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 <[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
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))) \ > > 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
