linux-kernel - Re: [PATCH 0/5 V5] Avoid soft lockup message when KVM is stopped by host

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:	Mon, 19 Dec 2011 15:50:47 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Eric B Munson <emunson@...bm.net>, mingo@...hat.com, hpa@...or.com,
	arnd@...db.de, ryanh@...ux.vnet.ibm.com, aliguori@...ibm.com,
	jeremy.fitzhardinge@...rix.com, levinsasha928@...il.com,
	Jan Kiszka <jan.kiszka@...mens.com>, kvm@...r.kernel.org,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5 V5] Avoid soft lockup message when KVM is stopped by
 host

On Mon, Dec 19, 2011 at 02:11:08PM -0200, Marcelo Tosatti wrote:
> On Mon, Dec 19, 2011 at 02:59:10PM +0200, Avi Kivity wrote:
> > On 12/16/2011 11:31 AM, Marcelo Tosatti wrote:
> > > > >
> > > > > Slow enough that progress of the watchdog thread is unable to keep up
> > > > > with timer interrupt processing. This is considered a hang and
> > > > > should be reported.
> > > > 
> > > > It's not a guest hang though!
> > >
> > > No, but your host system is in such a load state that for the sake of
> > > system usability you better print out a warning message.
> > 
> > What's the point in printing it in the guest?  The guest can't observe
> > host conditions.
> >
> > > I don't see the advantage of preempt notifiers over the simple, paravirt
> > > solution proposed? Note kvmclock is already paravirt.
> > 
> > Right.
> > 
> > > What do you want to be done in preempt notifiers? Measure what to
> > > consider setting this flag?
> > 
> > Preemption while TASK_RUNNING or TASK_UNINTERRUPTIBLE.
> 
> Maybe it is good (not sure), need to look into schedstats and think of
> cases that would break legitimate guest hangs. And it probably also
> affects the position of clearing the flag on the guest side as its 
> currently done in Eric's patchset.

Is the task going to be TASK_UNINTERRUPTIBLE with SIGSTOP? Don't think
so. 

Note "Preemption while TASK_RUNNING or TASK_UNINTERRUPTIBLE" is not
functional for guest-paused-via-QEMU-monitor case.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/