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

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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 <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Bug: 30369029
Patchset: kaslr-arm64-4.4

(cherry picked from commit 6d2aa549de1fc998581d216de3853aa131aa4446)
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Change-Id: I8c3bc8cdb7d7f7dea092fd1a208b04583a141054
This commit is contained in:
Ard Biesheuvel 2016-03-02 09:47:13 +01:00 • committed by Jeff Vander Stoep
parent 1c4143d40c
commit f41890295d
1 changed files with 7 additions and 0 deletions
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7
arch/arm64/mm/init.c
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@ -172,6 +172,13 @@ 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.
*/