Re: [PATCH 0/4] Avoid soft lockup message when KVM is stopped byhost

[Anthony Liguori]

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.

IIRC, the steal time patches have some logic that basically say:

if there was steal time:
   kick soft lockup detector

I wonder if that serves this purpose provided that time spent in stop is 
accounted as steal time.  If it isn't, perhaps it should be?

Regards,

Anthony Liguori

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