linux-kernel - Re: [PATCH 3/6] arm64/vdso: Add time namespace page

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Date:   Tue, 2 Jun 2020 20:29:17 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     Andrei Vagin <avagin@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/6] arm64/vdso: Add time namespace page

Hi Andrei,

On 6/2/20 7:02 PM, Andrei Vagin wrote:
[..]
> --- a/arch/arm64/include/asm/vdso.h
> +++ b/arch/arm64/include/asm/vdso.h
> @@ -12,6 +12,12 @@
>   */
>  #define VDSO_LBASE	0x0
>  
> +#ifdef CONFIG_TIME_NS
> +#define __VVAR_PAGES    2
> +#else
> +#define __VVAR_PAGES    1
> +#endif
> +
>  #ifndef __ASSEMBLY__

Not an issue as-is, but:

on x86 vdso+vvar is always the same size with/without CONFIG_TIME_NAMESPACE.

Timens page isn't allocated on !CONFIG_TIME_NAMESPACE, but vma is the
same size. Which simplifies criu/vdso migration between different kernel
configs.

Not any critical, but just to note..

Thanks,
          Dima