All of lore.kernel.org
 help / color / mirror / Atom feed
From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
Date: Fri, 20 Aug 2021 22:15:11 +1000	[thread overview]
Message-ID: <871r6oe2i8.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <91b1d242525307ceceec7ef6e832bfbacdd4501b.1629436472.git.christophe.leroy@csgroup.eu>

Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> Copied from commit 89bbe4c798bc ("powerpc/64: indirect function call
> use bctrl rather than blrl in ret_from_kernel_thread")
>
> blrl is not recommended to use as an indirect function call, as it may
> corrupt the link stack predictor.

Do we know if any 32-bit CPUs have a link stack predictor or similar?

cheers

> This is not a performance critical path but this should be fixed for
> consistency.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  arch/powerpc/kernel/entry_32.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index 0273a1349006..61fdd53cdd9a 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -161,10 +161,10 @@ ret_from_fork:
>  ret_from_kernel_thread:
>  	REST_NVGPRS(r1)
>  	bl	schedule_tail
> -	mtlr	r14
> +	mtctr	r14
>  	mr	r3,r15
>  	PPC440EP_ERR42
> -	blrl
> +	bctrl
>  	li	r3,0
>  	b	ret_from_syscall
>  
> -- 
> 2.25.0

WARNING: multiple messages have this Message-ID (diff)
From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
Date: Fri, 20 Aug 2021 22:15:11 +1000	[thread overview]
Message-ID: <871r6oe2i8.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <91b1d242525307ceceec7ef6e832bfbacdd4501b.1629436472.git.christophe.leroy@csgroup.eu>

Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> Copied from commit 89bbe4c798bc ("powerpc/64: indirect function call
> use bctrl rather than blrl in ret_from_kernel_thread")
>
> blrl is not recommended to use as an indirect function call, as it may
> corrupt the link stack predictor.

Do we know if any 32-bit CPUs have a link stack predictor or similar?

cheers

> This is not a performance critical path but this should be fixed for
> consistency.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  arch/powerpc/kernel/entry_32.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index 0273a1349006..61fdd53cdd9a 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -161,10 +161,10 @@ ret_from_fork:
>  ret_from_kernel_thread:
>  	REST_NVGPRS(r1)
>  	bl	schedule_tail
> -	mtlr	r14
> +	mtctr	r14
>  	mr	r3,r15
>  	PPC440EP_ERR42
> -	blrl
> +	bctrl
>  	li	r3,0
>  	b	ret_from_syscall
>  
> -- 
> 2.25.0

  reply	other threads:[~2021-08-20 12:15 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-20  5:16 [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread Christophe Leroy
2021-08-20  5:16 ` Christophe Leroy
2021-08-20 12:15 ` Michael Ellerman [this message]
2021-08-20 12:15   ` Michael Ellerman
2021-08-20 17:18   ` Segher Boessenkool
2021-08-20 17:18     ` Segher Boessenkool
2021-08-20 18:12     ` Segher Boessenkool
2021-08-20 18:12       ` Segher Boessenkool
2021-08-27 13:15 ` Michael Ellerman

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=871r6oe2i8.fsf@mpe.ellerman.id.au \
    --to=mpe@ellerman.id.au \
    --cc=benh@kernel.crashing.org \
    --cc=christophe.leroy@csgroup.eu \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=paulus@samba.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.