KVM: PPC: Book3S HV: Exit guest upon MCE when FWNMI capability is enabled

Enhance KVM to cause a guest exit with KVM_EXIT_NMI
exit reason upon a machine check exception (MCE) in
the guest address space if the KVM_CAP_PPC_FWNMI
capability is enabled (instead of delivering a 0x200
interrupt to guest). This enables QEMU to build error
log and deliver machine check exception to guest via
guest registered machine check handler.

This approach simplifies the delivery of machine
check exception to guest OS compared to the earlier
approach of KVM directly invoking 0x200 guest interrupt
vector.

This design/approach is based on the feedback for the
QEMU patches to handle machine check exception. Details
of earlier approach of handling machine check exception
in QEMU and related discussions can be found at:

https://lists.nongnu.org/archive/html/qemu-devel/2014-11/msg00813.html

Note:

This patch now directly invokes machine_check_print_event_info()
from kvmppc_handle_exit_hv() to print the event to host console
at the time of guest exit before the exception is passed on to the
guest. Hence, the host-side handling which was performed earlier
via machine_check_fwnmi is removed.

The reasons for this approach is (i) it is not possible
to distinguish whether the exception occurred in the
guest or the host from the pt_regs passed on the
machine_check_exception(). Hence machine_check_exception()
calls panic, instead of passing on the exception to
the guest, if the machine check exception is not
recoverable. (ii) the approach introduced in this
patch gives opportunity to the host kernel to perform
actions in virtual mode before passing on the exception
to the guest. This approach does not require complex
tweaks to machine_check_fwnmi and friends.

Signed-off-by: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

1 files changed, 17 insertions, 1 deletions

diff --git a/arch/powerpc/kvm/book3s_hv_ras.c b/arch/powerpc/kvm/book3s_hv_ras.c
index 7ef0993214f3..c356f9a40b24 100644
--- a/arch/powerpc/kvm/book3s_hv_ras.c
+++ b/arch/powerpc/kvm/book3s_hv_ras.c
@@ -130,12 +130,28 @@ static long kvmppc_realmode_mc_power7(struct kvm_vcpu *vcpu)
 
 out:
 	/*
+	 * For guest that supports FWNMI capability, hook the MCE event into
+	 * vcpu structure. We are going to exit the guest with KVM_EXIT_NMI
+	 * exit reason. On our way to exit we will pull this event from vcpu
+	 * structure and print it from thread 0 of the core/subcore.
+	 *
+	 * For guest that does not support FWNMI capability (old QEMU):
 	 * We are now going enter guest either through machine check
 	 * interrupt (for unhandled errors) or will continue from
 	 * current HSRR0 (for handled errors) in guest. Hence
 	 * queue up the event so that we can log it from host console later.
 	 */
-	machine_check_queue_event();
+	if (vcpu->kvm->arch.fwnmi_enabled) {
+		/*
+		 * Hook up the mce event on to vcpu structure.
+		 * First clear the old event.
+		 */
+		memset(&vcpu->arch.mce_evt, 0, sizeof(vcpu->arch.mce_evt));
+		if (get_mce_event(&mce_evt, MCE_EVENT_RELEASE)) {
+			vcpu->arch.mce_evt = mce_evt;
+		}
+	} else
+		machine_check_queue_event();
 
 	return handled;
 }