Hi, here is a small patch-set to fix a race condition which happens when an RTC-IRQ is migrated to another VCPU while it is being handled by the guest. The RTC-EOI handling in KVM requires that all sent interrupt messages to the VCPUs need to be acked before another RTC-IRQ can be sent. When an EOI signal from the guest is lost, it will never see an RTC interrupt again (until it reboots). This is easily reproducible with a Linux guest executing this loop: $ while true;do time hwclock --show --test --debug;done When the guest has multiple vcpus and the RTC-IRQ is regularily migrated (e.g. by irqbalance), the race condition will be hit after some time and the hwclock tool will fail with: select() to /dev/rtc to wait for clock tick timed out...synchronization failed The race condition happens because of the way the EOI backtracking between local APIC and IOAPIC works in KVM. The destination VCPU and vector is part of the IOAPIC state. When the guest sends an EOI to the local APIC the vector is matched against the destinations stored in the IOAPIC and ACKed there too if it matches. The problem begins when a VCPU handles an RTC interrupt and at the same time another VCPU migrates the RTC-IRQ away from that VCPU. This updates the IOAPIC state in KVM to the new destination, so that the EOI sent from the first VCPU does not match anymore in the IOAPIC, hence losing the RTC-EOI. This patch-set fixes the race-condition by adding explicit back-tracking information for RTC-IRQs. The rtc_status struct already holds a dest_map bitmap to store which VCPUs receveived an RTC-IRQ. This is extended to also hold the vector that was sent to this VCPU. This information is then used to match EOI signals from the guest to the RTC. This explicit back-tracking fixes the issue. Regards, Joerg Joerg Roedel (3): kvm: x86: Convert ioapic->rtc_status.dest_map to a struct kvm: x86: Track irq vectors in ioapic->rtc_status.dest_map kvm: x86: Check dest_map->vector to match eoi signals for rtc arch/x86/kvm/ioapic.c | 30 +++++++++++++++++++++--------- arch/x86/kvm/ioapic.h | 17 +++++++++++++++-- arch/x86/kvm/irq_comm.c | 2 +- arch/x86/kvm/lapic.c | 14 ++++++++------ arch/x86/kvm/lapic.h | 7 +++++-- 5 files changed, 50 insertions(+), 20 deletions(-) -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
