[PATCH] arm64: kernel: disable CNP on Carmel

Rich Wiley rwiley at nvidia.com
Tue Feb 16 20:31:51 EST 2021

On NVIDIA Carmel cores, CNP behaves differently than it does on standard
ARM cores. On Carmel, if two cores have CNP enabled and share an L2 TLB
entry created by core0 for a specific ASID, a non-shareable TLBI from
core1 may still see the shared entry. On standard ARM cores, that TLBI
will invalidate the shared entry as well.

This causes issues with patchsets that attempt to do local TLBIs based
on cpumasks instead of broadcast TLBIs. Avoid these issues by disabling
CNP support for NVIDIA Carmel cores.

Signed-off-by: Rich Wiley <rwiley at nvidia.com>
 arch/arm64/kernel/cpufeature.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 9fac745aa7bb..2aa38a430f6a 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -986,6 +986,12 @@ static bool has_cache_dic(const struct arm64_cpu_capabilities *entry,
 	return ctr & BIT(CTR_DIC_SHIFT);
+static bool cpu_has_broken_cnp(void)
+	const struct midr_range range = MIDR_ALL_VERSIONS(MIDR_NVIDIA_CARMEL);
+	return is_midr_in_range(read_cpuid_id(), &range);
 static bool __maybe_unused
 has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope)
@@ -994,7 +1000,10 @@ has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope)
 	 * may share TLB entries with a CPU stuck in the crashed
 	 * kernel.
-	 if (is_kdump_kernel())
+	if (is_kdump_kernel())
+		return false;
+	if (cpu_has_broken_cnp())
 		return false;
 	return has_cpuid_feature(entry, scope);

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