[PATCH v2 12/23] MIPS: KVM: Migrate hrtimer to follow VCPU

James Hogan
2014-05-29T09:17:06Z

When a VCPU is scheduled in on a different CPU, refresh the hrtimer used
for emulating count/compare so that it gets migrated to the same CPU.

This should prevent a timer interrupt occurring on a different CPU to
where the guest it relates to is running, which would cause the guest
timer interrupt not to be delivered until after the next guest exit.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: kvm@vger.kernel.org
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: Sanjay Lal <sanjayl@kymasys.com>
---
v2:
- Move kvm_mips_migrate_count() into kvm_tlb.c to fix a link error when
KVM is built as a module, since kvm_tlb.c is built statically and
cannot reference symbols in kvm_mips_emul.c.
---
arch/mips/kvm/kvm_tlb.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

diff --git a/arch/mips/kvm/kvm_tlb.c b/arch/mips/kvm/kvm_tlb.c
index 9d371ee0a755..d65999a9f8af 100644
--- a/arch/mips/kvm/kvm_tlb.c
+++ b/arch/mips/kvm/kvm_tlb.c
@@ -656,6 +656,23 @@ void kvm_local_flush_tlb_all(void)
local_irq_restore(flags);
}

+/**
+ * kvm_mips_migrate_count() - Migrate timer.
+ * @vcpu: Virtual CPU.
+ *
+ * Migrate CP0_Count hrtimer to the current CPU by cancelling and restarting it
+ * if it was running prior to being cancelled.
+ *
+ * Must be called when the VCPU is migrated to a different CPU to ensure that
+ * timer expiry during guest execution interrupts the guest and causes the
+ * interrupt to be delivered in a timely manner.
+ */
+static void kvm_mips_migrate_count(struct kvm_vcpu *vcpu)
+{
+ if (hrtimer_cancel(&vcpu->arch.comparecount_timer))
+ hrtimer_restart(&vcpu->arch.comparecount_timer);
+}
+
/* Restore ASID once we are scheduled back after preemption */
void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
{
@@ -691,6 +708,12 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
if (vcpu->arch.last_sched_cpu != cpu) {
kvm_info("[%d->%d]KVM VCPU[%d] switch\n",
vcpu->arch.last_sched_cpu, cpu, vcpu->vcpu_id);
+ /*
+ * Migrate the timer interrupt to the current CPU so that it
+ * always interrupts the guest and synchronously triggers a
+ * guest timer interrupt.
+ */
+ kvm_mips_migrate_count(vcpu);
}

if (!newasid) {
--
1.9.3