Commit 6d2aa549 authored Mar 02, 2016 by Ard Biesheuvel Committed by Catalin Marinas Mar 02, 2016

arm64: mm: check at build time that PAGE_OFFSET divides the VA space evenly

Commit 8439e62a ("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 <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

parent 22b39ca3

arch/arm64/mm/init.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -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.
		*/

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