netdev - [PATCH net 1/3] net: support kmap_local forced debugging in skb_frag

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Date:   Fri,  8 Jan 2021 12:11:50 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org,
        Willem de Bruijn <willemb@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH net 1/3] net: support kmap_local forced debugging in skb_frag_foreach

From: Willem de Bruijn <willemb@...gle.com>

Skb frags may be backed by highmem and/or compound pages. Highmem
pages need kmap_atomic mappings to access. But kmap_atomic maps a
single page, not the entire compound page.

skb_foreach_page iterates over an skb frag, in one step in the common
case, page by page only if kmap_atomic must be called for each page.
The decision logic is captured in skb_frag_must_loop.

CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP extends kmap from highmem to all
pages, to increase code coverage.

Extend skb_frag_must_loop to this new condition.

Link: https://lore.kernel.org/linux-mm/20210106180132.41dc249d@gandalf.local.home/
Fixes: 0e91a0c6984c ("mm/highmem: Provide CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP")
Reported-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Willem de Bruijn <willemb@...gle.com>
Tested-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 include/linux/skbuff.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 333bcdc39635..c858adfb5a82 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -366,7 +366,7 @@ static inline void skb_frag_size_sub(skb_frag_t *frag, int delta)
 static inline bool skb_frag_must_loop(struct page *p)
 {
 #if defined(CONFIG_HIGHMEM)
-	if (PageHighMem(p))
+	if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP) || PageHighMem(p))
 		return true;
 #endif
 	return false;
-- 
2.30.0.284.gd98b1dd5eaa7-goog