mm/kmap: Add kmap_local_page_try_from_panic()

JIRA: https://issues.redhat.com/browse/RHEL-113576

commit 8702048
Author: Jocelyn Falempe <jfalempe@redhat.com>
Date:   Mon Apr 7 15:42:25 2025 +0200

    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@ffwll.ch>
    Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
    Link: https://lore.kernel.org/r/20250407140138.162383-2-jfalempe@redhat.com

Signed-off-by: José Expósito <jexposit@redhat.com>

Author: jexposit

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);
@@ -185,6 +193,11 @@ 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;