Re: [PATCH v15 Kernel 2/7] vfio iommu: Remove atomicity of ref_count of pinned pages

[Kirti Wankhede]

On 3/24/2020 2:00 AM, Auger Eric wrote:

Hi Kirti,

On 3/19/20 9:16 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 <kwankh...@nvidia.com>
Reviewed-by: Neo Jia <c...@nvidia.com>

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

Thanks.

Kirti.

Thanks

Eric

---
  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);
        }