From: Catalin Marinas <catalin.marinas@xxxxxxx>
Currently, on an anonymous page fault, the kernel allocates a zeroed
page and maps it in user space. If the mapping is tagged (PROT_MTE),
set_pte_at() additionally clears the tags under a spinlock to avoid a
race on the page->flags. In order to optimise the lock, clear the page
tags on allocation in __alloc_zeroed_user_highpage() if the vma flags
have VM_MTE set.
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Steven Price <steven.price@xxxxxxx>
---
arch/arm64/include/asm/page.h | 6 ++++--
arch/arm64/mm/fault.c | 21 +++++++++++++++++++++
2 files changed, 25 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
index 012cffc574e8..97853570d0f1 100644
--- a/arch/arm64/include/asm/page.h
+++ b/arch/arm64/include/asm/page.h
@@ -13,6 +13,7 @@
#ifndef __ASSEMBLY__
#include <linux/personality.h> /* for READ_IMPLIES_EXEC */
+#include <linux/types.h>
#include <asm/pgtable-types.h>
struct page;
@@ -28,8 +29,9 @@ void copy_user_highpage(struct page *to, struct page *from,
void copy_highpage(struct page *to, struct page *from);
#define __HAVE_ARCH_COPY_HIGHPAGE
-#define __alloc_zeroed_user_highpage(movableflags, vma, vaddr) \
- alloc_page_vma(GFP_HIGHUSER | __GFP_ZERO | movableflags, vma, vaddr)
+struct page *__alloc_zeroed_user_highpage(gfp_t movableflags,
+ struct vm_area_struct *vma,
+ unsigned long vaddr);
#define __HAVE_ARCH_ALLOC_ZEROED_USER_HIGHPAGE
#define clear_user_page(page, vaddr, pg) clear_page(page)
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 871c82ab0a30..5a03428e97f3 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -921,3 +921,24 @@ void do_debug_exception(unsigned long addr_if_watchpoint, unsigned int esr,
debug_exception_exit(regs);
}
NOKPROBE_SYMBOL(do_debug_exception);
+
+/*
+ * Used during anonymous page fault handling.
+ */
+struct page *__alloc_zeroed_user_highpage(gfp_t movableflags,
+ struct vm_area_struct *vma,
+ unsigned long vaddr)
+{
+ struct page *page;
+ bool tagged = system_supports_mte() && (vma->vm_flags & VM_MTE);
+
+ page = alloc_page_vma(GFP_HIGHUSER | __GFP_ZERO | movableflags, vma,
+ vaddr);
+ if (tagged && page) {
+ mte_clear_page_tags(page_address(page));
+ page_kasan_tag_reset(page);
+ set_bit(PG_mte_tagged, &page->flags);
+ }
+
+ return page;
+}
--
2.20.1
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