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References: <20231222074605.452452-1-leobras@redhat.com> <20231222074605.452452-3-leobras@redhat.com>
 <CAJF2gTQNE7OQiAbkvVNzo9PCV=Xr8KQD0_=s-G56QMZJiZnjvA@mail.gmail.com> <ZYXDdlF1CFNpDdiV@LeoBras>
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From: Andy Chiu <andy.chiu@sifive.com>
Date: Sat, 23 Dec 2023 12:15:06 +0800
Message-ID: <CABgGipWmidzhf3PqyK9FWQCmKAuS9H31XECTL5XYjSL5m1Es4g@mail.gmail.com>
Subject: Re: [RFC PATCH 2/4] riscv: add compile-time test into is_compat_task()
To: Leonardo Bras <leobras@redhat.com>
Cc: Guo Ren <guoren@kernel.org>, Paul Walmsley <paul.walmsley@sifive.com>, 
	Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou <aou@eecs.berkeley.edu>, 
	Eric Biederman <ebiederm@xmission.com>, Kees Cook <keescook@chromium.org>, 
	Oleg Nesterov <oleg@redhat.com>, Conor Dooley <conor.dooley@microchip.com>, 
	Greg Ungerer <gerg@kernel.org>, Vincent Chen <vincent.chen@sifive.com>, 
	Xiao Wang <xiao.w.wang@intel.com>, Charlie Jenkins <charlie@rivosinc.com>, 
	Andrew Morton <akpm@linux-foundation.org>, Alexandre Ghiti <alexghiti@rivosinc.com>, 
	Kemeng Shi <shikemeng@huaweicloud.com>, David Hildenbrand <david@redhat.com>, 
	"Matthew Wilcox (Oracle)" <willy@infradead.org>, Qinglin Pan <panqinglin2020@iscas.ac.cn>, 
	Greentime Hu <greentime.hu@sifive.com>, =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@rivosinc.com>, 
	=?UTF-8?B?Q2zDqW1lbnQgTMOpZ2Vy?= <cleger@rivosinc.com>, 
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, 
	linux-mm@kvack.org
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On Sat, Dec 23, 2023 at 1:12=E2=80=AFAM Leonardo Bras <leobras@redhat.com> =
wrote:
>
> On Fri, Dec 22, 2023 at 05:35:20PM +0800, Guo Ren wrote:
> > On Fri, Dec 22, 2023 at 5:02=E2=80=AFPM Leonardo Bras <leobras@redhat.c=
om> wrote:
> > >
> > > Currently several places will test for CONFIG_COMPAT before testing
> > > is_compat_task(), probably in order to avoid a run-time test into the=
 task
> > > structure.
> > >
> > > Since is_compat_task() is an inlined function, it would be helpful to=
 add a
> > > compile-time test of CONFIG_COMPAT, making sure it always returns zer=
o when
> > > the option is not enabled during the kernel build.
> > >
> > > With this, the compiler is able to understand in build-time that
> > > is_compat_task() will always return 0, and optimize-out some of the e=
xtra
> > > code introduced by the option.
> > >
> > > This will also allow removing a lot #ifdefs that were introduced, and=
 make
> > > the code more clean.
