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@arm.com> Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com> Link: https://lore.kernel.org/r/20230509142235.3284028-11-kristina.martsenko@arm.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
mariux64 · Jun 5, 2023 · 3e1dedb · 3e1dedb
1 parent b756412
commit 3e1dedb
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diff --git 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
@@ -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" },
 };