linux-kernel - Re: [PATCH v4 13/14] arm64: Implement arch_task_cpu_possible

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Message-ID: <20201127134150.fzpasxm67umtv4ya@e107158-lin.cambridge.arm.com>
Date:   Fri, 27 Nov 2020 13:41:50 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Will Deacon <will@...nel.org>
Cc:     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>,
        Peter Zijlstra <peterz@...radead.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Quentin Perret <qperret@...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 v4 13/14] arm64: Implement arch_task_cpu_possible_mask()

On 11/24/20 15:50, Will Deacon wrote:
> Provide an implementation of arch_task_cpu_possible_mask() so that we
> can prevent 64-bit-only cores being added to the 'cpus_mask' for compat
> tasks on systems with mismatched 32-bit support at EL0,
> 
> Signed-off-by: Will Deacon <will@...nel.org>
> ---
>  arch/arm64/include/asm/mmu_context.h | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
> index 0672236e1aea..641dff35a56f 100644
> --- a/arch/arm64/include/asm/mmu_context.h
> +++ b/arch/arm64/include/asm/mmu_context.h

nit: wouldn't cpufeature.h be a better header? No strong opinion really, it
just looked weird to see this among memory management related code.

Cheers

--
Qais Yousef

> @@ -251,6 +251,19 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
>  #define deactivate_mm(tsk,mm)	do { } while (0)
>  #define activate_mm(prev,next)	switch_mm(prev, next, current)
>  
> +static inline const struct cpumask *
> +arch_task_cpu_possible_mask(struct task_struct *p)
> +{
> +	if (!static_branch_unlikely(&arm64_mismatched_32bit_el0))
> +		return cpu_possible_mask;
> +
> +	if (!is_compat_thread(task_thread_info(p)))
> +		return cpu_possible_mask;
> +
> +	return system_32bit_el0_cpumask();
> +}
> +#define arch_task_cpu_possible_mask	arch_task_cpu_possible_mask
> +
>  void verify_cpu_asid_bits(void);
>  void post_ttbr_update_workaround(void);
>  
> -- 
> 2.29.2.454.gaff20da3a2-goog
>