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

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Date:	Wed, 31 Oct 2012 09:01:01 +0000
From:	"Hatayama, Daisuke" <d.hatayama@...fujitsu.com>
To:	zhangyanfei <zhangyanfei@...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



> -----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.

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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