[PATCH v2 1/5] arm64: Add override for ID_AA64ISAR1_EL1.LS64

[Fuad Tabba <fuad.tabba@linux.dev>]

Accesses to ACCDATA_EL1, which FEAT_LS64_ACCDATA adds, trap to EL3
unless firmware sets SCR_EL3.ADEn. Once KVM context-switches the
register for its guests, a host whose firmware leaves the bit clear
can't run them.

Add an override for ID_AA64ISAR1_EL1.LS64, with an arm64.nols64 alias,
so that the feature can be disabled on such a host and for its guests.
id_aa64isar1.ls64=2 disables only FEAT_LS64_ACCDATA and above.

Cc: stable@vger.kernel.org
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 Documentation/admin-guide/kernel-parameters.txt | 3 +++
 arch/arm64/kernel/pi/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 33cd30996e47e..ef690cf6c3664 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -571,6 +571,9 @@ Kernel parameters
 	arm64.nohaft	[ARM64] Unconditionally disable Hardware managed Access
 			Flag for Table descriptors support
 
+	arm64.nols64	[ARM64] Unconditionally disable 64-byte Load/Store
+			instructions support
+
 	arm64.nomops	[ARM64] Unconditionally disable Memory Copy and Memory
 			Set instructions support
 
diff --git a/arch/arm64/kernel/pi/idreg-override.c b/arch/arm64/kernel/pi/idreg-override.c
index 274bc72ba98d0..0c7f293779c1f 100644
--- a/arch/arm64/kernel/pi/idreg-override.c
+++ b/arch/arm64/kernel/pi/idreg-override.c
@@ -174,6 +174,7 @@ static const struct ftr_set_desc isar1 __prel64_initconst = {
 	.name		= "id_aa64isar1",
 	.override	= &id_aa64isar1_override,
 	.fields		= {
+		FIELD("ls64", ID_AA64ISAR1_EL1_LS64_SHIFT, NULL),
 		FIELD("gpi", ID_AA64ISAR1_EL1_GPI_SHIFT, NULL),
 		FIELD("gpa", ID_AA64ISAR1_EL1_GPA_SHIFT, NULL),
 		FIELD("api", ID_AA64ISAR1_EL1_API_SHIFT, NULL),
@@ -253,6 +254,7 @@ 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.nols64",		"id_aa64isar1.ls64=0" },
 	{ "arm64.nomops",		"id_aa64isar2.mops=0" },
 	{ "arm64.nomte",		"id_aa64pfr1.mte=0" },
 	{ "nokaslr",			"arm64_sw.nokaslr=1" },
-- 
2.47.3