KVM: dont clear TMR on EOI
Intel spec says that TMR needs to be set/cleared
when IRR is set, but kvm also clears it on EOI.
I did some tests on a real (AMD based) system,
and I see same TMR values both before
and after EOI, so I think it's a minor bug in kvm.
This patch fixes TMR to be set/cleared on IRR set
only as per spec.
And now that we don't clear TMR, we can save
an atomic read of TMR on EOI that's not propagated
to ioapic, by checking whether ioapic needs
a specific vector first and calculating
the mode afterwards.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 8584322..992b4ea 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -92,6 +92,11 @@
return test_and_clear_bit(VEC_POS(vec), (bitmap) + REG_POS(vec));
}
+static inline int apic_test_vector(int vec, void *bitmap)
+{
+ return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec));
+}
+
static inline void apic_set_vector(int vec, void *bitmap)
{
set_bit(VEC_POS(vec), (bitmap) + REG_POS(vec));
@@ -480,7 +485,6 @@
static void apic_set_eoi(struct kvm_lapic *apic)
{
int vector = apic_find_highest_isr(apic);
- int trigger_mode;
/*
* Not every write EOI will has corresponding ISR,
* one example is when Kernel check timer on setup_IO_APIC
@@ -491,12 +495,15 @@
apic_clear_vector(vector, apic->regs + APIC_ISR);
apic_update_ppr(apic);
- if (apic_test_and_clear_vector(vector, apic->regs + APIC_TMR))
- trigger_mode = IOAPIC_LEVEL_TRIG;
- else
- trigger_mode = IOAPIC_EDGE_TRIG;
- if (!(apic_get_reg(apic, APIC_SPIV) & APIC_SPIV_DIRECTED_EOI))
+ if (!(apic_get_reg(apic, APIC_SPIV) & APIC_SPIV_DIRECTED_EOI) &&
+ kvm_ioapic_handles_vector(apic->vcpu->kvm, vector)) {
+ int trigger_mode;
+ if (apic_test_vector(vector, apic->regs + APIC_TMR))
+ trigger_mode = IOAPIC_LEVEL_TRIG;
+ else
+ trigger_mode = IOAPIC_EDGE_TRIG;
kvm_ioapic_update_eoi(apic->vcpu->kvm, vector, trigger_mode);
+ }
kvm_make_request(KVM_REQ_EVENT, apic->vcpu);
}