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

Serge Belyshev
2010-08-16T13:49:44Z

Alexander Graf <agraf@suse.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.