From: Qais Yousef <qais.yousef@arm.com>
To: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org,
linux-kernel@vger.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>,
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: Re: [PATCH v4 12/14] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system
Date: Wed, 2 Dec 2020 18:08:27 +0000 [thread overview]
Message-ID: <20201202180827.7thdjnpnvfxh3s3r@e107158-lin.cambridge.arm.com> (raw)
In-Reply-To: <20201202174230.GA29939@willie-the-truck>
On 12/02/20 17:42, Will Deacon wrote:
> On Wed, Dec 02, 2020 at 12:59:52PM +0000, Qais Yousef wrote:
> > On 12/01/20 22:13, Will Deacon wrote:
> > > On Fri, Nov 27, 2020 at 01:41:22PM +0000, Qais Yousef wrote:
> > > > On 11/24/20 15:50, Will Deacon wrote:
> > > > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > > > > index 29017cbb6c8e..fe470683b43e 100644
> > > > > --- a/arch/arm64/kernel/cpufeature.c
> > > > > +++ b/arch/arm64/kernel/cpufeature.c
> > > > > @@ -1237,6 +1237,8 @@ has_cpuid_feature(const struct arm64_cpu_capabilities *entry, int scope)
> > > > >
> > > > > 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);
> > > > >
> > > > > @@ -1245,6 +1247,22 @@ static int enable_mismatched_32bit_el0(unsigned int cpu)
> > > > > static_branch_enable_cpuslocked(&arm64_mismatched_32bit_el0);
> > > > > }
> > > > >
> > > > > + if (cpumask_test_cpu(0, cpu_32bit_el0_mask) == cpu_32bit)
> > > > > + return 0;
> > > >
> > > > Hmm I'm struggling to get what you're doing here. You're treating CPU0 (the
> > > > boot CPU) specially here, but I don't get why?
> > >
> > > If our ability to execute 32-bit code is the same as the boot CPU then we
> > > don't have to do anything. That way, we can postpone nominating the lucky
> > > winner until we really need to.
> >
> > Okay I see what you're doing now. The '== cpu_32bit' part of the check gave me
> > trouble. If the first N cpus are 64bit only, we'll skip them here. Worth
> > a comment?
> >
> > Wouldn't it be better to replace this with a check if cpu_32bit_el0_mask is
> > empty instead? That would be a lot easier to read.
>
> Sorry, but I don't follow. What if all the CPUs are 32-bit capable?
You're right I missed this case.
--
Qais Yousef
next prev parent reply other threads:[~2020-12-02 18:09 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-24 15:50 [PATCH v4 00/14] An alternative series for asymmetric AArch32 systems Will Deacon
2020-11-24 15:50 ` [PATCH v4 01/14] arm64: cpuinfo: Split AArch32 registers out into a separate struct Will Deacon
2020-11-24 15:50 ` [PATCH v4 02/14] arm64: Allow mismatched 32-bit EL0 support Will Deacon
2020-11-27 10:25 ` Marc Zyngier
2020-11-27 11:50 ` Will Deacon
2020-11-27 13:09 ` Qais Yousef
2020-12-01 16:56 ` Will Deacon
2020-12-02 13:16 ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 03/14] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched " Will Deacon
2020-11-27 10:26 ` Marc Zyngier
2020-11-27 11:53 ` Will Deacon
2020-11-27 17:14 ` Marc Zyngier
2020-11-27 17:24 ` Quentin Perret
2020-11-27 18:16 ` Marc Zyngier
2020-12-01 16:57 ` Will Deacon
2020-12-02 8:18 ` Marc Zyngier
2020-12-02 17:27 ` Will Deacon
2020-11-24 15:50 ` [PATCH v4 04/14] arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs Will Deacon
2020-11-27 13:12 ` Qais Yousef
2020-12-01 16:56 ` Will Deacon
2020-12-02 13:52 ` Qais Yousef
2020-12-02 17:42 ` Will Deacon
2020-11-24 15:50 ` [PATCH v4 05/14] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Will Deacon
2020-11-24 15:50 ` [PATCH v4 06/14] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Will Deacon
2020-11-27 13:17 ` Qais Yousef
2020-12-01 16:56 ` Will Deacon
2020-11-24 15:50 ` [PATCH v4 07/14] sched: Introduce restrict_cpus_allowed_ptr() to limit task CPU affinity Will Deacon
2020-11-27 9:49 ` Quentin Perret
2020-11-27 13:19 ` Qais Yousef
2020-12-01 16:56 ` Will Deacon
2020-12-02 13:06 ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Will Deacon
2020-11-27 10:01 ` Quentin Perret
2020-11-27 13:23 ` Qais Yousef
2020-12-01 16:55 ` Will Deacon
2020-12-02 14:07 ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 09/14] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Will Deacon
2020-11-27 13:32 ` Qais Yousef
2020-11-30 17:05 ` Qais Yousef
2020-11-30 17:36 ` Quentin Perret
2020-12-01 11:58 ` Qais Yousef
2020-12-01 12:37 ` Quentin Perret
2020-12-01 14:11 ` Qais Yousef
2020-12-01 15:56 ` Quentin Perret
2020-12-01 22:30 ` Will Deacon
2020-12-02 11:34 ` Qais Yousef
2020-12-02 11:33 ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 10/14] sched: Introduce arch_task_cpu_possible_mask() to limit fallback rq selection Will Deacon
2020-11-24 15:50 ` [PATCH v4 11/14] sched: Reject CPU affinity changes based on arch_task_cpu_possible_mask() Will Deacon
2020-11-27 9:54 ` Quentin Perret
2020-11-24 15:50 ` [PATCH v4 12/14] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system Will Deacon
2020-11-27 13:41 ` Qais Yousef
2020-12-01 22:13 ` Will Deacon
2020-12-02 12:59 ` Qais Yousef
2020-12-02 17:42 ` Will Deacon
2020-12-02 18:08 ` Qais Yousef [this message]
2020-11-24 15:50 ` [PATCH v4 13/14] arm64: Implement arch_task_cpu_possible_mask() Will Deacon
2020-11-27 13:41 ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 14/14] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores Will Deacon
2020-11-27 13:58 ` [PATCH v4 00/14] An alternative series for asymmetric AArch32 systems Qais Yousef
2020-12-05 20:43 ` Pavel Machek
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