linux-kernel - [PATCH v8 3/7] mm/highmem: introduce clear_user

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Message-Id: <20251027202109.678022-4-ankur.a.arora@oracle.com>
Date: Mon, 27 Oct 2025 13:21:05 -0700
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@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        mjguzik@...il.com, luto@...nel.org, peterz@...radead.org,
        acme@...nel.org, namhyung@...nel.org, tglx@...utronix.de,
        willy@...radead.org, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        ankur.a.arora@...cle.com
Subject: [PATCH v8 3/7] mm/highmem: introduce clear_user_highpages()

Define clear_user_highpages() which clears pages sequentially using
the single page variant.

With !CONFIG_HIGHMEM, pages are contiguous so use the range clearing
primitive clear_user_pages().

Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>

Note: fixed
---
 include/linux/highmem.h | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 105cc4c00cc3..c5f8b1556fd7 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -199,6 +199,11 @@ static inline void invalidate_kernel_vmap_range(void *vaddr, int size)
 
 /* when CONFIG_HIGHMEM is not set these will be plain clear/copy_page */
 #ifndef clear_user_highpage
+/**
+ * clear_user_highpage() - clear a page to be mapped to user space
+ * @page: start page
+ * @vaddr: start address of the user mapping
+ */
 static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
 {
 	void *addr = kmap_local_page(page);
@@ -207,6 +212,30 @@ static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
 }
 #endif
 
+/**
+ * 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)
+{
+	if (!IS_ENABLED(CONFIG_HIGHMEM)) {
+		clear_user_pages(page_address(page), vaddr, page, npages);
+		return;
+	}
+
+	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.
-- 
2.43.5