diff mbox series

[v14,Kernel,2/7] vfio iommu: Remove atomicity of ref_count of pinned pages

Message ID 1584560474-19946-3-git-send-email-kwankhede@nvidia.com (mailing list archive)
State New, archived
Headers show
Series KABIs to support migration for VFIO devices | expand

Commit Message

Kirti Wankhede March 18, 2020, 7:41 p.m. UTC 
vfio_pfn.ref_count is always updated by holding iommu->lock, using atomic
variable is overkill.

Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
Reviewed-by: Neo Jia <cjia@nvidia.com>
---
 drivers/vfio/vfio_iommu_type1.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

Comments

Eric Auger March 23, 2020, 11:59 a.m. UTC | #1 
Hi Kirti,

On 3/18/20 8:41 PM, Kirti Wankhede wrote:
> vfio_pfn.ref_count is always updated by holding iommu->lock, using atomic
> variable is overkill.
> 
> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> Reviewed-by: Neo Jia <cjia@nvidia.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 9fdfae1cb17a..70aeab921d0f 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -112,7 +112,7 @@ struct vfio_pfn {
>  	struct rb_node		node;
>  	dma_addr_t		iova;		/* Device address */
>  	unsigned long		pfn;		/* Host pfn */
> -	atomic_t		ref_count;
> +	unsigned int		ref_count;
>  };
>  
>  struct vfio_regions {

> @@ -233,7 +233,7 @@ static int vfio_add_to_pfn_list(struct vfio_dma *dma, dma_addr_t iova,
>  
>  	vpfn->iova = iova;
>  	vpfn->pfn = pfn;
> -	atomic_set(&vpfn->ref_count, 1);
> +	vpfn->ref_count = 1;
>  	vfio_link_pfn(dma, vpfn);
>  	return 0;
>  }
> @@ -251,7 +251,7 @@ static struct vfio_pfn *vfio_iova_get_vfio_pfn(struct vfio_dma *dma,
>  	struct vfio_pfn *vpfn = vfio_find_vpfn(dma, iova);
>  
>  	if (vpfn)
> -		atomic_inc(&vpfn->ref_count);
> +		vpfn->ref_count++;
>  	return vpfn;
>  }
>  
> @@ -259,7 +259,8 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn *vpfn)
>  {
>  	int ret = 0;
>  
> -	if (atomic_dec_and_test(&vpfn->ref_count)) {
> +	vpfn->ref_count--;
> +	if (!vpfn->ref_count) {
>  		ret = put_pfn(vpfn->pfn, dma->prot);
>  		vfio_remove_from_pfn_list(dma, vpfn);
>  	}
> 

Reviewed-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric
diff mbox series

Patch

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 9fdfae1cb17a..70aeab921d0f 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -112,7 +112,7 @@  struct vfio_pfn {
 	struct rb_node		node;
 	dma_addr_t		iova;		/* Device address */
 	unsigned long		pfn;		/* Host pfn */
-	atomic_t		ref_count;
+	unsigned int		ref_count;
 };
 
 struct vfio_regions {
@@ -233,7 +233,7 @@  static int vfio_add_to_pfn_list(struct vfio_dma *dma, dma_addr_t iova,
 
 	vpfn->iova = iova;
 	vpfn->pfn = pfn;
-	atomic_set(&vpfn->ref_count, 1);
+	vpfn->ref_count = 1;
 	vfio_link_pfn(dma, vpfn);
 	return 0;
 }
@@ -251,7 +251,7 @@  static struct vfio_pfn *vfio_iova_get_vfio_pfn(struct vfio_dma *dma,
 	struct vfio_pfn *vpfn = vfio_find_vpfn(dma, iova);
 
 	if (vpfn)
-		atomic_inc(&vpfn->ref_count);
+		vpfn->ref_count++;
 	return vpfn;
 }
 
@@ -259,7 +259,8 @@  static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn *vpfn)
 {
 	int ret = 0;
 
-	if (atomic_dec_and_test(&vpfn->ref_count)) {
+	vpfn->ref_count--;
+	if (!vpfn->ref_count) {
 		ret = put_pfn(vpfn->pfn, dma->prot);
 		vfio_remove_from_pfn_list(dma, vpfn);
 	}