On Tue, 11 Apr 2023 at 15:03, Kal Conley <kal.conley@xxxxxxxxxxx> wrote:
>
> Remove redundant (base_addr >= pool->addrs_cnt) comparison from the
> conditional.
>
> In particular, addr is computed as:
>
> addr = base_addr + offset
>
> where base_addr and offset are stored as 48-bit and 16-bit unsigned
> integers, respectively. The above sum cannot overflow u64 since
> base_addr has a maximum value of 0x0000ffffffffffff and offset has a
> maximum value of 0xffff (implying a maximum sum of 0x000100000000fffe).
> Since overflow is impossible, it follows that addr >= base_addr.
>
> Now if (base_addr >= pool->addrs_cnt), then clearly:
>
> addr >= base_addr
> >= pool->addrs_cnt
>
> Thus, (base_addr >= pool->addrs_cnt) implies (addr >= pool->addrs_cnt).
> Subsequently, the former comparison is unnecessary in the conditional
> since for any boolean expressions A and B, (A || B) && (A -> B) is
> equivalent to B.
Thanks Kal! Just checking again that you ran the xsk selftests on your
change and that it passed? If so, here is my ack.
Acked-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
> Signed-off-by: Kal Conley <kal.conley@xxxxxxxxxxx>
> ---
> net/xdp/xsk_queue.h | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
> index 66c6f57c9c44..dea4f378327d 100644
> --- a/net/xdp/xsk_queue.h
> +++ b/net/xdp/xsk_queue.h
> @@ -153,16 +153,12 @@ static inline bool xp_aligned_validate_desc(struct xsk_buff_pool *pool,
> static inline bool xp_unaligned_validate_desc(struct xsk_buff_pool *pool,
> struct xdp_desc *desc)
> {
> - u64 addr, base_addr;
> -
> - base_addr = xp_unaligned_extract_addr(desc->addr);
> - addr = xp_unaligned_add_offset_to_addr(desc->addr);
> + u64 addr = xp_unaligned_add_offset_to_addr(desc->addr);
>
> if (desc->len > pool->chunk_size)
> return false;
>
> - if (base_addr >= pool->addrs_cnt || addr >= pool->addrs_cnt ||
> - addr + desc->len > pool->addrs_cnt ||
> + if (addr >= pool->addrs_cnt || addr + desc->len > pool->addrs_cnt ||
> xp_desc_crosses_non_contig_pg(pool, addr, desc->len))
> return false;
>
> --
> 2.39.2
>
