[PATCH v4 1/2] KVM: PPC: Add new capability to control MCE behaviour

[Aravinda Prasad]

This patch introduces a new KVM capability to control
how KVM behaves on machine check exception (MCE).
Without this capability, KVM redirects machine check
exceptions to guest's 0x200 vector, if the address in
error belongs to the guest. With this capability KVM
causes a guest exit with NMI exit reason.

The new capability is required to avoid problems if
a new kernel/KVM is used with an old QEMU for guests
that don't issue "ibm,nmi-register". As old QEMU does
not understand the NMI exit type, it treats it as a
fatal error. However, the guest could have handled
the machine check error if the exception was delivered
to guest's 0x200 interrupt vector instead of NMI exit
in case of old QEMU.

QEMU part can be found at:
http://lists.nongnu.org/archive/html/qemu-ppc/2015-12/msg00199.html

Change Log v4:
  - Allow host-side handling of the machine check exception before
    passing on the exception to the guest.

Change Log v3:
  - Split the patch into 2. First patch introduces the
    new capability while the second one enhances KVM to
    redirect MCE.
  - Fix access width bug

Change Log v2:
  - Added KVM capability

Signed-off-by: Aravinda Prasad <aravinda at linux.vnet.ibm.com>
Reviewed-by: David Gibson <david at gibson.dropbear.id.au>
---
 arch/powerpc/include/asm/kvm_host.h |    1 +
 arch/powerpc/kernel/asm-offsets.c   |    1 +
 arch/powerpc/kvm/powerpc.c          |    7 +++++++
 include/uapi/linux/kvm.h            |    1 +
 4 files changed, 10 insertions(+)

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 28350a2..018c684 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -264,6 +264,7 @@ struct kvm_arch {
 	int hpt_cma_alloc;
 	struct dentry *debugfs_dir;
 	struct dentry *htab_dentry;
+	u8 fwnmi_enabled;
 #endif /* CONFIG_KVM_BOOK3S_HV_POSSIBLE */
 #ifdef CONFIG_KVM_BOOK3S_PR_POSSIBLE
 	struct mutex hpt_mutex;
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index caec7bf..3acd503 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -494,6 +494,7 @@ int main(void)
 	DEFINE(KVM_NEED_FLUSH, offsetof(struct kvm, arch.need_tlb_flush.bits));
 	DEFINE(KVM_ENABLED_HCALLS, offsetof(struct kvm, arch.enabled_hcalls));
 	DEFINE(KVM_VRMA_SLB_V, offsetof(struct kvm, arch.vrma_slb_v));
+	DEFINE(KVM_FWNMI, offsetof(struct kvm, arch.fwnmi_enabled));
 	DEFINE(VCPU_DSISR, offsetof(struct kvm_vcpu, arch.shregs.dsisr));
 	DEFINE(VCPU_DAR, offsetof(struct kvm_vcpu, arch.shregs.dar));
 	DEFINE(VCPU_VPA, offsetof(struct kvm_vcpu, arch.vpa.pinned_addr));
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 70963c8..a4405a8 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -604,6 +604,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		r = cpu_has_feature(CPU_FTR_TM_COMP) &&
 		    is_kvmppc_hv_enabled(kvm);
 		break;
+	case KVM_CAP_PPC_FWNMI:
+		r = 1;
+		break;
 	default:
 		r = 0;
 		break;
@@ -1204,6 +1207,10 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
 		break;
 	}
 #endif /* CONFIG_KVM_XICS */
+	case KVM_CAP_PPC_FWNMI:
+		r = 0;
+		vcpu->kvm->arch.fwnmi_enabled = true;
+		break;
 	default:
 		r = -EINVAL;
 		break;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 4ee67cb..3e41c42 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -870,6 +870,7 @@ struct kvm_ppc_smmu_info {
 #define KVM_CAP_S390_USER_INSTR0 130
 #define KVM_CAP_MSI_DEVID 131
 #define KVM_CAP_PPC_HTM 132
+#define KVM_CAP_PPC_FWNMI 133
 
 #ifdef KVM_CAP_IRQ_ROUTING