linux-kernel - Re: [PATCH 0/4] 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]

Message-ID: <20110913204955.GD9096@mgebm.net>
Date:	Tue, 13 Sep 2011 16:49:55 -0400
From:	Eric B Munson <emunson@...bm.net>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	Anthony Liguori <anthony@...emonkey.ws>, avi@...hat.com,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, arnd@...db.de,
	riel@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, kvm-ppc@...r.kernel.org,
	aliguori@...ibm.com, raharper@...ibm.com, kvm-ia64@...r.kernel.org,
	Glauber Costa <glommer@...il.com>, mjwolf@...ibm.com
Subject: Re: [PATCH 0/4] Avoid soft lockup message when KVM is stopped by host

On Fri, 09 Sep 2011, Marcelo Tosatti wrote:

> On Thu, Sep 01, 2011 at 02:27:49PM -0600, emunson@...bm.net wrote:
> > On Thu, 01 Sep 2011 14:24:12 -0500, Anthony Liguori wrote:
> > >On 08/30/2011 07:26 AM, Marcelo Tosatti wrote:
> > >>On Mon, Aug 29, 2011 at 05:27:11PM -0600, Eric B Munson wrote:
> > >>>Currently, when qemu stops a guest kernel that guest will
> > >>>issue a soft lockup
> > >>>message when it resumes.  This set provides the ability for
> > >>>qemu to comminucate
> > >>>to the guest that it has been stopped.  When the guest hits
> > >>>the watchdog on
> > >>>resume it will check if it was suspended before issuing the
> > >>>warning.
> > >>>
> > >>>Eric B Munson (4):
> > >>>   Add flag to indicate that a vm was stopped by the host
> > >>>   Add functions to check if the host has stopped the vm
> > >>>   Add generic stubs for kvm stop check functions
> > >>>   Add check for suspended vm in softlockup detector
> > >>>
> > >>>  arch/x86/include/asm/pvclock-abi.h |    1 +
> > >>>  arch/x86/include/asm/pvclock.h     |    2 ++
> > >>>  arch/x86/kernel/kvmclock.c         |   14 ++++++++++++++
> > >>>  include/asm-generic/pvclock.h      |   14 ++++++++++++++
> > >>>  kernel/watchdog.c                  |   12 ++++++++++++
> > >>>  5 files changed, 43 insertions(+), 0 deletions(-)
> > >>>  create mode 100644 include/asm-generic/pvclock.h
> > >>>
> > >>>--
> > >>>1.7.4.1
> > >>
> > >>How is the host supposed to set this flag?
> > >>
> > >>As mentioned previously, if you save save/restore the offset
> > >>added to
> > >>kvmclock on stop/cont (and the TSC MSR, forgot to mention that), no
> > >>paravirt infrastructure is required. Which means the issue is
> > >>also fixed
> > >>for older guests.
> > >

Marcelo,

I think that stopping the TSC is the wrong approach because it will break time
between the two systems so timething that expects the monotonic clock to move
consistently will be wrong.  IMO, messing with the TSC at run time to avoid a
watchdog message is the wrong solution, better to teach the watchdog to ignore
this special case.

Thanks,
Eric

Download attachment "signature.asc" of type "application/pgp-signature" (491 bytes)