linux-kernel - [PATCH 3.16 092/254] MIPS: clear MSACSR cause bits when handling MSA FP exception

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Date:   Wed, 28 Feb 2018 15:20:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, linux-mips@...ux-mips.org,
        "Ralf Baechle" <ralf@...ux-mips.org>,
        "Paul Burton" <paul.burton@...tec.com>
Subject: [PATCH 3.16 092/254] MIPS: clear MSACSR cause bits when handling
 MSA FP exception

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

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

From: Paul Burton <paul.burton@...tec.com>

commit 091be550a70a086c3b4420c6155e733dc410f190 upstream.

Much like for traditional scalar FP exceptions, the cause bits in the
MSACSR register need to be cleared following an MSA FP exception.
Without doing so the exception will simply be raised again whenever
the kernel restores MSACSR from a tasks saved context, leading to
undesirable spurious exceptions. Clear the cause bits from the
handle_msa_fpe function, mirroring the way handle_fpe clears the
cause bits in FCSR.

Signed-off-by: Paul Burton <paul.burton@...tec.com>
Cc: linux-mips@...ux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9164/
Signed-off-by: Ralf Baechle <ralf@...ux-mips.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/mips/kernel/genex.S | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/arch/mips/kernel/genex.S
+++ b/arch/mips/kernel/genex.S
@@ -368,6 +368,15 @@ NESTED(nmi_handler, PT_SIZE, sp)
 	STI
 	.endm
 
+	.macro	__build_clear_msa_fpe
+	_cfcmsa	a1, MSA_CSR
+	li	a2, ~(0x3f << 12)
+	and	a1, a1, a2
+	_ctcmsa	MSA_CSR, a1
+	TRACE_IRQS_ON
+	STI
+	.endm
+
 	.macro	__build_clear_ade
 	MFC0	t0, CP0_BADVADDR
 	PTR_S	t0, PT_BVADDR(sp)
@@ -426,7 +435,7 @@ NESTED(nmi_handler, PT_SIZE, sp)
 	BUILD_HANDLER cpu cpu sti silent		/* #11 */
 	BUILD_HANDLER ov ov sti silent			/* #12 */
 	BUILD_HANDLER tr tr sti silent			/* #13 */
-	BUILD_HANDLER msa_fpe msa_fpe sti silent	/* #14 */
+	BUILD_HANDLER msa_fpe msa_fpe msa_fpe silent	/* #14 */
 	BUILD_HANDLER fpe fpe fpe silent		/* #15 */
 	BUILD_HANDLER ftlb ftlb none silent		/* #16 */
 	BUILD_HANDLER msa msa sti silent		/* #21 */