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From: Nick Desaulniers <ndesaulniers@google.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux@armlinux.org.uk, linux-arm-kernel@lists.infradead.org,
	linux-hardening@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Kees Cook <keescook@chromium.org>,
	Keith Packard <keithpac@amazon.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Marc Zyngier <maz@kernel.org>
Subject: Re: [PATCH v6 8/8] ARM: make get_current() and __my_cpu_offset() __always_inline
Date: Tue, 25 Jan 2022 12:48:29 -0800	[thread overview]
Message-ID: <CAKwvOdnV6ndTYjNN5CzYx_4LQpB4A6Qhfe21Vos192pUj=Hwmg@mail.gmail.com> (raw)
In-Reply-To: <20220125091453.1475246-9-ardb@kernel.org>

On Tue, Jan 25, 2022 at 1:15 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> The get_current() and __my_cpu_offset() accessors evaluate to only a
> single instruction emitted inline, but due to the size of the asm string
> that is created for SMP+v6 configurations, the compiler assumes
> otherwise, and may emit the functions out of line instead.
>
> So use __always_inline to avoid this.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Alternatively, you could use the inline qualifier on the asm stmt.
i.e. `asm inline ("my asm string")`. Only supported since gcc-8.3+ and
all kernel-supported versions of clang though. See `asm_inline` in
include/linux/compiler_types.h.
Either way,
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  arch/arm/include/asm/current.h | 2 +-
>  arch/arm/include/asm/percpu.h  | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/include/asm/current.h b/arch/arm/include/asm/current.h
> index 131a89bbec6b..1e1178bf176d 100644
> --- a/arch/arm/include/asm/current.h
> +++ b/arch/arm/include/asm/current.h
> @@ -14,7 +14,7 @@ struct task_struct;
>
>  extern struct task_struct *__current;
>
> -static inline __attribute_const__ struct task_struct *get_current(void)
> +static __always_inline __attribute_const__ struct task_struct *get_current(void)
>  {
>         struct task_struct *cur;
>
> diff --git a/arch/arm/include/asm/percpu.h b/arch/arm/include/asm/percpu.h
> index a09034ae45a1..7545c87c251f 100644
> --- a/arch/arm/include/asm/percpu.h
> +++ b/arch/arm/include/asm/percpu.h
> @@ -25,7 +25,7 @@ static inline void set_my_cpu_offset(unsigned long off)
>         asm volatile("mcr p15, 0, %0, c13, c0, 4" : : "r" (off) : "memory");
>  }
>
> -static inline unsigned long __my_cpu_offset(void)
> +static __always_inline unsigned long __my_cpu_offset(void)
>  {
>         unsigned long off;
>
> --
> 2.30.2
>


-- 
Thanks,
~Nick Desaulniers

WARNING: multiple messages have this Message-ID (diff)
From: Nick Desaulniers <ndesaulniers@google.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux@armlinux.org.uk, linux-arm-kernel@lists.infradead.org,
	 linux-hardening@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	 Kees Cook <keescook@chromium.org>,
	Keith Packard <keithpac@amazon.com>,
	 Linus Walleij <linus.walleij@linaro.org>,
	Marc Zyngier <maz@kernel.org>
Subject: Re: [PATCH v6 8/8] ARM: make get_current() and __my_cpu_offset() __always_inline
Date: Tue, 25 Jan 2022 12:48:29 -0800	[thread overview]
Message-ID: <CAKwvOdnV6ndTYjNN5CzYx_4LQpB4A6Qhfe21Vos192pUj=Hwmg@mail.gmail.com> (raw)
In-Reply-To: <20220125091453.1475246-9-ardb@kernel.org>

On Tue, Jan 25, 2022 at 1:15 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> The get_current() and __my_cpu_offset() accessors evaluate to only a
> single instruction emitted inline, but due to the size of the asm string
> that is created for SMP+v6 configurations, the compiler assumes
> otherwise, and may emit the functions out of line instead.
>
> So use __always_inline to avoid this.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Alternatively, you could use the inline qualifier on the asm stmt.
i.e. `asm inline ("my asm string")`. Only supported since gcc-8.3+ and
all kernel-supported versions of clang though. See `asm_inline` in
include/linux/compiler_types.h.
Either way,
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  arch/arm/include/asm/current.h | 2 +-
>  arch/arm/include/asm/percpu.h  | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/include/asm/current.h b/arch/arm/include/asm/current.h
> index 131a89bbec6b..1e1178bf176d 100644
> --- a/arch/arm/include/asm/current.h
> +++ b/arch/arm/include/asm/current.h
> @@ -14,7 +14,7 @@ struct task_struct;
>
>  extern struct task_struct *__current;
>
> -static inline __attribute_const__ struct task_struct *get_current(void)
> +static __always_inline __attribute_const__ struct task_struct *get_current(void)
>  {
>         struct task_struct *cur;
>
> diff --git a/arch/arm/include/asm/percpu.h b/arch/arm/include/asm/percpu.h
> index a09034ae45a1..7545c87c251f 100644
> --- a/arch/arm/include/asm/percpu.h
> +++ b/arch/arm/include/asm/percpu.h
> @@ -25,7 +25,7 @@ static inline void set_my_cpu_offset(unsigned long off)
>         asm volatile("mcr p15, 0, %0, c13, c0, 4" : : "r" (off) : "memory");
>  }
>
> -static inline unsigned long __my_cpu_offset(void)
> +static __always_inline unsigned long __my_cpu_offset(void)
>  {
>         unsigned long off;
>
> --
> 2.30.2
>


-- 
Thanks,
~Nick Desaulniers

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linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2022-01-25 20:49 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-25  9:14 [PATCH v6 0/8] ARM vmap'ed and IRQ stacks roundup Ard Biesheuvel
2022-01-25  9:14 ` Ard Biesheuvel
2022-01-25  9:14 ` [PATCH v6 1/8] ARM: mm: switch to swapper_pg_dir early for vmap'ed stack Ard Biesheuvel
2022-01-25  9:14   ` Ard Biesheuvel
2022-01-25  9:14 ` [PATCH v6 2/8] ARM: assembler: define a Kconfig symbol for group relocation support Ard Biesheuvel
2022-01-25  9:14   ` Ard Biesheuvel
2022-01-25  9:14 ` [PATCH v6 3/8] ARM: smp: elide HWCAP_TLS checks or __entry_task updates on SMP+v6 Ard Biesheuvel
2022-01-25  9:14   ` Ard Biesheuvel
2022-01-25  9:14 ` [PATCH v6 4/8] ARM: entry: avoid clobbering R9 in IRQ handler Ard Biesheuvel
2022-01-25  9:14   ` Ard Biesheuvel
2022-01-25  9:14 ` [PATCH v6 5/8] ARM: mm: make vmalloc_seq handling SMP safe Ard Biesheuvel
2022-01-25  9:14   ` Ard Biesheuvel
2022-01-25  9:14 ` [PATCH v6 6/8] ARM: iop: make iop_handle_irq() static Ard Biesheuvel
2022-01-25  9:14   ` Ard Biesheuvel
2022-01-25  9:14 ` [PATCH v6 7/8] ARM: drop pointless SMP check on secondary startup path Ard Biesheuvel
2022-01-25  9:14   ` Ard Biesheuvel
2022-01-25  9:14 ` [PATCH v6 8/8] ARM: make get_current() and __my_cpu_offset() __always_inline Ard Biesheuvel
2022-01-25  9:14   ` Ard Biesheuvel
2022-01-25 20:48   ` Nick Desaulniers [this message]
2022-01-25 20:48     ` Nick Desaulniers

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