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Date: Fri, 24 Jan 2014 16:43:43 +0000
From: Will Deacon <will.deacon@arm.com>
To: Adrien =?iso-8859-1?Q?Verg=E9?= <adrienverge@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>,
        Catalin Marinas <Catalin.Marinas@arm.com>,
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	<linux-arm-kernel@lists.infradead.org>,
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Subject: Re: [PATCH V2 4/6] ARM: Make PID_IN_CONTEXTIDR incompatible with
 PID_NS
Message-ID: <20140124164343.GJ31040@mudshark.cambridge.arm.com>
References: <1390581656-16372-1-git-send-email-adrienverge@gmail.com>
 <1390581656-16372-5-git-send-email-adrienverge@gmail.com>
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On Fri, Jan 24, 2014 at 04:40:54PM +0000, Adrien Vergé wrote:
> When using namespaces, different processes can have the same PID.
> It makes no sense to store a PID value in the Context ID register
> to track a specific process, when others share the same value.
> 
> Consequently, PID_IN_CONTEXTIDR (which is used for tracing and
> debugging processes) should not be compatible with PID_NS.
> 
> Signed-off-by: Adrien Vergé <adrienverge@gmail.com>
> ---
>  arch/arm/Kconfig.debug   | 2 +-
>  arch/arm64/Kconfig.debug | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
> index 5765abf..ed46748 100644
> --- a/arch/arm/Kconfig.debug
> +++ b/arch/arm/Kconfig.debug
> @@ -1143,7 +1143,7 @@ config ARM_KPROBES_TEST
>  
>  config PID_IN_CONTEXTIDR
>  	bool "Write the current PID to the CONTEXTIDR register"
> -	depends on CPU_COPY_V6
> +	depends on CPU_COPY_V6 && !PID_NS
>  	help
>  	  Enabling this option causes the kernel to write the current PID to
>  	  the PROCID field of the CONTEXTIDR register, at the expense of some
> diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
> index 835c559..06b2633b 100644
> --- a/arch/arm64/Kconfig.debug
> +++ b/arch/arm64/Kconfig.debug
> @@ -17,6 +17,7 @@ config EARLY_PRINTK
>  
>  config PID_IN_CONTEXTIDR
>  	bool "Write the current PID to the CONTEXTIDR register"
> +	depends on !PID_NS
>  	help
>  	  Enabling this option causes the kernel to write the current PID to
>  	  the CONTEXTIDR register, at the expense of some additional

Are you sure about this? The value we write is actually task_pid_nr, which I
believe to be globally unique.

Will