Re: [PATCH] KVM: svm: virtualize MSR reads from MC4_MISC1

[Matthias Lange <matthias.lange@kernkonzept.com>]

On Wed, Jul 09, 2014 at 06:26:23PM +0200, Paolo Bonzini wrote:
> Il 26/06/2014 14:22, Matthias Lange ha scritto:
> >Linux' AMD MCE code tries to read from the MC4_MISC1 (0xc0000408) MSR. Because
> >this read is not virtualized within KVM, a GPE is injected into the guest.
> >This patch handles guest reads from MC4_MISC and returns 0 to the guest.
> >
> >Signed-off-by: Matthias Lange <matthias.lange@kernkonzept.com>
> >---
> > arch/x86/kvm/x86.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> >diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >index 24d70d4..d5a305b 100644
> >--- a/arch/x86/kvm/x86.c
> >+++ b/arch/x86/kvm/x86.c
> >@@ -2530,6 +2530,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
> > 			return 1;
> > 		data = vcpu->arch.osvw.status;
> > 		break;
> >+	case 0xc0000408: /* MC4_MISC1 */
> >+		data = 0;
> >+		break;
> > 	default:
> > 		if (kvm_pmu_msr(vcpu, msr))
> > 			return kvm_pmu_get_msr(vcpu, msr, pdata);
> >
> 
> Why don't you have to do the same with MC4_MISC0?

MC4_MISC0 (0x413) is handled in kvm_get_msr_common by this statement

  case MSR_IA32_MC0_CTL ... MSR_IA32_MC0_CTL + 4 * KVM_MAX_MCE_BANKS - 1:
          return get_msr_mce(vcpu, msr, pdata);

and get_msr_mce returns a sane value from the vcpu mce_banks.

> Is your kernel compiled with or without CONFIG_PARAVIRT?  Paravirt does
> 
>         .read_msr = native_read_msr_safe,
>         .write_msr = native_write_msr_safe,
> 
> so you shouldn't get these #GP exceptions.

I used the default i386_defconfig to build the guest kernel. CONFIG_PARAVIRT
is disabled in this setup.

Matthias.