linux-kernel - Re: [PATCH v3 2/2] KVM: make crash_clear_loaded_vmcss valid when loading kvm

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Message-ID: <50A360C7.2070904@cn.fujitsu.com>
Date:	Wed, 14 Nov 2012 17:13:43 +0800
From:	zhangyanfei <zhangyanfei@...fujitsu.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	"Hatayama, Daisuke" <d.hatayama@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH v3 2/2] KVM: make crash_clear_loaded_vmcss valid when
 loading kvm_intel module

于 2012年11月14日 05:22, Marcelo Tosatti 写道:
> On Thu, Nov 01, 2012 at 01:55:04PM +0800, zhangyanfei wrote:
>> 于 2012年10月31日 17:01, Hatayama, Daisuke 写道:
>>>
>>>
>>>> -----Original Message-----
>>>> From: kexec-bounces@...ts.infradead.org
>>>> [mailto:kexec-bounces@...ts.infradead.org] On Behalf Of zhangyanfei
>>>> Sent: Wednesday, October 31, 2012 12:34 PM
>>>> To: x86@...nel.org; kexec@...ts.infradead.org; Avi Kivity; Marcelo
>>>> Tosatti
>>>> Cc: linux-kernel@...r.kernel.org; kvm@...r.kernel.org
>>>> Subject: [PATCH v3 2/2] KVM: make crash_clear_loaded_vmcss valid when
>>>> loading kvm_intel module
>>>>
>>>> Signed-off-by: Zhang Yanfei <zhangyanfei@...fujitsu.com>
>>>
>>> [...]
>>>
>>>> @@ -7230,6 +7231,10 @@ static int __init vmx_init(void)
>>>>  	if (r)
>>>>  		goto out3;
>>>>
>>>> +#ifdef CONFIG_KEXEC
>>>> +	crash_clear_loaded_vmcss = vmclear_local_loaded_vmcss;
>>>> +#endif
>>>> +
>>>
>>> Assignment here cannot cover the case where NMI is initiated after VMX is on in kvm_init and before vmclear_local_loaded_vmcss is assigned, though rare but can happen.
>>>
>>
>> By saying "VMX is on in kvm init", you mean kvm_init enables the VMX feature in the logical processor?
>> No, only there is a vcpu to be created, kvm will enable the VMX feature.
>>
>> I think there is no difference with this assignment before or after kvm_init because the vmcs linked
>> list must be empty before vmx_init is finished.
> 
> The list is not initialized before hardware_enable(), though. Should
> move the assignment after that.
> 
> Also, it is possible that the loaded_vmcss_on_cpu list is being modified
> _while_ crash executes say via NMI, correct? If that is the case, better
> flag that the list is under manipulation so the vmclear can be skipped.
> 

Thanks for your comments.
In the new patchset, I didn't move the crash_clear_loaded_vmcss assignment.
I added a new percpu variable vmclear_skipped to indicate everything:
1. Before the loaded_vmcss_on_cpu list is initialized, vmclear_skipped is 1 and
   this means if the machine crashes and doing kdump, crash_clear_loaded_vmcss
   still will not be called.
2. If the loaded_vmcss_on_cpu list is under manipulation, vmclear_skipped is
   set to 1 and after the manipulation is finished, the variable is set to 0.
3. After all loaded vmcss are vmcleared, vmclear_skipped is set to 1. So we
   needn't repeat to vmclear loaded vmcss in kdump path.

Please refer to the new version of the patchset I sent. If you have any suggestions, that'll be helpful.

Thanks
Zhang

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