* [PATCH v2] powerpc: warn on emulation of dcbz instruction in kernel mode
@ 2021-09-16 14:52 ` Christophe Leroy
0 siblings, 0 replies; 4+ messages in thread
From: Christophe Leroy @ 2021-09-16 14:52 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
Cc: Christophe Leroy, linux-kernel, linuxppc-dev, Stan Johnson, Finn Thain
dcbz instruction shouldn't be used on non-cached memory. Using
it on non-cached memory can result in alignment exception and
implies a heavy handling.
Instead of silentely emulating the instruction and resulting in high
performance degradation, warn whenever an alignment exception is
taken in kernel mode due to dcbz, so that the user is made aware that
dcbz instruction has been used unexpectedly by the kernel.
Reported-by: Stan Johnson <userm57@yahoo.com>
Cc: Finn Thain <fthain@linux-m68k.org>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
v2: Warn only when emulating kernel mode
---
arch/powerpc/kernel/align.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/powerpc/kernel/align.c b/arch/powerpc/kernel/align.c
index bbb4181621dd..bf96b954a4eb 100644
--- a/arch/powerpc/kernel/align.c
+++ b/arch/powerpc/kernel/align.c
@@ -349,6 +349,7 @@ int fix_alignment(struct pt_regs *regs)
if (op.type != CACHEOP + DCBZ)
return -EINVAL;
PPC_WARN_ALIGNMENT(dcbz, regs);
+ WARN_ON_ONCE(!user_mode(regs));
r = emulate_dcbz(op.ea, regs);
} else {
if (type == LARX || type == STCX)
--
2.31.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH v2] powerpc: warn on emulation of dcbz instruction in kernel mode
@ 2021-09-16 14:52 ` Christophe Leroy
0 siblings, 0 replies; 4+ messages in thread
From: Christophe Leroy @ 2021-09-16 14:52 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
Cc: Stan Johnson, Finn Thain, linuxppc-dev, linux-kernel
dcbz instruction shouldn't be used on non-cached memory. Using
it on non-cached memory can result in alignment exception and
implies a heavy handling.
Instead of silentely emulating the instruction and resulting in high
performance degradation, warn whenever an alignment exception is
taken in kernel mode due to dcbz, so that the user is made aware that
dcbz instruction has been used unexpectedly by the kernel.
Reported-by: Stan Johnson <userm57@yahoo.com>
Cc: Finn Thain <fthain@linux-m68k.org>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
v2: Warn only when emulating kernel mode
---
arch/powerpc/kernel/align.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/powerpc/kernel/align.c b/arch/powerpc/kernel/align.c
index bbb4181621dd..bf96b954a4eb 100644
--- a/arch/powerpc/kernel/align.c
+++ b/arch/powerpc/kernel/align.c
@@ -349,6 +349,7 @@ int fix_alignment(struct pt_regs *regs)
if (op.type != CACHEOP + DCBZ)
return -EINVAL;
PPC_WARN_ALIGNMENT(dcbz, regs);
+ WARN_ON_ONCE(!user_mode(regs));
r = emulate_dcbz(op.ea, regs);
} else {
if (type == LARX || type == STCX)
--
2.31.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2] powerpc: warn on emulation of dcbz instruction in kernel mode
2021-09-16 14:52 ` Christophe Leroy
@ 2021-11-02 10:11 ` Michael Ellerman
-1 siblings, 0 replies; 4+ messages in thread
From: Michael Ellerman @ 2021-11-02 10:11 UTC (permalink / raw)
To: Michael Ellerman, Paul Mackerras, Christophe Leroy,
Benjamin Herrenschmidt
Cc: Finn Thain, Stan Johnson, linux-kernel, linuxppc-dev
On Thu, 16 Sep 2021 16:52:09 +0200, Christophe Leroy wrote:
> dcbz instruction shouldn't be used on non-cached memory. Using
> it on non-cached memory can result in alignment exception and
> implies a heavy handling.
>
> Instead of silentely emulating the instruction and resulting in high
> performance degradation, warn whenever an alignment exception is
> taken in kernel mode due to dcbz, so that the user is made aware that
> dcbz instruction has been used unexpectedly by the kernel.
>
> [...]
Applied to powerpc/next.
[1/1] powerpc: warn on emulation of dcbz instruction in kernel mode
https://git.kernel.org/powerpc/c/cbe654c779616807e1e6823c3bdbfe07a10562b8
cheers
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] powerpc: warn on emulation of dcbz instruction in kernel mode
@ 2021-11-02 10:11 ` Michael Ellerman
0 siblings, 0 replies; 4+ messages in thread
From: Michael Ellerman @ 2021-11-02 10:11 UTC (permalink / raw)
To: Michael Ellerman, Paul Mackerras, Christophe Leroy,
Benjamin Herrenschmidt
Cc: linuxppc-dev, Stan Johnson, Finn Thain, linux-kernel
On Thu, 16 Sep 2021 16:52:09 +0200, Christophe Leroy wrote:
> dcbz instruction shouldn't be used on non-cached memory. Using
> it on non-cached memory can result in alignment exception and
> implies a heavy handling.
>
> Instead of silentely emulating the instruction and resulting in high
> performance degradation, warn whenever an alignment exception is
> taken in kernel mode due to dcbz, so that the user is made aware that
> dcbz instruction has been used unexpectedly by the kernel.
>
> [...]
Applied to powerpc/next.
[1/1] powerpc: warn on emulation of dcbz instruction in kernel mode
https://git.kernel.org/powerpc/c/cbe654c779616807e1e6823c3bdbfe07a10562b8
cheers
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-11-02 11:43 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2021-09-16 14:52 [PATCH v2] powerpc: warn on emulation of dcbz instruction in kernel mode Christophe Leroy
2021-09-16 14:52 ` Christophe Leroy
2021-11-02 10:11 ` Michael Ellerman
2021-11-02 10:11 ` Michael Ellerman
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