linux-kernel - Re: [PATCH 0/4 V13] Avoid soft lockup message when KVM is stopped by host

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Date:	Sat, 10 Mar 2012 14:53:16 -0500
From:	Eric B Munson <emunson@...bm.net>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	avi@...hat.com, mingo@...hat.com, hpa@...or.com,
	ryanh@...ux.vnet.ibm.com, aliguori@...ibm.com, kvm@...r.kernel.org,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4 V13] Avoid soft lockup message when KVM is stopped by
 host

On Mon, 05 Mar 2012, Marcelo Tosatti wrote:

> On Tue, Feb 14, 2012 at 04:17:20PM -0500, Eric B Munson wrote:
> > On Tue, 14 Feb 2012, Marcelo Tosatti wrote:
> > 
> > > On Tue, Feb 14, 2012 at 10:50:13AM -0500, Eric B Munson wrote:
> > > > On Tue, 14 Feb 2012, Marcelo Tosatti wrote:
> > > > 
> > > > > On Tue, Feb 14, 2012 at 10:29:31AM -0500, Eric B Munson wrote:
> > > > > > On Wed, 08 Feb 2012, Eric B Munson wrote:
> > > > > > 
> > > > > > > 
> > > > > > > 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.
> > > > > > 
> > > > > > Avi,
> > > > > > 
> > > > > > Is this set fit for merging or is there something else you want changed?
> > > > > 
> > > > > Eric,
> > > > > 
> > > > > On Message-ID: <20120210160536.GA23363@....cnet>, i asked:
> > > > > 
> > > > > How is the stub getting included for other architectures again?
> > > > > 
> > > > 
> > > > Marcelo,
> > > > 
> > > > Sorry, I put out V13 to answer that.  There is a stub in asm-generic that was
> > > > lost in the V11-V12 rebase.  This stub has be included in the V13 set.
> > > > 
> > > > Eric
> > > 
> > > Eric, 
> > > 
> > > I know the stub has been included in the series. But i am asking how 
> > > it is #include'ed for other architectures? (can't see that).
> > 
> > Marcelo,
> > 
> > kernel/watchdog.c now includes linux/kvm_para.h which includes asm/kvm_para.h.
> > The check_and_clear function is defined in arch include/asm/kvm_para.h or in
> > asm-generic/kvm_para.h for any arch lacking the specific header in their asm
> > include dir.  If I have misunderstood how these headers work, please let me
> > know and I will fix it.
> 
> There is no automatic inclusion of asm-generic/ headers. You must create
> kvm_para.h in each architecture's include/asm/ directory, #including
> asm-generic/kvm_para.h.
> 

Hopefully V16 handles this properly, please let me know if there is anything
that needs to be addressed.  I'd like to see this set in for the 3.4 window.

Eric

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