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    SubjectRe: [PATCH 0/4] Avoid soft lockup message when KVM is stopped by host
    On Tue, Aug 30, 2011 at 10:37:13AM -0600, Eric B Munson wrote:
    > On Tue, Aug 30, 2011 at 06:26, Marcelo Tosatti <mtosatti@redhat.com> 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?
    >
    > The hypervisor will set the flag (the second bit in the struct
    > pvclock_vcpu_time_info.flags field) when it stops the guest. I could
    > be reading pvclock-abi.h incorrectly, but the way I understand it is
    > that this structure is used to communicate between hypervisor and
    > guest.

    Yes, its awkward though (to have an interface to modify a bit in
    pvclock->flags from QEMU).

    Anyway, it appears that all elements to fix this in QEMU without the
    need for a paravirt interface are available... did you look into my
    suggestion?

    > > 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.
    > >
    --
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