netdev - [PATCH v2] net: allow skb_datagram_iter to be called from any context

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Message-ID: <20240623081248.170613-1-sagi@grimberg.me>
Date: Sun, 23 Jun 2024 11:12:48 +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>,
	Sagi Grimberg <sagi@...mberg.me>
Subject: [PATCH v2] net: allow skb_datagram_iter to be called from any context

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:
- 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;
-- 
2.43.0