linux-kernel - Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy

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: <20160225123429.GD5757@andariel.pipo.sk>
Date:	Thu, 25 Feb 2016 13:34:29 +0100
From:	Peter Krempa <pkrempa@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, Yuki Shibuya <shibuya.yk@...s.nec.co.jp>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy

On Fri, Feb 19, 2016 at 15:44:23 +0100, Radim Krčmář wrote:
> [Cc'd Peter, the last guy that touched timers in libvirt, because he
>  might know what tick policies are supposed to be.]

I found the following RFC that describes the design of timer access in
libvirt:

http://www.redhat.com/archives/libvir-list/2010-March/msg00304.html

> 
> 2016-02-18 18:55+0100, Paolo Bonzini:
> > On 18/02/2016 18:33, Paolo Bonzini wrote:
> >> On 18/02/2016 17:56, Radim Krčmář wrote:
> >>> 2016-02-18 17:13+0100, Paolo Bonzini:
> >>>> On 17/02/2016 20:14, Radim Krčmář wrote:
> >>>>> Discard policy uses ack_notifiers to prevent injection of PIT interrupts
> >>>>> before EOI from the last one.
> >>>>>
> >>>>> This patch changes the policy to always try to deliver the interrupt,
> >>>>> which makes a difference when its vector is in ISR.
> >>>>> Old implementation would drop the interrupt, but proposed one injects to
> >>>>> IRR, like real hardware would.
> >>>>
> >>>> This seems like what libvirt calls the "merge" policy:
> >>>
> >>> Oops, I never looked beyond QEMU after seeing that the naming in libvirt
> >>> doesn't even match ...
> >>>
> >>> I think the policy that KVM implements (which I call discard) is "delay"
> >>> in libvirt.  (https://libvirt.org/formatdomain.html#elementsTime)
> 
> (I looked at libvirt code, but couldn't find any use of merge or discard
>  policies, so please bear with me as I disagree wherever it's possible.)

Indeed, it looks like it never was implemented. Unfortunately i'm not
able to assist more in this case.

Peter

Download attachment "signature.asc" of type "application/pgp-signature" (820 bytes)