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riscv: mm: Use hint address in mmap if available

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On riscv it is guaranteed that the address returned by mmap is less than
the hint address. Allow mmap to return an address all the way up to
addr, if provided, rather than just up to the lower address space.

This provides a performance benefit as well, allowing mmap to exit after
checking that the address is in range rather than searching for a valid
address.

It is possible to provide an address that uses at most the same number
of bits, however it is significantly more computationally expensive to
provide that number rather than setting the max to be the hint address.
There is the instruction clz/clzw in Zbb that returns the highest set bit
which could be used to performantly implement this, but it would still
be slower than the current implementation. At worst case, half of the
address would not be able to be allocated when a hint address is
provided.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20240130-use_mmap_hint_address-v3-1-8a655cfa8bcb@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Charlie Jenkins 2024-01-30 17:07:00 -08:00 • committed by Palmer Dabbelt
parent 556e2d17ca
commit b5b4287acc
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GPG key ID: 2E1319F35FBB1889
1 changed files with 11 additions and 16 deletions
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27
arch/riscv/include/asm/processor.h
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@ -14,22 +14,16 @@
#include <asm/ptrace.h>
#ifdef CONFIG_64BIT
#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1))
#define STACK_TOP_MAX TASK_SIZE_64
#define arch_get_mmap_end(addr, len, flags) \
({ \
unsigned long mmap_end; \
typeof(addr) _addr = (addr); \
if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
if ((_addr) == 0 || \
(IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \
((_addr + len) > BIT(VA_BITS - 1))) \
mmap_end = STACK_TOP_MAX; \
else if ((_addr) >= VA_USER_SV57) \
mmap_end = STACK_TOP_MAX; \
else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >= VA_BITS_SV48)) \
mmap_end = VA_USER_SV48; \
else \
mmap_end = VA_USER_SV39; \
mmap_end = (_addr + len); \
mmap_end; \
})
@ -39,17 +33,18 @@
typeof(addr) _addr = (addr); \
typeof(base) _base = (base); \
unsigned long rnd_gap = DEFAULT_MAP_WINDOW - (_base); \
if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
if ((_addr) == 0 || \
(IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \
((_addr + len) > BIT(VA_BITS - 1))) \
mmap_base = (_base); \
else if (((_addr) >= VA_USER_SV57) && (VA_BITS >= VA_BITS_SV57)) \
mmap_base = VA_USER_SV57 - rnd_gap; \
else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >= VA_BITS_SV48)) \
mmap_base = VA_USER_SV48 - rnd_gap; \
else \
mmap_base = VA_USER_SV39 - rnd_gap; \
mmap_base = (_addr + len) - rnd_gap; \
mmap_base; \
})
#ifdef CONFIG_64BIT
#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1))
#define STACK_TOP_MAX TASK_SIZE_64
#else
#define DEFAULT_MAP_WINDOW TASK_SIZE
#define STACK_TOP_MAX TASK_SIZE