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

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>
This commit is contained in:
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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7
arch/arm64/include/asm/memory.h
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@ -88,10 +88,10 @@
*/
#define __virt_to_phys(x) ({ \
phys_addr_t __x = (phys_addr_t)(x); \
__x >= PAGE_OFFSET ? (__x - PAGE_OFFSET + PHYS_OFFSET) : \
(__x - kimage_voffset); })
__x & BIT(VA_BITS - 1) ? (__x & ~PAGE_OFFSET) + PHYS_OFFSET : \
(__x - kimage_voffset); })
#define __phys_to_virt(x) ((unsigned long)((x) - PHYS_OFFSET + PAGE_OFFSET))
#define __phys_to_virt(x) ((unsigned long)((x) - PHYS_OFFSET) | PAGE_OFFSET)
#define __phys_to_kimg(x) ((unsigned long)((x) + kimage_voffset))
/*
@ -132,6 +132,7 @@
#ifndef __ASSEMBLY__
#include <linux/bitops.h>
#include <linux/mmdebug.h>
extern phys_addr_t memstart_addr;