linux-kernel - Re: [PATCH 0/5 V4] Avoid soft lockup message when KVM is stopped by host

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Message-ID: <20111201212558.GC25290@amt.cnet>
Date:	Thu, 1 Dec 2011 19:25:58 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Eric B Munson <emunson@...bm.net>
Cc:	avi@...hat.com, mingo@...hat.com, hpa@...or.com, arnd@...db.de,
	ryanh@...ux.vnet.ibm.com, aliguori@...ibm.com,
	jeremy.fitzhardinge@...rix.com, kvm@...r.kernel.org,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5 V4]  Avoid soft lockup message when KVM is stopped by
 host

On Tue, Nov 29, 2011 at 04:35:34PM -0500, Eric B Munson wrote:
> Changes from V3:
> Include CC's on patch 3
> Drop clear flag ioctl and have the watchdog clear the flag when it is reset
> 
> Changes from V2:
> A new kvm functions defined in kvm_para.h, the only change to pvclock is the
> initial flag definition
> 
> Changes from V1:
> (Thanks Marcelo)
> Host code has all been moved to arch/x86/kvm/x86.c
> KVM_PAUSE_GUEST was renamed to KVM_GUEST_PAUSED
> 
> When a guest kernel is stopped by the host hypervisor it can look like a soft
> lockup to the guest kernel.  This false warning can mask later soft lockup
> warnings which may be real.  This patch series adds a method for a host
> hypervisor to communicate to a guest kernel that it is being stopped.  The
> final patch in the series has the watchdog check this flag when it goes to
> issue a soft lockup warning and skip the warning if the guest knows it was
> stopped.
> 
> It was attempted to solve this in Qemu, but the side effects of saving and
> restoring the clock and tsc for each vcpu put the wall clock of the guest behind
> by the amount of time of the pause.  This forces a guest to have ntp running
> in order to keep the wall clock accurate.

Looks good to me.

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