On Mon, Jan 29, 2024 at 08:53:31PM -0500, Stefan O'Rear wrote:
On Mon, Jan 29, 2024, at 7:37 PM, Charlie Jenkins wrote:
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
arch/riscv/include/asm/processor.h | 21 ++++++++------------- 1 file changed, 8 insertions(+), 13 deletions(-)
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h index f19f861cda54..f3ea5166e3b2 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -22,14 +22,11 @@ ({ \ unsigned long mmap_end; \ typeof(addr) _addr = (addr); \
- if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
mmap_end = STACK_TOP_MAX; \Setting mmap_end in the no-hint case seems to have been lost?
-s
Thanks for catching that, will fix in v2.
- Charlie
- 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; \
- if ((_addr) == 0 || \
(IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \((_addr + len) > BIT(VA_BITS - 1))) \
mmap_end = VA_USER_SV39; \
mmap_end = (_addr + len); \})
@@ -39,14 +36,12 @@ 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))) \
- 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; \mmap_base = VA_USER_SV39 - rnd_gap; \
mmap_base = (_addr + len) - rnd_gap; \})
-- 2.43.0
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