linux-kernel - [PATCH v10 2/8] highmem: introduce clear_user

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Message-Id: <20251215204922.475324-3-ankur.a.arora@oracle.com>
Date: Mon, 15 Dec 2025 12:49:16 -0800
From: Ankur Arora <ankur.a.arora@...cle.com>
To: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Cc: akpm@...ux-foundation.org, david@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        mjguzik@...il.com, luto@...nel.org, peterz@...radead.org,
        tglx@...utronix.de, willy@...radead.org, raghavendra.kt@....com,
        chleroy@...nel.org, ioworker0@...il.com, boris.ostrovsky@...cle.com,
        konrad.wilk@...cle.com, ankur.a.arora@...cle.com
Subject: [PATCH v10 2/8] highmem: introduce clear_user_highpages()

Define clear_user_highpages() which clears pages sequentially using
clear_user_highpage().

Also add a comment describing clear_user_highpage().

Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 include/linux/highmem.h | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 9a38512b8000..9187bfaa709d 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -217,7 +217,14 @@ static inline void clear_user_page(void *addr, unsigned long vaddr, struct page
 }
 #endif
 
-/* when CONFIG_HIGHMEM is not set these will be plain clear/copy_page */
+/**
+ * clear_user_highpage() - clear a page to be mapped to user space
+ * @page: start page
+ * @vaddr: start address of the user mapping
+ *
+ * With !CONFIG_HIGHMEM this (and the copy_user_highpage() below) will
+ * be plain clear_user_page() (and copy_user_page()).
+ */
 static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
 {
 	void *addr = kmap_local_page(page);
@@ -226,6 +233,25 @@ static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
 }
 #endif /* clear_user_highpage */
 
+/**
+ * clear_user_highpages() - clear a page range to be mapped to user space
+ * @page: start page
+ * @vaddr: start address of the user mapping
+ * @npages: number of pages
+ *
+ * Assumes that all the pages in the region (@page, +@...ges) are valid
+ * so this does no exception handling.
+ */
+static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
+					unsigned int npages)
+{
+	do {
+		clear_user_highpage(page, vaddr);
+		vaddr += PAGE_SIZE;
+		page++;
+	} while (--npages);
+}
+
 #ifndef vma_alloc_zeroed_movable_folio
 /**
  * vma_alloc_zeroed_movable_folio - Allocate a zeroed page for a VMA.
-- 
2.31.1