linux-kernel - Re: [RFC PATCH 0/2] Introduce a way to adjust CLOCK

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: <d9127c33-e067-9b49-5985-0b09e3ede279@amazon.com>
Date:   Wed, 10 Feb 2021 12:17:37 +0100
From:   Alexander Graf <graf@...zon.com>
To:     Hikaru Nishida <hikalium@...omium.org>,
        <linux-kernel@...r.kernel.org>
CC:     <suleiman@...gle.com>, Andra Paraschiv <andraprs@...zon.com>,
        "Arnd Bergmann" <arnd@...db.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        KVM list <kvm@...r.kernel.org>, <mtosatti@...hat.com>
Subject: Re: [RFC PATCH 0/2] Introduce a way to adjust CLOCK_BOOTTIME from
 userspace for VM guests



On 10.02.21 11:39, Hikaru Nishida wrote:
> 
> From: Hikaru Nishida <hikalium@...omium.org>
> 
> 
> Hi folks,
> 
> We'd like to add a sysfs interface that enable us to advance
> CLOCK_BOOTTIME from userspace. The use case of this change is that
> adjusting guest's CLOCK_BOOTTIME as host suspends to ensure that the
> guest can notice the device has been suspended.
> We have an application that rely on the difference between
> CLOCK_BOOTTIME and CLOCK_MONOTONIC to detect whether the device went
> suspend or not. However, the logic did not work well on VM environment
> since most VMs are pausing the VM guests instead of actually suspending
> them on the host's suspension.
> With following patches, we can adjust CLOCK_BOOTTIME without actually
> suspending guest and make the app working as intended.
> I think this feature is also useful for other VM solutions since there
> was no way to do this from userspace.
> 
> As far as I checked, it is working as expected but is there any concern
> about this change? If so, please let me know.

I don't fully grasp why you want the guest to manually adjust its 
CLOCK_BOOTTIME. Wouldn't it make more sense to extend kvmclock's notion 
of wall clock time to tell you about suspended vs executed wall clock?


Alex




Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879