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

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Date:	Mon, 05 Mar 2012 09:10:02 -0800
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, 5 Mar 2012 13:39:43 -0300, 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.


Okay, that will go into V16 then...

Eric
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