arm64: mm: use bit ops rather than arithmetic in pa/va translations

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Since PAGE_OFFSET is chosen such that it cuts the kernel VA space right
in half, and since the size of the kernel VA space itself is always a
power of 2, we can treat PAGE_OFFSET as a bitmask and replace the
additions/subtractions with 'or' and 'and-not' operations.

For the comparison against PAGE_OFFSET, a mov/cmp/branch sequence ends
up getting replaced with a single tbz instruction. For the additions and
subtractions, we save a mov instruction since the mask is folded into the
instruction's immediate field.

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

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Ard Biesheuvel 2016-02-22 18:46:04 +01:00 • committed by Catalin Marinas

parent a92405f082

commit 8439e62a15

1 changed files with 4 additions and 3 deletions

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arch/arm64/include/asm/memory.h

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