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Message-Id: <20210730112443.23245-13-will@kernel.org>
Date: Fri, 30 Jul 2021 12:24:39 +0100
From: Will Deacon <will@...nel.org>
To: linux-arm-kernel@...ts.infradead.org
Cc: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
Will Deacon <will@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Marc Zyngier <maz@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Peter Zijlstra <peterz@...radead.org>,
Morten Rasmussen <morten.rasmussen@....com>,
Qais Yousef <qais.yousef@....com>,
Suren Baghdasaryan <surenb@...gle.com>,
Quentin Perret <qperret@...gle.com>, Tejun Heo <tj@...nel.org>,
Johannes Weiner <hannes@...xchg.org>,
Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <valentin.schneider@....com>,
Mark Rutland <mark.rutland@....com>, kernel-team@...roid.com
Subject: [PATCH v11 12/16] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system
If we want to support 32-bit applications, then when we identify a CPU
with mismatched 32-bit EL0 support we must ensure that we will always
have an active 32-bit CPU available to us from then on. This is important
for the scheduler, because is_cpu_allowed() will be constrained to 32-bit
CPUs for compat tasks and forced migration due to a hotplug event will
hang if no 32-bit CPUs are available.
On detecting a mismatch, prevent offlining of either the mismatching CPU
if it is 32-bit capable, or find the first active 32-bit capable CPU
otherwise.
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Will Deacon <will@...nel.org>
---
arch/arm64/kernel/cpufeature.c | 25 ++++++++++++++++++++++++-
1 file changed, 24 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 125d5c9471ac..d99a29f52aa1 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2900,15 +2900,38 @@ void __init setup_cpu_features(void)
static int enable_mismatched_32bit_el0(unsigned int cpu)
{
+ /*
+ * The first 32-bit-capable CPU we detected and so can no longer
+ * be offlined by userspace. -1 indicates we haven't yet onlined
+ * a 32-bit-capable CPU.
+ */
+ static int lucky_winner = -1;
+
struct cpuinfo_arm64 *info = &per_cpu(cpu_data, cpu);
bool cpu_32bit = id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0);
if (cpu_32bit) {
cpumask_set_cpu(cpu, cpu_32bit_el0_mask);
static_branch_enable_cpuslocked(&arm64_mismatched_32bit_el0);
- setup_elf_hwcaps(compat_elf_hwcaps);
}
+ if (cpumask_test_cpu(0, cpu_32bit_el0_mask) == cpu_32bit)
+ return 0;
+
+ if (lucky_winner >= 0)
+ return 0;
+
+ /*
+ * We've detected a mismatch. We need to keep one of our CPUs with
+ * 32-bit EL0 online so that is_cpu_allowed() doesn't end up rejecting
+ * every CPU in the system for a 32-bit task.
+ */
+ lucky_winner = cpu_32bit ? cpu : cpumask_any_and(cpu_32bit_el0_mask,
+ cpu_active_mask);
+ get_cpu_device(lucky_winner)->offline_disabled = true;
+ setup_elf_hwcaps(compat_elf_hwcaps);
+ pr_info("Asymmetric 32-bit EL0 support detected on CPU %u; CPU hot-unplug disabled on CPU %u\n",
+ cpu, lucky_winner);
return 0;
}
--
2.32.0.402.g57bb445576-goog
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