* [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
@ 2021-08-20 5:16 Christophe Leroy
2021-08-20 12:15 ` Michael Ellerman
2021-08-27 13:15 ` Michael Ellerman
0 siblings, 2 replies; 5+ messages in thread
From: Christophe Leroy @ 2021-08-20 5:16 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
Cc: linux-kernel, linuxppc-dev
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.
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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
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 12:15 ` Michael Ellerman
2021-08-20 17:18 ` Segher Boessenkool
2021-08-27 13:15 ` Michael Ellerman
1 sibling, 1 reply; 5+ messages in thread
From: Michael Ellerman @ 2021-08-20 12:15 UTC (permalink / raw)
To: Christophe Leroy, Benjamin Herrenschmidt, Paul Mackerras
Cc: linux-kernel, linuxppc-dev
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
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
2021-08-20 12:15 ` Michael Ellerman
@ 2021-08-20 17:18 ` Segher Boessenkool
2021-08-20 18:12 ` Segher Boessenkool
0 siblings, 1 reply; 5+ messages in thread
From: Segher Boessenkool @ 2021-08-20 17:18 UTC (permalink / raw)
To: Michael Ellerman
Cc: Christophe Leroy, Benjamin Herrenschmidt, Paul Mackerras,
linuxppc-dev, linux-kernel
On Fri, Aug 20, 2021 at 10:15:11PM +1000, Michael Ellerman wrote:
> 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?
74xx do.
Segher
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
2021-08-20 17:18 ` Segher Boessenkool
@ 2021-08-20 18:12 ` Segher Boessenkool
0 siblings, 0 replies; 5+ messages in thread
From: Segher Boessenkool @ 2021-08-20 18:12 UTC (permalink / raw)
To: Michael Ellerman; +Cc: Paul Mackerras, linuxppc-dev, linux-kernel
On Fri, Aug 20, 2021 at 12:18:45PM -0500, Segher Boessenkool wrote:
> On Fri, Aug 20, 2021 at 10:15:11PM +1000, Michael Ellerman wrote:
> > 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?
>
> 74xx do.
7450 and later, that is. Will I ever get that right, sigh.
Segher
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
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 12:15 ` Michael Ellerman
@ 2021-08-27 13:15 ` Michael Ellerman
1 sibling, 0 replies; 5+ messages in thread
From: Michael Ellerman @ 2021-08-27 13:15 UTC (permalink / raw)
To: Michael Ellerman, Christophe Leroy, Paul Mackerras,
Benjamin Herrenschmidt
Cc: linuxppc-dev, linux-kernel
On Fri, 20 Aug 2021 05:16:05 +0000 (UTC), Christophe Leroy wrote:
> 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.
>
> This is not a performance critical path but this should be fixed for
> consistency.
>
> [...]
Applied to powerpc/next.
[1/1] powerpc/32: indirect function call use bctrl rather than blrl in ret_from_kernel_thread
https://git.kernel.org/powerpc/c/113ec9ccc8049c3772f0eab46b62c5d6654c09f7
cheers
^ permalink raw reply [flat|nested] 5+ messages in thread
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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 12:15 ` Michael Ellerman
2021-08-20 17:18 ` Segher Boessenkool
2021-08-20 18:12 ` Segher Boessenkool
2021-08-27 13:15 ` Michael Ellerman
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