[PATCH v9 16/18] KVM: Update Posted-Interrupts Descriptor when vCPU is preempted

[Feng Wu]

This patch updates the Posted-Interrupts Descriptor when vCPU
is preempted.

sched out:
- Set 'SN' to suppress furture non-urgent interrupts posted for
the vCPU.

sched in:
- Clear 'SN'
- Change NDST if vCPU is scheduled to a different CPU
- Set 'NV' to POSTED_INTR_VECTOR

Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
v9:
- Check !kvm_arch_has_assigned_device(vcpu->kvm) first, then
  !irq_remapping_cap(IRQ_POSTING_CAP)

v8:
- Add two wrapper fucntion vmx_vcpu_pi_load() and vmx_vcpu_pi_put().
- Only handle VT-d PI related logic when the VM has assigned devices.

 arch/x86/kvm/vmx.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 11bda72..902a67d 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1943,6 +1943,52 @@ static void vmx_load_host_state(struct vcpu_vmx *vmx)
 	preempt_enable();
 }
 
+static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
+{
+	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
+	struct pi_desc old, new;
+	unsigned int dest;
+
+	if (!kvm_arch_has_assigned_device(vcpu->kvm) ||
+		!irq_remapping_cap(IRQ_POSTING_CAP))
+		return;
+
+	do {
+		old.control = new.control = pi_desc->control;
+
+		/*
+		 * If 'nv' field is POSTED_INTR_WAKEUP_VECTOR, there
+		 * are two possible cases:
+		 * 1. After running 'pre_block', context switch
+		 *    happened. For this case, 'sn' was set in
+		 *    vmx_vcpu_put(), so we need to clear it here.
+		 * 2. After running 'pre_block', we were blocked,
+		 *    and woken up by some other guy. For this case,
+		 *    we don't need to do anything, 'pi_post_block'
+		 *    will do everything for us. However, we cannot
+		 *    check whether it is case #1 or case #2 here
+		 *    (maybe, not needed), so we also clear sn here,
+		 *    I think it is not a big deal.
+		 */
+		if (pi_desc->nv != POSTED_INTR_WAKEUP_VECTOR) {
+			if (vcpu->cpu != cpu) {
+				dest = cpu_physical_id(cpu);
+
+				if (x2apic_enabled())
+					new.ndst = dest;
+				else
+					new.ndst = (dest << 8) & 0xFF00;
+			}
+
+			/* set 'NV' to 'notification vector' */
+			new.nv = POSTED_INTR_VECTOR;
+		}
+
+		/* Allow posting non-urgent interrupts */
+		new.sn = 0;
+	} while (cmpxchg(&pi_desc->control, old.control,
+			new.control) != old.control);
+}
 /*
  * Switches to specified vcpu, until a matching vcpu_put(), but assumes
  * vcpu mutex is already taken.
@@ -1993,10 +2039,27 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 		vmcs_writel(HOST_IA32_SYSENTER_ESP, sysenter_esp); /* 22.2.3 */
 		vmx->loaded_vmcs->cpu = cpu;
 	}
+
+	vmx_vcpu_pi_load(vcpu, cpu);
+}
+
+static void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
+{
+	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
+
+	if (!kvm_arch_has_assigned_device(vcpu->kvm) ||
+		!irq_remapping_cap(IRQ_POSTING_CAP))
+		return;
+
+	/* Set SN when the vCPU is preempted */
+	if (vcpu->preempted)
+		pi_set_sn(pi_desc);
 }
 
 static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
 {
+	vmx_vcpu_pi_put(vcpu);
+
 	__vmx_load_host_state(to_vmx(vcpu));
 	if (!vmm_exclusive) {
 		__loaded_vmcs_clear(to_vmx(vcpu)->loaded_vmcs);
@@ -4426,6 +4489,22 @@ static inline bool kvm_vcpu_trigger_posted_interrupt(struct kvm_vcpu *vcpu)
 {
 #ifdef CONFIG_SMP
 	if (vcpu->mode == IN_GUEST_MODE) {
+		struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+		/*
+		 * Currently, we don't support urgent interrupt,
+		 * all interrupts are recognized as non-urgent
+		 * interrupt, so we cannot post interrupts when
+		 * 'SN' is set.
+		 *
+		 * If the vcpu is in guest mode, it means it is
+		 * running instead of being scheduled out and
+		 * waiting in the run queue, and that's the only
+		 * case when 'SN' is set currently, warning if
+		 * 'SN' is set.
+		 */
+		WARN_ON_ONCE(pi_test_sn(&vmx->pi_desc));
+
 		apic->send_IPI_mask(get_cpu_mask(vcpu->cpu),
 				POSTED_INTR_VECTOR);
 		return true;
-- 
2.1.0

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