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Date:   Tue, 21 Sep 2021 16:41:45 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     sxwjean@me.com
Cc:     x86@kernel.org, linux-mm@kvack.org, tglx@linutronix.de,
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        christophe.leroy@csgroup.eu, linux-kernel@vger.kernel.org,
        Xiongwei Song <sxwjean@gmail.com>
Subject: Re: [PATCH RESEND 2/2] x86/mm: Randomize va with generic
 arch_pick_mmap_layout()
Message-ID: <YUnvKV0Qf6zhiasz@hirez.programming.kicks-ass.net>
References: <20210921143414.70723-1-sxwjean@me.com>
 <20210921143414.70723-3-sxwjean@me.com>
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On Tue, Sep 21, 2021 at 10:34:14PM +0800, sxwjean@me.com wrote:
> diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
> index 7516e4199b3c..c697e377644d 100644
> --- a/arch/x86/include/asm/compat.h
> +++ b/arch/x86/include/asm/compat.h
> @@ -151,6 +151,11 @@ struct compat_shmid64_ds {
>  	compat_ulong_t __unused5;
>  };
>  
> +static inline int is_compat_task(void)
> +{
> +	return IS_ENABLED(CONFIG_COMPAT) && test_thread_flag(TIF_32BIT);
> +}
> +

This is still fundamentally broken for x86. x86 doesn't have compat
tasks, the granularity is at syscall at best.