Checking whether memstart_addr has been assigned every time it is
referenced adds a branch instruction that may hurt performance if
the reference in question occurs on a hot path. So only perform the
check if CONFIG_DEBUG_VM=y.
Signed-off-by: Ard Biesheuvel <redacted>
---
arch/arm64/include/asm/memory.h | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 68e7d96b9ed3..771d0b506e4b 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -134,7 +134,11 @@
extern phys_addr_t memstart_addr;
/* PHYS_OFFSET - the physical address of the start of memory. */
+#ifndef CONFIG_DEBUG_VM
+#define PHYS_OFFSET ({ memstart_addr; })
+#else
#define PHYS_OFFSET ({ BUG_ON(memstart_addr & 1); memstart_addr; })
+#endif
/* the virtual base of the kernel image (minus TEXT_OFFSET) */
extern u64 kimage_vaddr;--
2.5.0
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 <redacted>
---
arch/arm64/include/asm/memory.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 771d0b506e4b..2296b32130a1 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -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))
/*@@ -131,6 +131,7 @@
#endif
#ifndef __ASSEMBLY__
+#include <linux/bitops.h>
extern phys_addr_t memstart_addr;
/* PHYS_OFFSET - the physical address of the start of memory. */
--
2.5.0