linux-kernel - Re: infinite loop in read_hpet from ktime_get_boot_fast

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHmME9pOWk_ZteUZc_PT19rMn1kfYcXtmLcyAy5sncdV1tNuiQ@mail.gmail.com>
Date:   Thu, 13 Jun 2019 17:18:50 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Clemens Ladisch <clemens@...isch.de>,
        Sultan Alsawaf <sultan@...neltoast.com>,
        Waiman Long <longman@...hat.com>, X86 ML <x86@...nel.org>
Subject: Re: infinite loop in read_hpet from ktime_get_boot_fast_ns

Hey Arnd, Peter,

On Wed, Jun 12, 2019 at 4:01 PM Arnd Bergmann <arnd@...db.de> wrote:
> Documentation/core-api/timekeeping.rst describes the timekeeping
> interfaces. I think what you want here is ktime_get_coarse_boottime().
>
> Note that "coarse" means "don't access the hardware clocksource"
> here, which is faster than "fast", but less accurate.
>
> This is updated as often as "jiffies_64", but is in nanosecond resolution
> and takes suspended time into account.

Oh, thanks. Indeed ktime_get_coarse_boottime seems even better. It's
perhaps a bit slower, in that it has that seqlock, but that might give
better synchronization between CPUs as well.

Peter - any immediate downside you can think of compared to local_clock()?

Jason