All of lore.kernel.org
 help / color / mirror / Atom feed
From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>,
	linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	Stan Johnson <userm57@yahoo.com>,
	Finn Thain <fthain@linux-m68k.org>
Subject: [PATCH v2] powerpc: warn on emulation of dcbz instruction in kernel mode
Date: Thu, 16 Sep 2021 16:52:09 +0200	[thread overview]
Message-ID: <2e3acfe63d289c6fba366e16973c9ab8369e8b75.1631803922.git.christophe.leroy@csgroup.eu> (raw)

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


WARNING: multiple messages have this Message-ID (diff)
From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>
Cc: Stan Johnson <userm57@yahoo.com>,
	Finn Thain <fthain@linux-m68k.org>,
	linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2] powerpc: warn on emulation of dcbz instruction in kernel mode
Date: Thu, 16 Sep 2021 16:52:09 +0200	[thread overview]
Message-ID: <2e3acfe63d289c6fba366e16973c9ab8369e8b75.1631803922.git.christophe.leroy@csgroup.eu> (raw)

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


             reply	other threads:[~2021-09-16 14:54 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-16 14:52 Christophe Leroy [this message]
2021-09-16 14:52 ` [PATCH v2] powerpc: warn on emulation of dcbz instruction in kernel mode Christophe Leroy
2021-11-02 10:11 ` Michael Ellerman
2021-11-02 10:11   ` 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=2e3acfe63d289c6fba366e16973c9ab8369e8b75.1631803922.git.christophe.leroy@csgroup.eu \
    --to=christophe.leroy@csgroup.eu \
    --cc=benh@kernel.crashing.org \
    --cc=fthain@linux-m68k.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=mpe@ellerman.id.au \
    --cc=paulus@samba.org \
    --cc=userm57@yahoo.com \
    /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.