[PATCH 27/45] KVM: x86: Optimize NMI watchdog delivery

Avi Kivity
2008-12-08T11:47:38Z

From: Jan Kiszka <jan.kiszka@siemens.com>

As suggested by Avi, this patch introduces a counter of VCPUs that have
LVT0 set to NMI mode. Only if the counter > 0, we push the PIT ticks via
all LAPIC LVT0 lines to enable NMI watchdog support.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Acked-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/i8254.c | 11 ++++++-----
arch/x86/kvm/lapic.c | 23 ++++++++++++++++++++---
3 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 59c3ae1..09e6c56 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -361,6 +361,7 @@ struct kvm_arch{
struct kvm_ioapic *vioapic;
struct kvm_pit *vpit;
struct hlist_head irq_ack_notifier_list;
+ int vapics_in_nmi_mode;

int round_robin_prev_vcpu;
unsigned int tss_addr;
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index b6fcf5a..e665d1c 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -620,11 +620,12 @@ static void __inject_pit_timer_intr(struct kvm *kvm)
* LVT0 to NMI delivery. Other PIC interrupts are just sent to
* VCPU0, and only if its LVT0 is in EXTINT mode.
*/
- for (i = 0; i < KVM_MAX_VCPUS; ++i) {
- vcpu = kvm->vcpus[i];
- if (vcpu)
- kvm_apic_nmi_wd_deliver(vcpu);
- }
+ if (kvm->arch.vapics_in_nmi_mode > 0)
+ for (i = 0; i < KVM_MAX_VCPUS; ++i) {
+ vcpu = kvm->vcpus[i];
+ if (vcpu)
+ kvm_apic_nmi_wd_deliver(vcpu);
+ }
}

void kvm_inject_pit_timer_irqs(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 0b0d413..afac68c 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -130,6 +130,11 @@ static inline int apic_lvtt_period(struct kvm_lapic *apic)
return apic_get_reg(apic, APIC_LVTT) & APIC_LVT_TIMER_PERIODIC;
}

+static inline int apic_lvt_nmi_mode(u32 lvt_val)
+{
+ return (lvt_val & (APIC_MODE_MASK | APIC_LVT_MASKED)) == APIC_DM_NMI;
+}
+
static unsigned int apic_lvt_mask[APIC_LVT_NUM] = {
LVT_MASK | APIC_LVT_TIMER_PERIODIC, /* LVTT */
LVT_MASK | APIC_MODE_MASK, /* LVTTHMR */
@@ -672,6 +677,20 @@ static void start_apic_timer(struct kvm_lapic *apic)
apic->timer.period)));
}

+static void apic_manage_nmi_watchdog(struct kvm_lapic *apic, u32 lvt0_val)
+{
+ int nmi_wd_enabled = apic_lvt_nmi_mode(apic_get_reg(apic, APIC_LVT0));
+
+ if (apic_lvt_nmi_mode(lvt0_val)) {
+ if (!nmi_wd_enabled) {
+ apic_debug("Receive NMI setting on APIC_LVT0 "
+ "for cpu %d\n", apic->vcpu->vcpu_id);
+ apic->vcpu->kvm->arch.vapics_in_nmi_mode++;
+ }
+ } else if (nmi_wd_enabled)
+ apic->vcpu->kvm->arch.vapics_in_nmi_mode--;
+}
+
static void apic_mmio_write(struct kvm_io_device *this,
gpa_t address, int len, const void *data)
{
@@ -753,9 +772,7 @@ static void apic_mmio_write(struct kvm_io_device *this,
break;

case APIC_LVT0:
- if (val == APIC_DM_NMI)
- apic_debug("Receive NMI setting on APIC_LVT0 "
- "for cpu %d\n", apic->vcpu->vcpu_id);
+ apic_manage_nmi_watchdog(apic, val);
case APIC_LVTT:
case APIC_LVTTHMR:
case APIC_LVTPC:
--
1.6.0.3