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Date: Thu, 30 Jan 2014 10:03:16 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Andy Lutomirski <luto@amacapital.net>,
        Stefani Seibold <stefani@seibold.net>
CC: Greg KH <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        X86 ML <x86@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
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        Andrea Arcangeli <aarcange@redhat.com>,
        John Stultz <john.stultz@linaro.org>,
        Pavel Emelyanov <xemul@parallels.com>,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        andriy.shevchenko@linux.intel.com, Martin.Runge@rohde-schwarz.com,
        Andreas.Brief@rohde-schwarz.com
Subject: Re: [PATCH 0/4] Add 32 bit VDSO time function support
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On 01/30/2014 09:57 AM, Andy Lutomirski wrote:
> 
> By definition there aren't any broken users of the new functions,
> because there aren't any users at all.  So... should we start
> randomizing this thing from the beginning?
> 

The vdso already exists.  It isn't new.  Randomizing it might be a good
idea, though; it already is randomized on 64 bits.

> Also, since the VVAR page has a real vma, should something be done to
> prevent mprotect or ptrace from COWing it?  Users will be rather
> surprised if it suddenly stops updating.

What happens currently on 64 bits?  I think we just take the attitude
that "don't do that, then", and it hasn't seemed to be a problem.

> Finally, this might be the time to kill off the userspace mapping of
> the HPET.  I suspect that there are few if any machines for which the
> HPET is fast enough that avoiding a syscall matters at all.  (On my
> box at work, reading the HPET takes ~500 nanoseconds.  I can do a lot
> of syscalls in that amount of time.)

I think this can be independent of extending the current 64-bit
functionality to 32 bits.  It is a valid question, though.

	-hpa