linux-kernel - [PATCH v8 2/7] mm: introduce clear_pages() and clear_user

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Message-Id: <20251027202109.678022-3-ankur.a.arora@oracle.com>
Date: Mon, 27 Oct 2025 13:21:04 -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 2/7] mm: introduce clear_pages() and clear_user_pages()

Introduce clear_pages(), to be overridden by architectures that
support more efficient clearing of consecutive pages.

Also introduce clear_user_pages(), however, we will not expect
this function to be overridden anytime soon.

We have to place the clear_user_pages() variant that uses
clear_user_page() into mm/util.c for now to work around
macro magic on sparc and m68k.

Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 include/linux/mm.h | 41 +++++++++++++++++++++++++++++++++++++++++
 mm/util.c          | 13 +++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 683168b522b3..ecbcb76df9de 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3872,6 +3872,26 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
 				unsigned int order) {}
 #endif	/* CONFIG_DEBUG_PAGEALLOC */
 
+#ifndef __HAVE_ARCH_CLEAR_PAGES
+/**
+ * clear_pages() - clear a page range for kernel-internal use.
+ * @addr: start address
+ * @npages: number of pages
+ *
+ * Use clear_user_pages() instead when clearing a page range to be
+ * mapped to user space.
+ *
+ * Does absolutely no exception handling.
+ */
+static inline void clear_pages(void *addr, unsigned int npages)
+{
+	do {
+		clear_page(addr);
+		addr += PAGE_SIZE;
+	} while (--npages);
+}
+#endif
+
 #ifndef __HAVE_ARCH_CLEAR_USER_PAGE
 /**
  * clear_user_page() - clear a page to be mapped to user space
@@ -3894,6 +3914,27 @@ static inline void clear_user_page(void *addr, unsigned long vaddr, struct page
 }
 #endif
 
+/**
+ * clear_user_pages() - clear a page range to be mapped to user space
+ * @addr: start address
+ * @vaddr: start address of the user mapping
+ * @page: start page
+ * @npages: number of pages
+ *
+ * Assumes that the region (@addr, +@...ges) has been validated
+ * already so this does no exception handling.
+ */
+#ifdef __HAVE_ARCH_CLEAR_USER_PAGE
+void clear_user_pages(void *addr, unsigned long vaddr,
+		struct page *page, unsigned int npages);
+#else /* !__HAVE_ARCH_CLEAR_USER_PAGE */
+static inline void clear_user_pages(void *addr, unsigned long vaddr,
+		struct page *page, unsigned int npages)
+{
+	clear_pages(addr, npages);
+}
+#endif /* __HAVE_ARCH_CLEAR_USER_PAGE */
+
 #ifdef __HAVE_ARCH_GATE_AREA
 extern struct vm_area_struct *get_gate_vma(struct mm_struct *mm);
 extern int in_gate_area_no_mm(unsigned long addr);
diff --git a/mm/util.c b/mm/util.c
index 8989d5767528..d3b662b71f33 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1344,3 +1344,16 @@ bool page_range_contiguous(const struct page *page, unsigned long nr_pages)
 }
 EXPORT_SYMBOL(page_range_contiguous);
 #endif
+
+#ifdef __HAVE_ARCH_CLEAR_USER_PAGE
+void clear_user_pages(void *addr, unsigned long vaddr,
+		struct page *page, unsigned int npages)
+{
+	do {
+		clear_user_page(addr, vaddr, page);
+		addr += PAGE_SIZE;
+		vaddr += PAGE_SIZE;
+		page++;
+	} while (--npages);
+}
+#endif /* __HAVE_ARCH_CLEAR_USER_PAGE */
-- 
2.43.5