linux-kernel - Re: [PATCH] Guest stop notification

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Message-ID: <4ED7BB11.1050309@siemens.com>
Date:	Thu, 01 Dec 2011 18:36:17 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Eric B Munson <emunson@...bm.net>
CC:	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"ryanh@...ux.vnet.ibm.com" <ryanh@...ux.vnet.ibm.com>,
	"aliguori@...ibm.com" <aliguori@...ibm.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"mtosatti@...hat.com" <mtosatti@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"avi@...hat.com" <avi@...hat.com>
Subject: Re: [PATCH] Guest stop notification

On 2011-12-01 18:22, Eric B Munson wrote:
> On Thu, 01 Dec 2011, Jan Kiszka wrote:
> 
>> On 2011-11-29 22:36, Eric B Munson wrote:
>>> Often when a guest is stopped from the qemu console, it will report spurious
>>> soft lockup warnings on resume.  There are kernel patches being discussed that
>>> will give the host the ability to tell the guest that it is being stopped and
>>> should ignore the soft lockup warning that generates.
>>>
>>> Signed-off-by: Eric B Munson <emunson@...bm.net>
>>> Cc: ryanh@...ux.vnet.ibm.com
>>> Cc: aliguori@...ibm.com
>>> Cc: mtosatti@...hat.com
>>> Cc: avi@...hat.com
>>> Cc: kvm@...r.kernel.org
>>> Cc: linux-kernel@...r.kernel.org
>>> ---
>>>  target-i386/kvm.c |    6 ++++++
>>>  1 files changed, 6 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
>>> index 5bfc21f..defd364 100644
>>> --- a/target-i386/kvm.c
>>> +++ b/target-i386/kvm.c
>>> @@ -336,12 +336,18 @@ static int kvm_inject_mce_oldstyle(CPUState *env)
>>>      return 0;
>>>  }
>>>  
>>> +static void kvm_put_guest_paused(CPUState *penv)
>>> +{
>>> +    kvm_vcpu_ioctl(penv, KVM_GUEST_PAUSED, 0);
>>> +}
>>
>> I see no need in encapsulating this in a separate function.
>>
>>> +
>>>  static void cpu_update_state(void *opaque, int running, RunState state)
>>>  {
>>>      CPUState *env = opaque;
>>>  
>>>      if (running) {
>>>          env->tsc_valid = false;
>>> +	kvm_put_guest_paused(env);
>>
>> checkpatch.pl would have asked you to remove this tab.
>>
>> More general:
>>
>> Why is this x86-only? If the kernel interface is x86-only, what prevents
>> making it generic right from the beginning?
> 
> Sorry, missed this question on the first pass, this is x86 only because the
> flag used lives in the pvclock structure.  AFAICT, there aren't any other
> architectures out there that implement paravirtualized clocks yet.

That's an implementation "detail" of the kernel. The interface (IOCTL or
kvm_run field) is generic, no?

I would just fire this notification from generic code, evaluate the
error (that was lacking so far), and only report it if it's something
else than "not supported".

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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