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

[Auger Eric]

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 <address@hidden>
> Reviewed-by: Neo Jia <address@hidden>
Reviewed-by: Eric Auger <address@hidden>

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);
>       }
>