[PATCH v2 3/3] arm64: Introduce command line parameter to disable CNP

Vladimir Murzin
2017-10-11T12:19:36Z

There are cases when activating of Common Not Private (CNP) feature
might not be desirable; this patch allows to forcefully disable CNP
even it is supported by hardware.

Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
---
Documentation/admin-guide/kernel-parameters.txt | 4 ++++
arch/arm64/kernel/cpufeature.c | 16 +++++++++++++++-
2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0549662..3c1e45d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2560,6 +2560,10 @@

noclflush [BUGS=X86] Don't use the CLFLUSH instruction

+ nocnp [ARM64]
+ Disable CNP (Common not Private translations)
+ even if it is supported by processor.
+
nodelayacct [KNL] Disable per-task delay accounting

nodsp [SH] Disable hardware DSP at boot time.
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 83809a8..9bceca3 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -771,6 +771,20 @@ static bool has_no_hw_prefetch(const struct arm64_cpu_capabilities *entry, int _
MIDR_CPU_VAR_REV(1, MIDR_REVISION_MASK));
}

+static bool nocnp;
+
+static int __init early_nocnp(char *p)
+{
+ nocnp = true;
+ return 0;
+}
+early_param("nocnp", early_nocnp);
+
+static bool has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope)
+{
+ return has_cpuid_feature(entry, scope) && !nocmp;
+}
+
static bool runs_at_el2(const struct arm64_cpu_capabilities *entry, int __unused)
{
return is_kernel_in_hyp_mode();
@@ -905,7 +919,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.desc = "Common not Private translations",
.capability = ARM64_HAS_CNP,
.def_scope = SCOPE_SYSTEM,
- .matches = has_cpuid_feature,
+ .matches = has_useable_cnp,
.sys_reg = SYS_ID_AA64MMFR2_EL1,
.sign = FTR_UNSIGNED,
.field_pos = ID_AA64MMFR2_CNP_SHIFT,
--
2.0.0