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

Auger Eric
2020-03-23T11:59:28Z

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