From mboxrd@z Thu Jan 1 00:00:00 1970 From: ard.biesheuvel@linaro.org (Ard Biesheuvel) Date: Wed, 2 Mar 2016 09:47:13 +0100 Subject: [PATCH] arm64: mm: check at build time that PAGE_OFFSET divides the VA space evenly Message-ID: <1456908433-27149-1-git-send-email-ard.biesheuvel@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 --- 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 9cfe94b41b54..ea136b904f56 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -171,6 +171,13 @@ 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. */ memstart_addr = round_down(memblock_start_of_DRAM(), -- 2.5.0