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Date: Thu, 19 Nov 2020 17:19:56 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Will Deacon <will@...nel.org> Cc: Quentin Perret <qperret@...gle.com>, linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org, Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Morten Rasmussen <morten.rasmussen@....com>, Qais Yousef <qais.yousef@....com>, Suren Baghdasaryan <surenb@...gle.com>, Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>, Johannes Weiner <hannes@...xchg.org>, Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, kernel-team@...roid.com Subject: Re: [PATCH v3 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 On Thu, Nov 19, 2020 at 11:06:04AM +0000, Will Deacon wrote: > On Thu, Nov 19, 2020 at 09:24:07AM +0000, Quentin Perret wrote: > > On Friday 13 Nov 2020 at 09:37:13 (+0000), Will Deacon wrote: > > > When exec'ing a 32-bit task on a system with mismatched support for > > > 32-bit EL0, try to ensure that it starts life on a CPU that can actually > > > run it. > > > > > > Signed-off-by: Will Deacon <will@...nel.org> > > > --- > > > arch/arm64/kernel/process.c | 12 +++++++++++- > > > 1 file changed, 11 insertions(+), 1 deletion(-) > > > > > > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > > > index 1540ab0fbf23..17b94007fed4 100644 > > > --- a/arch/arm64/kernel/process.c > > > +++ b/arch/arm64/kernel/process.c > > > @@ -625,6 +625,16 @@ unsigned long arch_align_stack(unsigned long sp) > > > return sp & ~0xf; > > > } > > > > > > +static void adjust_compat_task_affinity(struct task_struct *p) > > > +{ > > > + const struct cpumask *mask = system_32bit_el0_cpumask(); > > > + > > > + if (restrict_cpus_allowed_ptr(p, mask)) > > > + set_cpus_allowed_ptr(p, mask); > > > > My understanding of this call to set_cpus_allowed_ptr() is that you're > > mimicking the hotplug vs affinity case behaviour in some ways. That is, > > if a task is pinned to a CPU and userspace hotplugs that CPU, then the > > kernel will reset the affinity of the task to the remaining online CPUs. > > Correct. It looks to the 32-bit application like all the 64-bit-only CPUs > were hotplugged off at the point of the execve(). This doesn't respect cpusets though :/
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