linux-kernel - Re: [PATCH 0/4] Avoid soft lockup message when KVM is stopped by host

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Message-ID: <20110830122630.GA19450@amt.cnet>
Date:	Tue, 30 Aug 2011 09:26:30 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Eric B Munson <emunson@...bm.net>
Cc:	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
Subject: Re: [PATCH 0/4] Avoid soft lockup message when KVM is stopped by host

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.
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