[PATCH v6 1/2] KVM: PPC: Add new capability to control MCE behaviour

Mahesh J Salgaonkar mahesh at linux.vnet.ibm.com
Mon Feb 6 06:17:17 AEDT 2017

From: Aravinda Prasad <aravinda at linux.vnet.ibm.com>

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.

Signed-off-by: Aravinda Prasad <aravinda at linux.vnet.ibm.com>
Reviewed-by: David Gibson <david at gibson.dropbear.id.au>
Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
 Documentation/virtual/kvm/api.txt   |   11 +++++++++++
 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 +
 5 files changed, 21 insertions(+)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 03145b7..e2960e0 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3914,6 +3914,17 @@ to take care of that.
 This capability can be enabled dynamically even if VCPUs were already
 created and are running.
+Architectures: ppc
+Parameters: none
+With this capability a machine check exception in the guest address
+space will cause KVM to exit the guest with NMI exit reason. This
+enables QEMU to build error log and branch to guest kernel registered
+machine check handling routine. Without this capability KVM will
+branch to guests' 0x200 interrupt vector.
 8. Other capabilities.
diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index e59b172..5f031a7 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -266,6 +266,7 @@ struct kvm_arch {
 	int hpt_cma_alloc;
 	struct dentry *debugfs_dir;
 	struct dentry *htab_dentry;
+	u8 fwnmi_enabled;
 	struct mutex hpt_mutex;
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 0601e6a..df29caf 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -498,6 +498,7 @@ 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 cd892de..14377bb 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -610,6 +610,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		r = cpu_has_feature(CPU_FTR_TM_COMP) &&
+		r = 1;
+		break;
 		r = 0;
@@ -1210,6 +1213,10 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
 #endif /* CONFIG_KVM_XICS */
+		r = 0;
+		vcpu->kvm->arch.fwnmi_enabled = true;
+		break;
 		r = -EINVAL;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index cac48ed..4783d11 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -871,6 +871,7 @@ 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

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