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Subject: Re: [PATCH v8 14/19] arm64: exec: Adjust affinity for compat tasks
 with mismatched 32-bit EL0
To:     Will Deacon <will@kernel.org>, linux-arm-kernel@lists.infradead.org
Cc:     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>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Valentin Schneider <valentin.schneider@arm.com>,
        kernel-team@android.com
References: <20210602164719.31777-1-will@kernel.org>
 <20210602164719.31777-15-will@kernel.org>
From:   Daniel Bristot de Oliveira <bristot@redhat.com>
Message-ID: <6594fc22-e99e-ee5e-c3ea-fb522e510b46@redhat.com>
Date:   Thu, 3 Jun 2021 11:45:10 +0200
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On 6/2/21 6:47 PM, 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.
> 
> Similarly, when exec'ing a 64-bit task on such a system, try to restore
> the old affinity mask if it was previously restricted.
> 
> Reviewed-by: Quentin Perret <qperret@google.com>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---

[...]

>  
> +#ifdef CONFIG_COMPAT
> +int compat_elf_check_arch(const struct elf32_hdr *hdr)
> +{
> +	if (!system_supports_32bit_el0())
> +		return false;
> +
> +	if ((hdr)->e_machine != EM_ARM)
> +		return false;
> +
> +	if (!((hdr)->e_flags & EF_ARM_EABI_MASK))
> +		return false;
> +
> +	/*
> +	 * Prevent execve() of a 32-bit program from a deadline task
> +	 * if the restricted affinity mask would be inadmissible on an
> +	 * asymmetric system.
> +	 */
> +	return !static_branch_unlikely(&arm64_mismatched_32bit_el0) ||
> +	       task_cpus_dl_admissible(current, system_32bit_el0_cpumask());
> +}
> +#endif

From the DL perspective:

Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>

Thanks!
-- Daniel