[PATCH v9 18/20] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0

Will Deacon
2021-06-08T18:04:56Z

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

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++
arch/arm64/kernel/cpufeature.c | 7 +++++++
2 files changed, 15 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb89dbdedc46..a2e453919bb6 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -287,6 +287,14 @@
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 only a strict
+ subset 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
+ and hot-unplug operations may be restricted.
+
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 854ade5b1de1..6f4aa006f130 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1298,6 +1298,13 @@ const struct cpumask *system_32bit_el0_cpumask(void)
return cpu_possible_mask;
}

+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 device *dev,
struct device_attribute *attr, char *buf)
{
--
2.32.0.rc1.229.g3e70b5a671-goog