diff options
| author | Frederic Weisbecker <frederic@kernel.org> | 2024-10-25 00:12:59 +0200 |
|---|---|---|
| committer | Frederic Weisbecker <frederic@kernel.org> | 2025-01-08 18:13:29 +0100 |
| commit | 4a1567b466ecaa411cfe54c82009de7899e96171 (patch) | |
| tree | aee9abd95b0a5ed5e3091b24db621a86a603fe35 | |
| parent | 192faebeb9c35f9c34eeaf5227e616f3cc8099a0 (diff) | |
arm64: Exclude nohz_full CPUs from 32bits el0 support
Nohz full CPUs are not a desirable fallback target to run 32bits el0
applications. If present, prefer a set of housekeeping CPUs that can do
the job instead. Otherwise just don't support el0 32 bits. Should the
need arise, appropriate support can be introduced in the future.
Suggested-by: Will Deacon <will@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
| -rw-r--r-- | Documentation/arch/arm64/asymmetric-32bit.rst | 8 | ||||
| -rw-r--r-- | arch/arm64/kernel/cpufeature.c | 10 |
2 files changed, 17 insertions, 1 deletions
diff --git a/Documentation/arch/arm64/asymmetric-32bit.rst b/Documentation/arch/arm64/asymmetric-32bit.rst index 64a0b505da7d..1ca2b359a907 100644 --- a/Documentation/arch/arm64/asymmetric-32bit.rst +++ b/Documentation/arch/arm64/asymmetric-32bit.rst @@ -153,3 +153,11 @@ asymmetric system, a broken guest at EL1 could still attempt to execute mode will return to host userspace with an ``exit_reason`` of ``KVM_EXIT_FAIL_ENTRY`` and will remain non-runnable until successfully re-initialised by a subsequent ``KVM_ARM_VCPU_INIT`` operation. + +NOHZ FULL +--------- + +To avoid perturbing an adaptive-ticks CPU (specified using +``nohz_full=``) when a 32-bit task is forcefully migrated, these CPUs +are treated as 64-bit-only when support for asymmetric 32-bit systems +is enabled. diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 6ce71f444ed8..3c87659c14db 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -75,6 +75,7 @@ #include <linux/cpu.h> #include <linux/kasan.h> #include <linux/percpu.h> +#include <linux/sched/isolation.h> #include <asm/cpu.h> #include <asm/cpufeature.h> @@ -3742,7 +3743,14 @@ static int enable_mismatched_32bit_el0(unsigned int 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); + bool cpu_32bit = false; + + if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0)) { + if (!housekeeping_cpu(cpu, HK_TYPE_TICK)) + pr_info("Treating adaptive-ticks CPU %u as 64-bit only\n", cpu); + else + cpu_32bit = true; + } if (cpu_32bit) { cpumask_set_cpu(cpu, cpu_32bit_el0_mask); |