linux-kernel - Re: [PATCH 23/42] KVM: Activate Virtualization On Demand

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Date:	Mon, 16 Aug 2010 13:49:39 +0000
From:	Serge Belyshev <belyshev@...ni.sinp.msu.ru>
To:	Alexander Graf <agraf@...e.de>
Cc:	Dieter Ries <mail@...terries.net>, Avi Kivity <avi@...hat.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 23/42] KVM: Activate Virtualization On Demand

Alexander Graf <agraf@...e.de> writes:

> Hrm - try to use the following (probably whitespace broken and 100% untested) hacky patch:
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 56c9b6b..bde9ee3 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -429,9 +429,11 @@ static int svm_hardware_enable(void *garbage)
>         struct desc_struct *gdt;
>         int me = raw_smp_processor_id();
>  
> +#if 0
>         rdmsrl(MSR_EFER, efer);
>         if (efer & EFER_SVME)
>                 return -EBUSY;
> +#endif
>  

I tested a bit different hack keeping rdmsrl but removing the if() and
it works fine for me:

Index: linux/arch/x86/kvm/svm.c
===================================================================
--- linux.orig/arch/x86/kvm/svm.c
+++ linux/arch/x86/kvm/svm.c
@@ -429,8 +429,7 @@ static int svm_hardware_enable(void *gar
 	int me = raw_smp_processor_id();
 
 	rdmsrl(MSR_EFER, efer);
-	if (efer & EFER_SVME)
-		return -EBUSY;
+	printk(KERN_DEBUG "svm_hardware_enable: efer %x on %d\n", efer, me);
 
 	if (!has_svm()) {
 		printk(KERN_ERR "svm_hardware_enable: err EOPNOTSUPP on %d\n",

Here is an example of its output:

[231441.358111] svm_hardware_enable: efer 1d01 on 0
[231441.358117] svm_hardware_enable: efer d01 on 3
[231441.358124] svm_hardware_enable: efer d01 on 2
[231441.358135] svm_hardware_enable: efer d01 on 1
[231675.168967] svm_hardware_enable: efer d01 on 0
[231675.168972] svm_hardware_enable: efer d01 on 1
[231675.168983] svm_hardware_enable: efer d01 on 2
[231675.168995] svm_hardware_enable: efer d01 on 3


After reboot, the first kvm run always reports efer = 1d01 on the first cpu.
In all subsequent runs before reboot efer stays d01 on all cpus.
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