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Commit 8439e62a authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Catalin Marinas
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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: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent a92405f0

arch/arm64/include/asm/memory.h

+4 −3
Original line number Diff line number Diff line
@@ -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 & 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;