linux-kernel - Re: [PATCH 4/5] KVM: SVM: Allow EFER.LMSLE to be set with nested svm

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Date:	Wed, 05 May 2010 17:46:59 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Joerg Roedel <joerg.roedel@....com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] KVM: SVM: Allow EFER.LMSLE to be set with nested
 svm

On 05/05/2010 05:04 PM, Joerg Roedel wrote:
> This patch enables setting of efer bit 13 which is allowed
> in all SVM capable processors. This is necessary for the
> SLES11 version of Xen 4.0 to boot with nested svm.
>    

Interesting, why does it require it?

Obviously it isn't needed since it manages to run on Intel without it.

>   /* Intel MSRs. Some also available on other CPUs */
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 74f7b9d..bc087c7 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -610,7 +610,7 @@ static __init int svm_hardware_setup(void)
>
>   	if (nested) {
>   		printk(KERN_INFO "kvm: Nested Virtualization enabled\n");
> -		kvm_enable_efer_bits(EFER_SVME);
> +		kvm_enable_efer_bits(EFER_SVME | EFER_LMSLE);
>   	}
>
>   	for_each_possible_cpu(cpu) {
>    

What if the host doesn't have it?

Why enable it only for the nested case?  It's not svm specific (it's 
useful for running non-hvm Xen in non-nested mode).

Isn't there a cpuid bit for it?  If so, it should be exposed to 
userspace, and the feature should depend on it.

-- 
error compiling committee.c: too many arguments to function

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