From 6d2aa549de1fc998581d216de3853aa131aa4446 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Wed, 2 Mar 2016 09:47:13 +0100 Subject: [PATCH 1/1] arm64: mm: check at build time that PAGE_OFFSET divides the VA space evenly Commit 8439e62a1561 ("arm64: mm: use bit ops rather than arithmetic in pa/va translations") changed the boundary check against PAGE_OFFSET from an arithmetic comparison to a bit test. This means we now silently assume that PAGE_OFFSET is a power of 2 that divides the kernel virtual address space into two equal halves. So make that assumption explicit. Signed-off-by: Ard Biesheuvel Signed-off-by: Catalin Marinas --- arch/arm64/mm/init.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index 22c6758b01aa..8c3d7dd91c25 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -170,6 +170,13 @@ void __init arm64_memblock_init(void) { const s64 linear_region_size = -(s64)PAGE_OFFSET; + /* + * Ensure that the linear region takes up exactly half of the kernel + * virtual address space. This way, we can distinguish a linear address + * from a kernel/module/vmalloc address by testing a single bit. + */ + BUILD_BUG_ON(linear_region_size != BIT(VA_BITS - 1)); + /* * Select a suitable value for the base of physical memory. */ -- 2.20.1