linux-kernel - Re: [PATCH 2/6] arm64/vdso: Zap vvar pages when switching to a time namespace

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Message-ID: <d16b5cd1-bdb1-5667-fbda-c622cc795389@arista.com>
Date:   Tue, 16 Jun 2020 14:47:46 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     Mark Rutland <mark.rutland@....com>,
        Andrei Vagin <avagin@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/6] arm64/vdso: Zap vvar pages when switching to a time
 namespace

Hi Mark,

On 6/16/20 12:24 PM, Mark Rutland wrote:
> On Tue, Jun 16, 2020 at 12:55:41AM -0700, Andrei Vagin wrote:
[..]
>> Whenever a task changes its namespace, the VVAR
>> page tables are cleared and then they will be re-faulted with a
>> corresponding layout.
> 
> How does this work for multi-threaded applications? Are there any
> concerns w.r.t. atomicity of the change?

Multi-threaded applications can't setns() for time namespace,
timens_install():

:	if (!current_is_single_threaded())
:		return -EUSERS;

Thanks,
          Dmitry