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Subject: Re: [PATCHv7 01/33] ns: Introduce Time Namespace
To:     Thomas Gleixner <tglx@linutronix.de>,
        Andrei Vagin <avagin@gmail.com>
Cc:     Dmitry Safonov <dima@arista.com>, linux-kernel@vger.kernel.org,
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        Pavel Emelyanov <xemul@virtuozzo.com>,
        Shuah Khan <shuah@kernel.org>,
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From:   Vincenzo Frascino <vincenzo.frascino@arm.com>
Message-ID: <406b77c3-46c5-e0ff-c658-04cdb99200b4@arm.com>
Date:   Thu, 17 Oct 2019 10:47:36 +0100
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On 10/17/19 10:20 AM, Thomas Gleixner wrote:

[...]

> The architectures which implement VDSO are:
> 
>     arm, arm64, mips, nds32, powerpc, riscv, s390, sparc, x86, um
> 
> arm64, mips, x86 use the generic VDSO. Patches for arm are floating
> around. UM is special as it just traps into the syscalls. No idea about the
> rest. Vincenzo might know.
> 

There a couple of cases: hexagon and csky that have vDSOs for signal trampolines
if I recall correctly, but they do not fall into the category we are exploring
at the moment.

> The bad news is that we have no information (except on arm which has a
> config switch for VDSO) whether an architecture provides VDSO support or
> not.
> 
> So unless you add something like
> 
>    config HAS_VDSO
>    	  bool
> 
> which is selected by all architectures which provide VDSO support, the only
> sane solution is to depend on GENERIC_VDSO_TIME_NS.
> 
> TBH, I would not even bother. The architectures which matter and are going
> to use time namespaces already support VDSO and they need to move to the
> generic implementation anyway as we discussed and agreed on in Vancouver.
> 
> Providing time name spaces for the non VDSO archs is a purely academic
> exercise.

I totally agree with this.

-- 
Regards,
Vincenzo