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

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Date:	Thu, 01 Nov 2012 13:55:04 +0800
From:	zhangyanfei <zhangyanfei@...fujitsu.com>
To:	"Hatayama, Daisuke" <d.hatayama@...fujitsu.com>
CC:	"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>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH v3 2/2] KVM: make crash_clear_loaded_vmcss valid when
 loading kvm_intel module

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.

Thanks
Zhang Yanfei

> What does happen if calling vmclear_local_loaded_vmcss before kvm_init? I think it no problem since the list is initially empty.
> 
>>  	vmx_disable_intercept_for_msr(MSR_FS_BASE, false);
>>  	vmx_disable_intercept_for_msr(MSR_GS_BASE, false);
>>  	vmx_disable_intercept_for_msr(MSR_KERNEL_GS_BASE, true);
>> @@ -7265,6 +7270,10 @@ static void __exit vmx_exit(void)
>>  	free_page((unsigned long)vmx_io_bitmap_b);
>>  	free_page((unsigned long)vmx_io_bitmap_a);
>>
>> +#ifdef CONFIG_KEXEC
>> +	crash_clear_loaded_vmcss = NULL;
>> +#endif
>> +
>>  	kvm_exit();
>>  }
> 
> Also, this is converse to the above.
> 
> Thanks.
> HATAYAMA, Daisuke
> 
> 

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