[PATCH 10/21] MIPS: KVM: Migrate hrtimer to follow VCPU

James Hogan
2014-04-25T15:20:40Z

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>
---
arch/mips/include/asm/kvm_host.h | 1 +
arch/mips/kvm/kvm_mips_emul.c | 17 +++++++++++++++++
arch/mips/kvm/kvm_tlb.c | 6 ++++++
3 files changed, 24 insertions(+)

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index 90e1c0005ff4..f56bb699506e 100644
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -705,6 +705,7 @@ extern enum emulation_result kvm_mips_complete_mmio_load(struct kvm_vcpu *vcpu,
struct kvm_run *run);

enum emulation_result kvm_mips_emulate_count(struct kvm_vcpu *vcpu);
+void kvm_mips_migrate_count(struct kvm_vcpu *vcpu);

enum emulation_result kvm_mips_check_privilege(unsigned long cause,
uint32_t *opc,
diff --git a/arch/mips/kvm/kvm_mips_emul.c b/arch/mips/kvm/kvm_mips_emul.c
index bad31c6235d4..7be7317be45d 100644
--- a/arch/mips/kvm/kvm_mips_emul.c
+++ b/arch/mips/kvm/kvm_mips_emul.c
@@ -249,6 +249,23 @@ enum emulation_result kvm_mips_emulate_count(struct kvm_vcpu *vcpu)
return er;
}

+/**
+ * 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.
+ */
+void kvm_mips_migrate_count(struct kvm_vcpu *vcpu)
+{
+ if (hrtimer_cancel(&vcpu->arch.comparecount_timer))
+ hrtimer_restart(&vcpu->arch.comparecount_timer);
+}
+
enum emulation_result kvm_mips_emul_eret(struct kvm_vcpu *vcpu)
{
struct mips_coproc *cop0 = vcpu->arch.cop0;
diff --git a/arch/mips/kvm/kvm_tlb.c b/arch/mips/kvm/kvm_tlb.c
index 9d371ee0a755..1f61fe6739da 100644
--- a/arch/mips/kvm/kvm_tlb.c
+++ b/arch/mips/kvm/kvm_tlb.c
@@ -691,6 +691,12 @@ 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) {
--
1.8.1.2