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From: Will Deacon <will@kernel.org>
To: Valentin Schneider <valentin.schneider@arm.com>
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>,
	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: Re: [PATCH v3 02/14] arm64: Allow mismatched 32-bit EL0 support
Date: Thu, 19 Nov 2020 13:12:37 +0000	[thread overview]
Message-ID: <20201119131236.GC4331@willie-the-truck> (raw)
In-Reply-To: <jhjblftwpqq.mognet@arm.com>

Hi Valentin,

Thanks for the review.

On Thu, Nov 19, 2020 at 11:27:41AM +0000, Valentin Schneider wrote:
> 
> On 13/11/20 09:37, Will Deacon wrote:
> > +const struct cpumask *system_32bit_el0_cpumask(void)
> > +{
> > +	if (!system_supports_32bit_el0())
> > +		return cpu_none_mask;
> > +
> > +	if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
> > +		return cpu_32bit_el0_mask;
> > +
> > +	return cpu_present_mask;
> > +}
> 
> Nit: this is used in patch 13 to implement arch_cpu_allowed_mask(). Since
> that latter defaults to cpu_possible_mask, this probably should too.

My original thinking was that, in a system where 32-bit EL0 support is
detected at boot and we're not handling mismatches, then it would be nice
to avoid saying that late CPUs are all 32-bit capable given that they will
fail to be onlined if they're not.

However, the reality is that we don't currently distinguish between the
present and possible masks on arm64 so it doesn't make any difference. It's
also not useful to userspace, because if the cores aren't online then so
what? Your observation above is another nail in the coffin, so I'll change
this to the possible mask as you suggest.

Cheers,

Will

  reply	other threads:[~2020-11-19 13:13 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-13  9:37 [PATCH v3 00/14] An alternative series for asymmetric AArch32 systems Will Deacon
2020-11-13  9:37 ` [PATCH v3 01/14] arm64: cpuinfo: Split AArch32 registers out into a separate struct Will Deacon
2020-11-13  9:37 ` [PATCH v3 02/14] arm64: Allow mismatched 32-bit EL0 support Will Deacon
2020-11-19 11:27   ` Valentin Schneider
2020-11-19 13:12     ` Will Deacon [this message]
2020-11-13  9:37 ` [PATCH v3 03/14] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched " Will Deacon
2020-11-13  9:37 ` [PATCH v3 04/14] arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs Will Deacon
2020-11-13  9:37 ` [PATCH v3 05/14] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Will Deacon
2020-11-13  9:37 ` [PATCH v3 06/14] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Will Deacon
2020-11-13  9:37 ` [PATCH v3 07/14] sched: Introduce restrict_cpus_allowed_ptr() to limit task CPU affinity Will Deacon
2020-11-19  9:18   ` Quentin Perret
2020-11-19 11:03     ` Quentin Perret
2020-11-19 11:05     ` Will Deacon
2020-11-19 11:27       ` Valentin Schneider
2020-11-19 13:13         ` Will Deacon
2020-11-19 14:54           ` Valentin Schneider
2020-11-19 16:41             ` Will Deacon
2020-11-19 12:47   ` Valentin Schneider
2020-11-19 13:13     ` Will Deacon
2020-11-19 14:54       ` Valentin Schneider
2020-11-19 16:09       ` Peter Zijlstra
2020-11-19 16:57         ` Valentin Schneider
2020-11-19 19:25           ` Will Deacon
2020-11-13  9:37 ` [PATCH v3 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Will Deacon
2020-11-19  9:24   ` Quentin Perret
2020-11-19 11:06     ` Will Deacon
2020-11-19 16:19       ` Peter Zijlstra
2020-11-19 16:30         ` Will Deacon
2020-11-19 16:44           ` Peter Zijlstra
2020-11-19 16:51             ` Will Deacon
2020-11-19 16:14   ` Peter Zijlstra
2020-11-19 16:28     ` Will Deacon
2020-11-19 16:42       ` Peter Zijlstra
2020-11-19 16:48         ` Will Deacon
2020-11-13  9:37 ` [PATCH v3 09/14] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Will Deacon
2020-11-19  9:29   ` Quentin Perret
2020-11-19 11:06     ` Will Deacon
2020-11-13  9:37 ` [PATCH v3 10/14] sched: Introduce arch_cpu_allowed_mask() to limit fallback rq selection Will Deacon
2020-11-19  9:38   ` Quentin Perret
2020-11-19 11:07     ` Will Deacon
2020-11-19 20:39       ` Will Deacon
2020-11-23 14:48         ` Quentin Perret
2020-11-13  9:37 ` [PATCH v3 11/14] sched: Reject CPU affinity changes based on arch_cpu_allowed_mask() Will Deacon
2020-11-19  9:47   ` Quentin Perret
2020-11-19 11:07     ` Will Deacon
2020-11-19 14:30       ` Quentin Perret
2020-11-19 16:44         ` Will Deacon
2020-11-13  9:37 ` [PATCH v3 12/14] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system Will Deacon
2020-11-13  9:37 ` [PATCH v3 13/14] arm64: Implement arch_cpu_allowed_mask() Will Deacon
2020-11-13  9:37 ` [PATCH v3 14/14] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores Will Deacon
2020-11-19 16:11 ` [PATCH v3 00/14] An alternative series for asymmetric AArch32 systems Peter Zijlstra
2020-11-19 16:39   ` Will Deacon

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