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Message-ID: <36c8a5a8-94cd-4d81-9fef-125970c10ed5@grimberg.me>
Date: Sun, 23 Jun 2024 16:44:34 +0300
From: Sagi Grimberg <sagi@...mberg.me>
To: netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>
Cc: Eric Dumazet <edumazet@...gle.com>, David Howells <dhowells@...hat.com>,
Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2] net: allow skb_datagram_iter to be called from any
context
On 23/06/2024 11:12, Sagi Grimberg wrote:
> We only use the mapping in a single context, so kmap_local is sufficient
> and cheaper. Make sure to use skb_frag_foreach_page as skb frags may
> contain highmem compound pages and we need to map page by page.
>
> Signed-off-by: Sagi Grimberg <sagi@...mberg.me>
> ---
> Changes from v2:
Changes from v1 actually...
> - Fix usercopy BUG() due to copy from highmem pages across page boundary
> by using skb_frag_foreach_page
>
> net/core/datagram.c | 19 +++++++++++++------
> 1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/net/core/datagram.c b/net/core/datagram.c
> index a8b625abe242..cb72923acc21 100644
> --- a/net/core/datagram.c
> +++ b/net/core/datagram.c
> @@ -435,15 +435,22 @@ static int __skb_datagram_iter(const struct sk_buff *skb, int offset,
>
> end = start + skb_frag_size(frag);
> if ((copy = end - offset) > 0) {
> - struct page *page = skb_frag_page(frag);
> - u8 *vaddr = kmap(page);
> + u32 p_off, p_len, copied;
> + struct page *p;
> + u8 *vaddr;
>
> if (copy > len)
> copy = len;
> - n = INDIRECT_CALL_1(cb, simple_copy_to_iter,
> - vaddr + skb_frag_off(frag) + offset - start,
> - copy, data, to);
> - kunmap(page);
> +
> + skb_frag_foreach_page(frag,
> + skb_frag_off(frag) + offset - start,
> + copy, p, p_off, p_len, copied) {
> + vaddr = kmap_local_page(p);
> + n = INDIRECT_CALL_1(cb, simple_copy_to_iter,
> + vaddr + p_off, p_len, data, to);
> + kunmap_local(vaddr);
> + }
> +
> offset += n;
> if (n != copy)
> goto short_copy;
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