linux-kernel - [PATCH v2 10/11] arm64: mops: allow disabling MOPS from the kernel command line

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Message-Id: <20230509142235.3284028-11-kristina.martsenko@arm.com>
Date:   Tue,  9 May 2023 15:22:34 +0100
From:   Kristina Martsenko <kristina.martsenko@....com>
To:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        Luis Machado <luis.machado@....com>,
        Vladimir Murzin <vladimir.murzin@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 10/11] arm64: mops: allow disabling MOPS from the kernel command line

Make it possible to disable the MOPS extension at runtime using the
kernel command line. This can be useful for testing or working around
hardware issues. For example it could be used to test new memory copy
routines that do not use MOPS instructions (e.g. from Arm Optimized
Routines).

Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Kristina Martsenko <kristina.martsenko@....com>
---
 Documentation/admin-guide/kernel-parameters.txt | 3 +++
 arch/arm64/kernel/idreg-override.c              | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9e5bab29685f..e01fbfd78ae9 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -429,6 +429,9 @@
 	arm64.nosme	[ARM64] Unconditionally disable Scalable Matrix
 			Extension support
 
+	arm64.nomops	[ARM64] Unconditionally disable Memory Copy and Memory
+			Set instructions support
+
 	ataflop=	[HW,M68k]
 
 	atarimouse=	[HW,MOUSE] Atari Mouse
diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
index 370ab84fd06e..8439248c21d3 100644
--- a/arch/arm64/kernel/idreg-override.c
+++ b/arch/arm64/kernel/idreg-override.c
@@ -123,6 +123,7 @@ static const struct ftr_set_desc isar2 __initconst = {
 	.fields		= {
 		FIELD("gpa3", ID_AA64ISAR2_EL1_GPA3_SHIFT, NULL),
 		FIELD("apa3", ID_AA64ISAR2_EL1_APA3_SHIFT, NULL),
+		FIELD("mops", ID_AA64ISAR2_EL1_MOPS_SHIFT, NULL),
 		{}
 	},
 };
@@ -174,6 +175,7 @@ static const struct {
 	  "id_aa64isar1.gpi=0 id_aa64isar1.gpa=0 "
 	  "id_aa64isar1.api=0 id_aa64isar1.apa=0 "
 	  "id_aa64isar2.gpa3=0 id_aa64isar2.apa3=0"	   },
+	{ "arm64.nomops",		"id_aa64isar2.mops=0" },
 	{ "arm64.nomte",		"id_aa64pfr1.mte=0" },
 	{ "nokaslr",			"kaslr.disabled=1" },
 };
-- 
2.25.1