[RFC PATCH 1/1] riscv: Improve arch_get_mmap_end() macro

[Leonardo Bras]

On Fri, Dec 22, 2023 at 07:48:36PM +0800, Guo Ren wrote:
> On Fri, Dec 22, 2023 at 4:27 PM Leonardo Bras <leobras at redhat.com> wrote:
> >
> > This macro caused me some confusion, which took some reviewer's time to
> > make it clear, so I propose adding a short comment in code to avoid
> > confusion in the future.
> >
> > Also, added some improvements to the macro, such as removing the
> > assumption of VA_USER_SV57 being the largest address space.
> >
> > Signed-off-by: Leonardo Bras <leobras at redhat.com>
> > ---
> >  arch/riscv/include/asm/processor.h | 12 +++++++++---
> >  1 file changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> > index f19f861cda549..2278e2a8362af 100644
> > --- a/arch/riscv/include/asm/processor.h
> > +++ b/arch/riscv/include/asm/processor.h
> > @@ -18,15 +18,21 @@
> >  #define DEFAULT_MAP_WINDOW     (UL(1) << (MMAP_VA_BITS - 1))
> >  #define STACK_TOP_MAX          TASK_SIZE_64
> >
> > +/*
> > + * addr is a hint to the maximum userspace address that mmap should provide, so
> > + * this macro needs to return the largest address space available so that
> > + * mmap_end < addr, being mmap_end the top of that address space.
> > + * See Documentation/arch/riscv/vm-layout.rst for more details.
> > + */
> >  #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())) \
> >                 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)) \
> > +       else if (((_addr) >= VA_USER_SV57) && (VA_BITS >= VA_BITS_SV57)) \
> > +               mmap_end = VA_USER_SV57;                        \
> It's clearer.
> 
> LGTM.
> Reviewed-by: Guo Ren <guoren at kernel.org>

Thanks!
Leo

> 
> > +       else if (((_addr) >= VA_USER_SV48) && (VA_BITS >= VA_BITS_SV48)) \
> >                 mmap_end = VA_USER_SV48;                        \
> >         else                                                    \
> >                 mmap_end = VA_USER_SV39;                        \
> > --
> > 2.43.0
> >
> 
> 
> -- 
> Best Regards
>  Guo Ren
>