2023-12-22 08:28:26

by Leonardo Bras

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

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 <[email protected]>
---
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; \
+ 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

2023-12-22 11:48:56

by Guo Ren

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

On Fri, Dec 22, 2023 at 4:27 PM Leonardo Bras <[email protected]> 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 <[email protected]>
> ---
> 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 <[email protected]>

> + 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

2023-12-22 17:26:06

by Leonardo Bras

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

On Fri, Dec 22, 2023 at 07:48:36PM +0800, Guo Ren wrote:
> On Fri, Dec 22, 2023 at 4:27 PM Leonardo Bras <[email protected]> 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 <[email protected]>
> > ---
> > 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 <[email protected]>

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
>