On Wed, May 05, 2010 at 05:46:59PM +0300, Avi Kivity wrote: > 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? I don't know. I traced the Xen crash down and found that is gets a #GP because it tries to set this bit. > Obviously it isn't needed since it manages to run on Intel without it. I have heard inofficial statements that they set this bit to provide the functionality to their guests. And Xen sets this bit together with the SVM bit. >> /* 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? It is present in all SVM capable AMD processors. > 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). Because there is no cpuid bit for this feature. You can roughly check for it using the svm cpuid bit. Joerg -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html