linux-kernel - [PATCH 3.2 024/149] powerpc: Handle unaligned ldbrx/stdbrx

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Message-ID: <lsq.1382345188.730769455@decadent.org.uk>
Date:	Mon, 21 Oct 2013 09:46:28 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Anton Blanchard" <anton@...ba.org>,
	"Benjamin Herrenschmidt" <benh@...nel.crashing.org>
Subject: [PATCH 3.2 024/149] powerpc: Handle unaligned ldbrx/stdbrx

3.2.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Anton Blanchard <anton@...ba.org>

commit 230aef7a6a23b6166bd4003bfff5af23c9bd381f upstream.

Normally when we haven't implemented an alignment handler for
a load or store instruction the process will be terminated.

The alignment handler uses the DSISR (or a pseudo one) to locate
the right handler. Unfortunately ldbrx and stdbrx overlap lfs and
stfs so we incorrectly think ldbrx is an lfs and stdbrx is an
stfs.

This bug is particularly nasty - instead of terminating the
process we apply an incorrect fixup and continue on.

With more and more overlapping instructions we should stop
creating a pseudo DSISR and index using the instruction directly,
but for now add a special case to catch ldbrx/stdbrx.

Signed-off-by: Anton Blanchard <anton@...ba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/powerpc/kernel/align.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/arch/powerpc/kernel/align.c
+++ b/arch/powerpc/kernel/align.c
@@ -764,6 +764,16 @@ int fix_alignment(struct pt_regs *regs)
 	nb = aligninfo[instr].len;
 	flags = aligninfo[instr].flags;

+	/* ldbrx/stdbrx overlap lfs/stfs in the DSISR unfortunately */
+	if (IS_XFORM(instruction) && ((instruction >> 1) & 0x3ff) == 532) {
+		nb = 8;
+		flags = LD+SW;
+	} else if (IS_XFORM(instruction) &&
+		   ((instruction >> 1) & 0x3ff) == 660) {
+		nb = 8;
+		flags = ST+SW;
+	}
+
 	/* Byteswap little endian loads and stores */
 	swiz = 0;
 	if (regs->msr & MSR_LE) {

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