[PATCH v4 3/4] KVM: x86: Add lowest-priority support for vt-d posted-interrupts

From: Feng Wu
Date: Mon Jan 25 2016 - 04:13:05 EST


Use vector-hashing to deliver lowest-priority interrupts for
VT-d posted-interrupts. This patch extends kvm_intr_is_single_vcpu()
to support lowest-priority handling.

Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
v4:
- Recover the function name to 'kvm_intr_is_single_vcpu'
- Stylistic changes

v3:
- Remove unnecessary check in fast irq delivery patch
- print a error message only once for each guest when we find hardware
disabled LAPIC during interrupt injection.

arch/x86/kvm/lapic.c | 56 +++++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 49 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 1a4ca1d..1520d1a 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -798,6 +798,20 @@ out:
return ret;
}

+/*
+ * This routine tries to handler interrupts in posted mode, here is how
+ * it deals with different cases:
+ * - For single-destination interrupts, handle it in posted mode
+ * - Else if vector hashing is enabled and it is a lowest-priority
+ * interrupt, handle it in posted mode and use the following mechanism
+ * to find the destinaiton vCPU.
+ * 1. For lowest-priority interrupts, store all the possible
+ * destination vCPUs in an array.
+ * 2. Use "guest vector % max number of destination vCPUs" to find
+ * the right destination vCPU in the array for the lowest-priority
+ * interrupt.
+ * - Otherwise, use remapped mode to inject the interrupt.
+ */
bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq,
struct kvm_vcpu **dest_vcpu)
{
@@ -839,16 +853,44 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq,
if (cid >= ARRAY_SIZE(map->logical_map))
goto out;

- for_each_set_bit(i, &bitmap, 16) {
- dst = map->logical_map[cid][i];
- if (++r == 2)
+ if (kvm_vector_hashing_enabled() &&
+ kvm_lowest_prio_delivery(irq)) {
+ int idx;
+ unsigned int dest_vcpus;
+
+ dest_vcpus = hweight16(bitmap);
+ if (dest_vcpus == 0)
goto out;
- }

- if (dst && kvm_apic_present(dst->vcpu))
+ idx = kvm_vector_to_index(irq->vector, dest_vcpus,
+ &bitmap, 16);
+
+ /*
+ * We may find a hardware disabled LAPIC here, if that
+ * is the case, print out a error message once for each
+ * guest and return
+ */
+ dst = map->logical_map[cid][idx];
+ if (!dst && !kvm->arch.disabled_lapic_found) {
+ kvm->arch.disabled_lapic_found = true;
+ printk(KERN_INFO
+ "Disabled LAPIC found during irq injection\n");
+ goto out;
+ }
+
*dest_vcpu = dst->vcpu;
- else
- goto out;
+ } else {
+ for_each_set_bit(i, &bitmap, 16) {
+ dst = map->logical_map[cid][i];
+ if (++r == 2)
+ goto out;
+ }
+
+ if (dst && kvm_apic_present(dst->vcpu))
+ *dest_vcpu = dst->vcpu;
+ else
+ goto out;
+ }
}

ret = true;
--
2.1.0