linux-kernel - Re: [PATCH v2] clocksource/arm_arch_timer: Fix masking for high freq counters

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]

Date:   Sun, 8 Aug 2021 12:01:10 -0700
From:   Oliver Upton <oupton@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Shier <pshier@...gle.com>,
        Raghavendra Rao Ananta <rananta@...gle.com>,
        Ricardo Koller <ricarkol@...gle.com>
Subject: Re: [PATCH v2] clocksource/arm_arch_timer: Fix masking for high freq counters

On Sun, Aug 8, 2021 at 3:40 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On Sun, 08 Aug 2021 02:14:35 +0100,
> Oliver Upton <oupton@...gle.com> wrote:
>
> > The only other sane idea that I could come up with is providing this
> > information to the kernel through DT, although that would leave ACPI
> > systems behind.
>
> It also has the disadvantage that a large number of DT timer nodes are
> a mess of cargo-culted, copy-pasted idioms, and that adding another
> property would only make it worse.

Agreed, this does seem like the best solution, short of the
architecture actually providing something to determine the counter
width.

On that note, I wonder how (if ever) we will be able to move away from
unnecessarily masking a 64 bit counter, i.e. a v8.6 or above
implementation. With this patch, one such counter would wrap after
36.56 years, short of the 40 year guarantee we have from the
architecture for < v8.6 implementations. Getting it to 64 bits would
squarely make it someone else's problem ~585 years from now :)

--
Thanks,
Oliver