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

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

[Matthias Lange]

When running Linux as a guest with KVM on an AMD CPU, the guest Linux kernel
tries to read the MC4_MISC1 MSR from its MCE code. Because this MSR is not
virtualized within KVM a GPE is injected into the guest. This patch adds
support to virtualize the MC4_MSR.

Matthias Lange (1):
  KVM: svm: virtualize MSR reads from MC4_MISC1

 arch/x86/kvm/x86.c | 3 +++
 1 file changed, 3 insertions(+)

-- 
1.9.1

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

[Matthias Lange]

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);
-- 
1.9.1

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

[Paolo Bonzini]

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?

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.

Paolo

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

[Matthias Lange]

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.

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

[Paolo Bonzini]

Il 10/07/2014 11:31, Matthias Lange ha scritto:
> 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.
>

Can you please add the MSR name to a .h file instead, and handle it in 
get_msr_mce?

Paolo