> > >
> > > Signed-off-by: Leonardo Bras <leobras@redhat.com>
> > > ---
> > >  arch/riscv/include/asm/compat.h    | 3 +++
> > >  arch/riscv/include/asm/elf.h       | 4 ----
> > >  arch/riscv/include/asm/pgtable.h   | 6 ------
> > >  arch/riscv/include/asm/processor.h | 4 ++--
> > >  4 files changed, 5 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/arch/riscv/include/asm/compat.h b/arch/riscv/include/asm=
/compat.h
> > > index 2ac955b51148f..91517b51b8e27 100644
> > > --- a/arch/riscv/include/asm/compat.h
> > > +++ b/arch/riscv/include/asm/compat.h
> > > @@ -14,6 +14,9 @@
> > >
> > >  static inline int is_compat_task(void)
> > >  {
> > > +       if (!IS_ENABLED(CONFIG_COMPAT))
> > > +               return 0;
> > > +
> > >         return test_thread_flag(TIF_32BIT);
> > >  }
> > >
> > > diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/el=
f.h
> > > index 59a08367fddd7..2e88257cafaea 100644
> > > --- a/arch/riscv/include/asm/elf.h
> > > +++ b/arch/riscv/include/asm/elf.h
> > > @@ -53,13 +53,9 @@ extern bool compat_elf_check_arch(Elf32_Ehdr *hdr)=
;
> > >  #define ELF_ET_DYN_BASE                ((DEFAULT_MAP_WINDOW / 3) * 2=
)
> > >
> > >  #ifdef CONFIG_64BIT
> > > -#ifdef CONFIG_COMPAT
> > >  #define STACK_RND_MASK         (is_compat_task() ? \
> > >                                  0x7ff >> (PAGE_SHIFT - 12) : \
> > >                                  0x3ffff >> (PAGE_SHIFT - 12))
> > > -#else
> > > -#define STACK_RND_MASK         (0x3ffff >> (PAGE_SHIFT - 12))
> > > -#endif
> > >  #endif
> > >
> > >  /*
> > > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/as=
m/pgtable.h
> > > index 1d472b31e0cfe..ea5b269be223a 100644
> > > --- a/arch/riscv/include/asm/pgtable.h
> > > +++ b/arch/riscv/include/asm/pgtable.h
> > > @@ -127,16 +127,10 @@
> > >  #define VA_USER_SV48 (UL(1) << (VA_BITS_SV48 - 1))
> > >  #define VA_USER_SV57 (UL(1) << (VA_BITS_SV57 - 1))
> > >
> > > -#ifdef CONFIG_COMPAT
> > >  #define MMAP_VA_BITS_64 ((VA_BITS >=3D VA_BITS_SV48) ? VA_BITS_SV48 =
: VA_BITS)
> > >  #define MMAP_MIN_VA_BITS_64 (VA_BITS_SV39)
> > >  #define MMAP_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_VA_BITS=
_64)
> > >  #define MMAP_MIN_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_MIN=
_VA_BITS_64)
> > > -#else
> > > -#define MMAP_VA_BITS ((VA_BITS >=3D VA_BITS_SV48) ? VA_BITS_SV48 : V=
A_BITS)
> > > -#define MMAP_MIN_VA_BITS (VA_BITS_SV39)
> > > -#endif /* CONFIG_COMPAT */
> > > -
> > >  #else
> > >  #include <asm/pgtable-32.h>
> > >  #endif /* CONFIG_64BIT */
> > > diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/=
asm/processor.h
> > > index f19f861cda549..ed32e53e55999 100644
> > > --- a/arch/riscv/include/asm/processor.h
> > > +++ b/arch/riscv/include/asm/processor.h
> > > @@ -22,7 +22,7 @@
> > >  ({                                                             \
> > >         unsigned long mmap_end;                                 \
> > >         typeof(addr) _addr =3D (addr);                            \
> > > -       if ((_addr) =3D=3D 0 || (IS_ENABLED(CONFIG_COMPAT) && is_comp=
at_task())) \
> > > +       if ((_addr) =3D=3D 0 || is_compat_task())                   \
> > >                 mmap_end =3D STACK_TOP_MAX;                       \
> > >         else if ((_addr) >=3D VA_USER_SV57)                       \
> > >                 mmap_end =3D STACK_TOP_MAX;                       \
> > > @@ -39,7 +39,7 @@
> > >         typeof(addr) _addr =3D (addr);                            \
> > >         typeof(base) _base =3D (base);                            \
> > >         unsigned long rnd_gap =3D DEFAULT_MAP_WINDOW - (_base);   \
> > > -       if ((_addr) =3D=3D 0 || (IS_ENABLED(CONFIG_COMPAT) && is_comp=
at_task())) \
> > > +       if ((_addr) =3D=3D 0 || is_compat_task())                   \
> > >                 mmap_base =3D (_base);                            \
> > >         else if (((_addr) >=3D VA_USER_SV57) && (VA_BITS >=3D VA_BITS=
_SV57)) \
> > >                 mmap_base =3D VA_USER_SV57 - rnd_gap;             \
> > > --
> > > 2.43.0
> > >
> > Reviewed-by: Guo Ren <guoren@kernel.org>
>
> Thanks!
> Leo
>
> >
> > --
> > Best Regards
> >  Guo Ren
> >
>

Reviewed-by: Andy Chiu <andy.chiu@sifive.com>