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    SubjectRe: [PATCH 0/4] Avoid soft lockup message when KVM is stopped by host
     On Tue, 30 Aug 2011 15:36:13 -0300, Marcelo Tosatti wrote:
    > 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?

    I have not yet, but will look into it. I sent these out because I was
    under the impression that there was some discussion at LinuxCon about
    your suggestion and that it was agreed that the all user space solution
    was not feasible.

    >
    >> > 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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