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

Commit 8439e62a15 ("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>
This commit is contained in:
Ard Biesheuvel 2016-03-02 09:47:13 +01:00 committed by Catalin Marinas
parent 22b39ca3f2
commit 6d2aa549de
1 changed files with 7 additions and 0 deletions
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7
arch/arm64/mm/init.c
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@ -170,6 +170,13 @@ void __init arm64_memblock_init(void)
{ {
const s64 linear_region_size = -(s64)PAGE_OFFSET; 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. * Select a suitable value for the base of physical memory.
*/ */