[PATCH 6/6] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0

[Will Deacon <will@kernel.org>]

Allow systems with mismatched 32-bit support at EL0 to run 32-bit
applications based on a new kernel parameter.

Signed-off-by: Will Deacon <will@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt | 7 +++++++
 arch/arm64/kernel/cpufeature.c                  | 7 +++++++
 2 files changed, 14 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 526d65d8573a..1d9021db4d9f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -289,6 +289,13 @@
 			do not want to use tracing_snapshot_alloc() as it needs
 			to be done where GFP_KERNEL allocations are allowed.
 
+	allow_mismatched_32bit_el0 [ARM64]
+			Allow execve() of 32-bit applications and setting of the
+			PER_LINUX32 personality on systems where not all of the
+			CPUs support 32-bit EL0. When this parameter is present,
+			the set of CPUs supporting 32-bit EL0 is indicated by
+			/sys/devices/system/cpu/aarch32_el0.
+
 	amd_iommu=	[HW,X86-64]
 			Pass parameters to the AMD IOMMU driver in the system.
 			Possible values are:
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 9f29d4d1ef7e..ccc08da443ec 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1237,6 +1237,13 @@ bool system_has_mismatched_32bit_el0(void)
 	return fld == ID_AA64PFR0_EL0_64BIT_ONLY;
 }
 
+static int __init parse_32bit_el0_param(char *str)
+{
+	__allow_mismatched_32bit_el0 = true;
+	return 0;
+}
+early_param("allow_mismatched_32bit_el0", parse_32bit_el0_param);
+
 static ssize_t aarch32_el0_show(struct kobject *kobj,
 				struct kobj_attribute *attr, char *buf)
 {
-- 
2.29.0.rc2.309.g374f81d7ae-goog