linux-kernel - [PATCH] arm64: define __alloc_zeroed_user

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Message-Id: <20200312155920.50067-1-glider@google.com>
Date:   Thu, 12 Mar 2020 16:59:20 +0100
From:   glider@...gle.com
To:     catalin.marinas@....com, will.deacon@....com, mark.rutland@....com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        keescook@...omium.org, akpm@...ux-foundation.org,
        Alexander Potapenko <glider@...gle.com>
Subject: [PATCH] arm64: define __alloc_zeroed_user_highpage

When running the kernel with init_on_alloc=1, calling the default
implementation of __alloc_zeroed_user_highpage() from include/linux/highmem.h
leads to double-initialization of the allocated page (first by the page
allocator, then by clear_user_page().
Calling alloc_page_vma() with __GFP_ZERO, similarly to e.g. x86, seems
to be enough to ensure the user page is zeroed only once.

Signed-off-by: Alexander Potapenko <glider@...gle.com>
---
 arch/arm64/include/asm/page.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
index d39ddb258a049..75d6cd23a6790 100644
--- a/arch/arm64/include/asm/page.h
+++ b/arch/arm64/include/asm/page.h
@@ -21,6 +21,10 @@ extern void __cpu_copy_user_page(void *to, const void *from,
 extern void copy_page(void *to, const void *from);
 extern void clear_page(void *to);
 
+#define __alloc_zeroed_user_highpage(movableflags, vma, vaddr) \
+	alloc_page_vma(GFP_HIGHUSER | __GFP_ZERO | movableflags, vma, vaddr)
+#define __HAVE_ARCH_ALLOC_ZEROED_USER_HIGHPAGE
+
 #define clear_user_page(addr,vaddr,pg)  __cpu_clear_user_page(addr, vaddr)
 #define copy_user_page(to,from,vaddr,pg) __cpu_copy_user_page(to, from, vaddr)
 
-- 
2.25.1.481.gfbce0eb801-goog