linux-kernel - [PATCH 3.10 131/268] ARC: [arcompact] handle unaligned access delay slot corner case

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Message-Id: <1497897167-14556-132-git-send-email-w@1wt.eu>
Date:   Mon, 19 Jun 2017 20:30:30 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Vineet Gupta <vgupta@...opsys.com>, Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 131/268] ARC: [arcompact] handle unaligned access delay slot corner case

From: Vineet Gupta <vgupta@...opsys.com>

commit 9aed02feae57bf7a40cb04ea0e3017cb7a998db4 upstream.

After emulating an unaligned access in delay slot of a branch, we
pretend as the delay slot never happened - so return back to actual
branch target (or next PC if branch was not taken).

Curently we did this by handling STATUS32.DE, we also need to clear the
BTA.T bit, which is disregarded when returning from original misaligned
exception, but could cause weirdness if it took the interrupt return
path (in case interrupt was acive too)

One ARC700 customer ran into this when enabling unaligned access fixup
for kernel mode accesses as well

Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
Signed-off-by: Willy Tarreau <w@....eu>
---
 arch/arc/kernel/unaligned.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arc/kernel/unaligned.c b/arch/arc/kernel/unaligned.c
index 116d3e0..b13b422 100644
--- a/arch/arc/kernel/unaligned.c
+++ b/arch/arc/kernel/unaligned.c
@@ -228,8 +228,9 @@ int misaligned_fixup(unsigned long address, struct pt_regs *regs,
 	if (state.fault)
 		goto fault;
 
+	/* clear any remanants of delay slot */
 	if (delay_mode(regs)) {
-		regs->ret = regs->bta;
+		regs->ret = regs->bta ~1U;
 		regs->status32 &= ~STATUS_DE_MASK;
 	} else {
 		regs->ret += state.instr_len;
-- 
2.8.0.rc2.1.gbe9624a