Re: [RFC 05/27] vhost: add helper for IOTLB entries shared page check

[Mike Pattrick <mkp@redhat.com>]

Hi Maxime,

On Fri, Mar 31, 2023 at 11:43 AM Maxime Coquelin
<maxime.coquelin@redhat.com> wrote:
>
> This patch introduces a helper to check whether two IOTLB
> entries share a page.
>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>  lib/vhost/iotlb.c | 25 ++++++++++++++++++++-----
>  1 file changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/lib/vhost/iotlb.c b/lib/vhost/iotlb.c
> index e8f1cb661e..d919f74704 100644
> --- a/lib/vhost/iotlb.c
> +++ b/lib/vhost/iotlb.c
> @@ -23,6 +23,23 @@ struct vhost_iotlb_entry {
>
>  #define IOTLB_CACHE_SIZE 2048
>
> +static bool
> +vhost_user_iotlb_share_page(struct vhost_iotlb_entry *a, struct vhost_iotlb_entry *b,
> +               uint64_t align)
> +{
> +       uint64_t a_end, b_start;
> +
> +       if (a == NULL || b == NULL)
> +               return false;
> +
> +       /* Assumes entry a lower than entry b */
> +       RTE_ASSERT(a->uaddr < b->uaddr);
> +       a_end = RTE_ALIGN_CEIL(a->uaddr + a->size, align);
> +       b_start = RTE_ALIGN_FLOOR(b->uaddr, align);
> +
> +       return a_end > b_start;

This may be a very minor detail, but it might improve readability if
the a_end calculation used addr + size - 1 and the return conditional
used >=.


Cheers,
M


> +}
> +
>  static void
>  vhost_user_iotlb_set_dump(struct virtio_net *dev, struct vhost_iotlb_entry *node)
>  {
> @@ -37,16 +54,14 @@ static void
>  vhost_user_iotlb_clear_dump(struct virtio_net *dev, struct vhost_iotlb_entry *node,
>                 struct vhost_iotlb_entry *prev, struct vhost_iotlb_entry *next)
>  {
> -       uint64_t align, mask;
> +       uint64_t align;
>
>         align = hua_to_alignment(dev->mem, (void *)(uintptr_t)node->uaddr);
> -       mask = ~(align - 1);
>
>         /* Don't disable coredump if the previous node is in the same page */
> -       if (prev == NULL || (node->uaddr & mask) != ((prev->uaddr + prev->size - 1) & mask)) {
> +       if (!vhost_user_iotlb_share_page(prev, node, align)) {
>                 /* Don't disable coredump if the next node is in the same page */
> -               if (next == NULL ||
> -                               ((node->uaddr + node->size - 1) & mask) != (next->uaddr & mask))
> +               if (!vhost_user_iotlb_share_page(node, next, align))
>                         mem_set_dump((void *)(uintptr_t)node->uaddr, node->size, false, align);
>         }
>  }
> --
> 2.39.2
>