FAILED: patch "[PATCH] highmem: add folio_test_partial_kmap()" failed to apply to 6.6-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 97dfbbd135cb5e4426f37ca53a8fa87eaaa4e376
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025052622-segment-presuming-e4c6@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 97dfbbd135cb5e4426f37ca53a8fa87eaaa4e376 Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Date: Wed, 14 May 2025 18:06:02 +0100
Subject: [PATCH] highmem: add folio_test_partial_kmap()

In commit c749d9b7ebbc ("iov_iter: fix copy_page_from_iter_atomic() if
KMAP_LOCAL_FORCE_MAP"), Hugh correctly noted that if KMAP_LOCAL_FORCE_MAP
is enabled, we must limit ourselves to PAGE_SIZE bytes per call to
kmap_local().  The same problem exists in memcpy_from_folio(),
memcpy_to_folio(), folio_zero_tail(), folio_fill_tail() and
memcpy_from_file_folio(), so add folio_test_partial_kmap() to do this more
succinctly.

Link: https://lkml.kernel.org/r/20250514170607.3000994-2-willy@infradead.org
Fixes: 00cdf76012ab ("mm: add memcpy_from_file_folio()")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 5c6bea81a90e..c698f8415675 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -461,7 +461,7 @@ static inline void memcpy_from_folio(char *to, struct folio *folio,
 		const char *from = kmap_local_folio(folio, offset);
 		size_t chunk = len;
 
-		if (folio_test_highmem(folio) &&
+		if (folio_test_partial_kmap(folio) &&
 		    chunk > PAGE_SIZE - offset_in_page(offset))
 			chunk = PAGE_SIZE - offset_in_page(offset);
 		memcpy(to, from, chunk);
@@ -489,7 +489,7 @@ static inline void memcpy_to_folio(struct folio *folio, size_t offset,
 		char *to = kmap_local_folio(folio, offset);
 		size_t chunk = len;
 
-		if (folio_test_highmem(folio) &&
+		if (folio_test_partial_kmap(folio) &&
 		    chunk > PAGE_SIZE - offset_in_page(offset))
 			chunk = PAGE_SIZE - offset_in_page(offset);
 		memcpy(to, from, chunk);
@@ -522,7 +522,7 @@ static inline __must_check void *folio_zero_tail(struct folio *folio,
 {
 	size_t len = folio_size(folio) - offset;
 
-	if (folio_test_highmem(folio)) {
+	if (folio_test_partial_kmap(folio)) {
 		size_t max = PAGE_SIZE - offset_in_page(offset);
 
 		while (len > max) {
@@ -560,7 +560,7 @@ static inline void folio_fill_tail(struct folio *folio, size_t offset,
 
 	VM_BUG_ON(offset + len > folio_size(folio));
 
-	if (folio_test_highmem(folio)) {
+	if (folio_test_partial_kmap(folio)) {
 		size_t max = PAGE_SIZE - offset_in_page(offset);
 
 		while (len > max) {
@@ -597,7 +597,7 @@ static inline size_t memcpy_from_file_folio(char *to, struct folio *folio,
 	size_t offset = offset_in_folio(folio, pos);
 	char *from = kmap_local_folio(folio, offset);
 
-	if (folio_test_highmem(folio)) {
+	if (folio_test_partial_kmap(folio)) {
 		offset = offset_in_page(offset);
 		len = min_t(size_t, len, PAGE_SIZE - offset);
 	} else
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index e6a21b62dcce..3b814ce08331 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -615,6 +615,13 @@ FOLIO_FLAG(dropbehind, FOLIO_HEAD_PAGE)
 PAGEFLAG_FALSE(HighMem, highmem)
 #endif
 
+/* Does kmap_local_folio() only allow access to one page of the folio? */
+#ifdef CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP
+#define folio_test_partial_kmap(f)	true
+#else
+#define folio_test_partial_kmap(f)	folio_test_highmem(f)
+#endif
+
 #ifdef CONFIG_SWAP
 static __always_inline bool folio_test_swapcache(const struct folio *folio)
 {