Re: soft lockup when passing vvar address to write(2)

From	Ingo Molnar <mingo@kernel.org>
Newsgroups	linux.kernel
Subject	Re: soft lockup when passing vvar address to write(2)
Date	2016-03-05 10:10 +0100
Message-ID	<r9gnM-3TX-21@gated-at.bofh.it> (permalink)
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* Thomas Gleixner <tglx@linutronix.de> wrote:

> On Fri, 4 Mar 2016, Andy Lutomirski wrote:
> > Thomas, I still think we should consider just deleting the HPET vclock
> > code and accept the syscall overhead on systems that are stuck using
> > HPET.  If fast syscalls are available (which should include every
> > system with HPET, unless there are some 32-bit AMD systems lying
> > around), then the overhead in a syscall is *tiny* compared to the code
> > of the HPET read itself.
> 
> No objection from my side, really.

Seconded. HPET hardware overhead is typically horrifically large in any case, no 
need to memory map it and expose hardware breakages to user-space ...

It's also a (mild) security hole: a well-known HPET address can be abused as a 
statistical trampoline periodically cycling through 'dangerous' instruction 
values.

Thanks,

	Ingo

Thread

Re: soft lockup when passing vvar address to write(2) Andy Lutomirski <luto@amacapital.net> - 2016-03-05 00:50 +0100
  Re: soft lockup when passing vvar address to write(2) Thomas Gleixner <tglx@linutronix.de> - 2016-03-05 09:30 +0100
    Re: soft lockup when passing vvar address to write(2) Ingo Molnar <mingo@kernel.org> - 2016-03-05 10:10 +0100
      Re: soft lockup when passing vvar address to write(2) Andy Lutomirski <luto@amacapital.net> - 2016-03-06 04:00 +0100

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