linux-kernel - Re: [PATCH] x86: Remove hpet vclock support

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Message-ID: <CALCETrVKfykqOP=+LPwCRh5H4SJvzsDb8pa2uZ=UBiOx22RdCg@mail.gmail.com>
Date:	Sat, 1 Feb 2014 09:10:51 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Remove hpet vclock support

On Sat, Feb 1, 2014 at 7:43 AM, Clemens Ladisch <clemens@...isch.de> wrote:
> Andy Lutomirski wrote:
>> The HPET is so amazingly slow that this is barely a win.
>
> What happens on CPUs where the TSC cannot be used for the clock?

vclock_gettime, etc will fall back to using syscalls, just like they
would on systems using the PIT timer.

>
>> it scares me a tiny bit to map a piece of crappy hardware where every
>> userspace program can poke at it (even if said poking is read-only).
>> Let's just remove it.
>
> So this mapping is a backdoor to bypass the restrictions on /dev/hpet?  ;-)
>

Yes, except that it's read-only.

At some point, someone will probably want to run code in a sandbox
that can't tell time at all.  That will be messy, but this is a decent
first little step.

--Andy
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