Re: [PATCH 3/6] vfio/iommu_type1: Initially set the pinned_page_dirty_scope

[Alex Williamson]

On Thu, 7 Jan 2021 12:43:58 +0800
Keqian Zhu <zhukeqian1@xxxxxxxxxx> wrote:

> For now there are 3 ways to promote the pinned_page_dirty_scope
> status of vfio_iommu:
> 
> 1. Through vfio pin interface.
> 2. Detach a group without pinned_dirty_scope.
> 3. Attach a group with pinned_dirty_scope.
> 
> For point 3, the only chance to promote the pinned_page_dirty_scope
> status is when vfio_iommu is newly created. As we can safely set
> empty vfio_iommu to be at pinned status, then the point 3 can be
> removed to reduce operations.
> 
> Signed-off-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 110ada24ee91..b596c482487b 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -2045,11 +2045,8 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>  			 * Non-iommu backed group cannot dirty memory directly,
>  			 * it can only use interfaces that provide dirty
>  			 * tracking.
> -			 * The iommu scope can only be promoted with the
> -			 * addition of a dirty tracking group.
>  			 */
>  			group->pinned_page_dirty_scope = true;
> -			promote_pinned_page_dirty_scope(iommu);
>  			mutex_unlock(&iommu->lock);
>  
>  			return 0;
> @@ -2436,6 +2433,7 @@ static void *vfio_iommu_type1_open(unsigned long arg)
>  	INIT_LIST_HEAD(&iommu->iova_list);
>  	iommu->dma_list = RB_ROOT;
>  	iommu->dma_avail = dma_entry_limit;
> +	iommu->pinned_page_dirty_scope = true;
>  	mutex_init(&iommu->lock);
>  	BLOCKING_INIT_NOTIFIER_HEAD(&iommu->notifier);
>  

This would be resolved automatically if we used the counter approach I
mentioned on the previous patch, adding a pinned-page scope group simply
wouldn't increment the iommu counter, which would initially be zero
indicating no "all-dma" groups.  Thanks,

Alex