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 <[email protected]> > --- > 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 > - 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))) \ > else \ > - mmap_end = VA_USER_SV39; \ > + mmap_end = (_addr + len); \ > mmap_end; \ > }) > > @@ -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))) \ > 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; \ > }) > > > -- > 2.43.0 > > > _______________________________________________ > linux-riscv mailing list > [email protected] > http://lists.infradead.org/mailman/listinfo/linux-riscv
