Re: [PATCH] vhost: use bvec_kmap_local in {get,put}u16_iotlb

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On Tue, Feb 22, 2022 at 11:49 PM Christoph Hellwig <hch@xxxxxx> wrote:
>
> Using local kmaps slightly reduces the chances to stray writes, and
> the bvec interface cleans up the code a little bit.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>

Acked-by: Jason Wang <jasowang@xxxxxxxxxx>

> ---
>  drivers/vhost/vringh.c | 18 ++++++++----------
>  1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
> index 14e2043d76852..0f22a83fd09af 100644
> --- a/drivers/vhost/vringh.c
> +++ b/drivers/vhost/vringh.c
> @@ -1173,7 +1173,7 @@ static inline int getu16_iotlb(const struct vringh *vrh,
>                                u16 *val, const __virtio16 *p)
>  {
>         struct bio_vec iov;
> -       void *kaddr, *from;
> +       void *kaddr;
>         int ret;
>
>         /* Atomic read is needed for getu16 */
> @@ -1182,10 +1182,9 @@ static inline int getu16_iotlb(const struct vringh *vrh,
>         if (ret < 0)
>                 return ret;
>
> -       kaddr = kmap_atomic(iov.bv_page);
> -       from = kaddr + iov.bv_offset;
> -       *val = vringh16_to_cpu(vrh, READ_ONCE(*(__virtio16 *)from));
> -       kunmap_atomic(kaddr);
> +       kaddr = bvec_kmap_local(&iov);
> +       *val = vringh16_to_cpu(vrh, READ_ONCE(*(__virtio16 *)kaddr));
> +       kunmap_local(kaddr);
>
>         return 0;
>  }
> @@ -1194,7 +1193,7 @@ static inline int putu16_iotlb(const struct vringh *vrh,
>                                __virtio16 *p, u16 val)
>  {
>         struct bio_vec iov;
> -       void *kaddr, *to;
> +       void *kaddr;
>         int ret;
>
>         /* Atomic write is needed for putu16 */
> @@ -1203,10 +1202,9 @@ static inline int putu16_iotlb(const struct vringh *vrh,
>         if (ret < 0)
>                 return ret;
>
> -       kaddr = kmap_atomic(iov.bv_page);
> -       to = kaddr + iov.bv_offset;
> -       WRITE_ONCE(*(__virtio16 *)to, cpu_to_vringh16(vrh, val));
> -       kunmap_atomic(kaddr);
> +       kaddr = bvec_kmap_local(&iov);
> +       WRITE_ONCE(*(__virtio16 *)kaddr, cpu_to_vringh16(vrh, val));
> +       kunmap_local(kaddr);
>
>         return 0;
>  }
> --
> 2.30.2
>

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