[PATCH v2 01/13] arm64/fpsimd: Avoid RES0 bits in the SME trap handler

[Mark Rutland <mark.rutland@arm.com>]

The SME trap handler consumes RES0 bits from the ESR when determining
the reason for the trap, and depends upon those bits reading as zero.
This may break in future when those RES0 bits are allocated a meaning
and stop reading as zero.

For SME traps taken with ESR_ELx.EC == 0b011101, the specific reason for
the trap is indicated by ESR_ELx.ISS.SMTC ("SME Trap Code"). This field
occupies bits [2:0] of ESR_ELx.ISS, and as of ARM DDI 0487 L.a, bits
[24:3] of ESR_ELx.ISS are RES0. ESR_ELx.ISS itself occupies bits [24:0]
of ESR_ELx.

Extract the SMTC field specifically, matching the way we handle ESR_ELx
fields elsewhere, and ensuring that the handler is future-proof.

Fixes: 8bd7f91c03d886f4 ("arm64/sme: Implement traps and syscall handling for SME")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/include/asm/esr.h | 14 ++++++++------
 arch/arm64/kernel/fpsimd.c   |  2 +-
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index d1b1a33f9a8b0..63aed18a933fe 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -371,12 +371,14 @@
 /*
  * ISS values for SME traps
  */
-
-#define ESR_ELx_SME_ISS_SME_DISABLED	0
-#define ESR_ELx_SME_ISS_ILL		1
-#define ESR_ELx_SME_ISS_SM_DISABLED	2
-#define ESR_ELx_SME_ISS_ZA_DISABLED	3
-#define ESR_ELx_SME_ISS_ZT_DISABLED	4
+#define ESR_ELx_SME_ISS_SMTC_MASK		GENMASK(2, 0)
+#define ESR_ELx_SME_ISS_SMTC(esr)		((esr) & ESR_ELx_SME_ISS_SMTC_MASK)
+
+#define ESR_ELx_SME_ISS_SMTC_SME_DISABLED	0
+#define ESR_ELx_SME_ISS_SMTC_ILL		1
+#define ESR_ELx_SME_ISS_SMTC_SM_DISABLED	2
+#define ESR_ELx_SME_ISS_SMTC_ZA_DISABLED	3
+#define ESR_ELx_SME_ISS_SMTC_ZT_DISABLED	4
 
 /* ISS field definitions for MOPS exceptions */
 #define ESR_ELx_MOPS_ISS_MEM_INST	(UL(1) << 24)
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 8370d55f03533..1ee5f330b8ed3 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1436,7 +1436,7 @@ void do_sme_acc(unsigned long esr, struct pt_regs *regs)
 	 * If this not a trap due to SME being disabled then something
 	 * is being used in the wrong mode, report as SIGILL.
 	 */
-	if (ESR_ELx_ISS(esr) != ESR_ELx_SME_ISS_SME_DISABLED) {
+	if (ESR_ELx_SME_ISS_SMTC(esr) != ESR_ELx_SME_ISS_SMTC_SME_DISABLED) {
 		force_signal_inject(SIGILL, ILL_ILLOPC, regs->pc, 0);
 		return;
 	}
-- 
2.30.2