfio_find_dma(iommu, iova, size);
>> +	if (update) {
>> +		if (!dma) {
>> +			ret = -ENOENT;
>> +		} else if (dma->vaddr_valid || dma->iova != iova ||
>> +			   dma->size != size) {
>> +			ret = -EINVAL;
>> +		} else {
>> +			dma->vaddr = vaddr;
>> +			dma->vaddr_valid = true;
>> +		}
>> +		goto out_unlock;
>> +	} else if (dma) {
>>  		ret = -EEXIST;
>>  		goto out_unlock;
>>  	}
>> @@ -1377,6 +1421,7 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>>  	iommu->dma_avail--;
>>  	dma->iova = iova;
>>  	dma->vaddr = vaddr;
>> +	dma->vaddr_valid = true;
>>  	dma->prot = prot;
>>  
>>  	/*
>> @@ -2545,6 +2590,7 @@ static int vfio_iommu_type1_check_extension(struct vfio_iommu *iommu,
>>  	case VFIO_TYPE1v2_IOMMU:
>>  	case VFIO_TYPE1_NESTING_IOMMU:
>>  	case VFIO_UNMAP_ALL:
>> +	case VFIO_UPDATE_VADDR:
>>  		return 1;
>>  	case VFIO_DMA_CC_IOMMU:
>>  		if (!iommu)
>> @@ -2699,7 +2745,8 @@ static int vfio_iommu_type1_map_dma(struct vfio_iommu *iommu,
>>  {
>>  	struct vfio_iommu_type1_dma_map map;
>>  	unsigned long minsz;
>> -	uint32_t mask = VFIO_DMA_MAP_FLAG_READ | VFIO_DMA_MAP_FLAG_WRITE;
>> +	uint32_t mask = VFIO_DMA_MAP_FLAG_READ | VFIO_DMA_MAP_FLAG_WRITE |
>> +			VFIO_DMA_MAP_FLAG_VADDR;
>>  
>>  	minsz = offsetofend(struct vfio_iommu_type1_dma_map, size);
>>  
>> @@ -2718,6 +2765,7 @@ static int vfio_iommu_type1_unmap_dma(struct vfio_iommu *iommu,
>>  	struct vfio_iommu_type1_dma_unmap unmap;
>>  	struct vfio_bitmap bitmap = { 0 };
>>  	uint32_t mask = VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP |
>> +			VFIO_DMA_UNMAP_FLAG_VADDR |
>>  			VFIO_DMA_UNMAP_FLAG_ALL;
> 
> dirty + vaddr would need a separate test per my previous patch comment.
> Thanks,

Yes.

- Steve