linux-kernel - [PATCH v3 1/2] mm/kmap: Add kmap_local_page_try_from

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Message-ID: <20250407140138.162383-2-jfalempe@redhat.com>
Date: Mon,  7 Apr 2025 15:42:25 +0200
From: Jocelyn Falempe <jfalempe@...hat.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Ryosuke Yasuoka <ryasuoka@...hat.com>,
	Javier Martinez Canillas <javierm@...hat.com>,
	Wei Yang <richard.weiyang@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	John Ogness <john.ogness@...utronix.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-mm@...ck.org,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Cc: Jocelyn Falempe <jfalempe@...hat.com>,
	Simona Vetter <simona.vetter@...ll.ch>
Subject: [PATCH v3 1/2] mm/kmap: Add kmap_local_page_try_from_panic()

kmap_local_page() can be unsafe to call from a panic handler, if
CONFIG_HIGHMEM is set, and the page is in the highmem zone.
So add kmap_local_page_try_from_panic() to handle this case.

Suggested-by: Simona Vetter <simona.vetter@...ll.ch>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Jocelyn Falempe <jfalempe@...hat.com>
---

v3:
 * Add a comment in kmap_local_page_try_from_panic() (Thomas Gleixner)
 
 include/linux/highmem-internal.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/linux/highmem-internal.h b/include/linux/highmem-internal.h
index dd100e849f5e0..9a7683d79a4b1 100644
--- a/include/linux/highmem-internal.h
+++ b/include/linux/highmem-internal.h
@@ -73,6 +73,14 @@ static inline void *kmap_local_page(struct page *page)
 	return __kmap_local_page_prot(page, kmap_prot);
 }
 
+static inline void *kmap_local_page_try_from_panic(struct page *page)
+{
+	if (!PageHighMem(page))
+		return page_address(page);
+	/* If the page is in HighMem, it's not safe to kmap it.*/
+	return NULL;
+}
+
 static inline void *kmap_local_folio(struct folio *folio, size_t offset)
 {
 	struct page *page = folio_page(folio, offset / PAGE_SIZE);
@@ -180,6 +188,11 @@ static inline void *kmap_local_page(struct page *page)
 	return page_address(page);
 }
 
+static inline void *kmap_local_page_try_from_panic(struct page *page)
+{
+	return page_address(page);
+}
+
 static inline void *kmap_local_folio(struct folio *folio, size_t offset)
 {
 	return page_address(&folio->page) + offset;
-- 
2.49.0