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From:   Will Deacon <will@kernel.org>
To:     linux-arm-kernel@lists.infradead.org
Cc:     linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
        Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Marc Zyngier <maz@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Qais Yousef <qais.yousef@arm.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Quentin Perret <qperret@google.com>, Tejun Heo <tj@kernel.org>,
        Li Zefan <lizefan@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        kernel-team@android.com
Subject: [PATCH v5 14/15] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0
Date:   Tue,  8 Dec 2020 13:28:34 +0000
Message-Id: <20201208132835.6151-15-will@kernel.org>
In-Reply-To: <20201208132835.6151-1-will@kernel.org>
References: <20201208132835.6151-1-will@kernel.org>
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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 | 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 44fde25bb221..9d191e6e020b 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -289,6 +289,14 @@
 			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 08b558a221b7..fea0f213d55c 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1291,6 +1291,13 @@ 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)
 {
-- 
2.29.2.576.ga3fc446d84-goog