[PATCH RFC 11/13] iommu/vt-d: Add an irq_chip for posted MSIs

[Jacob Pan]

With posted MSIs, end of interrupt is handled by the notification
handler. Each MSI handler does not go through local APIC IRR, ISR
processing. There's no need to do apic_eoi() in those handlers.

Add a new acpi_ack_irq_no_eoi() for the posted MSI IR chip. At runtime
the call trace looks like:

__sysvec_posted_msi_notification() {
  irq_chip_ack_parent() {
    apic_ack_irq_no_eoi();
  }
  handle_irq_event() {
    handle_irq_event_percpu() {
       driver_handler()
    }
  }

IO-APIC IR is excluded the from posted MSI, we need to make sure it
still performs EOI.

Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/apic.h         |  1 +
 arch/x86/kernel/apic/io_apic.c      |  2 +-
 arch/x86/kernel/apic/vector.c       |  5 ++++
 drivers/iommu/intel/irq_remapping.c | 38 ++++++++++++++++++++++++++++-
 4 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 5af4ec1a0f71..a88015d5638b 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -485,6 +485,7 @@ static inline void apic_setup_apic_calls(void) { }
 #endif /* CONFIG_X86_LOCAL_APIC */
 
 extern void apic_ack_irq(struct irq_data *data);
+extern void apic_ack_irq_no_eoi(struct irq_data *data);
 
 static inline bool lapic_vector_set_in_irr(unsigned int vector)
 {
diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 00da6cf6b07d..ca398ee9075b 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -1993,7 +1993,7 @@ static struct irq_chip ioapic_ir_chip __read_mostly = {
 	.irq_startup		= startup_ioapic_irq,
 	.irq_mask		= mask_ioapic_irq,
 	.irq_unmask		= unmask_ioapic_irq,
-	.irq_ack		= irq_chip_ack_parent,
+	.irq_ack		= apic_ack_irq,
 	.irq_eoi		= ioapic_ir_ack_level,
 	.irq_set_affinity	= ioapic_set_affinity,
 	.irq_retrigger		= irq_chip_retrigger_hierarchy,
diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
index 14fc33cfdb37..01223ac4f57a 100644
--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -911,6 +911,11 @@ void apic_ack_irq(struct irq_data *irqd)
 	apic_eoi();
 }
 
+void apic_ack_irq_no_eoi(struct irq_data *irqd)
+{
+	irq_move_irq(irqd);
+}
+
 void apic_ack_edge(struct irq_data *irqd)
 {
 	irq_complete_move(irqd_cfg(irqd));
diff --git a/drivers/iommu/intel/irq_remapping.c b/drivers/iommu/intel/irq_remapping.c
index 29b9e55dcf26..f2870d3c8313 100644
--- a/drivers/iommu/intel/irq_remapping.c
+++ b/drivers/iommu/intel/irq_remapping.c
@@ -1233,6 +1233,42 @@ static struct irq_chip intel_ir_chip = {
 	.irq_set_vcpu_affinity	= intel_ir_set_vcpu_affinity,
 };
 
+/*
+ * With posted MSIs, all vectors are multiplexed into a single notification
+ * vector. Devices MSIs are then dispatched in a demux loop where
+ * EOIs can be coalesced as well.
+ *
+ * IR chip "INTEL-IR-POST" does not do EOI on ACK instead letting posted
+ * interrupt notification handler to perform EOI.
+ *
+ * For the example below, 3 MSIs are coalesced in one CPU notification. Only
+ * one apic_eoi() is needed.
+ *
+ * __sysvec_posted_msi_notification() {
+ * irq_enter()
+ *	handle_edge_irq()
+ *		irq_chip_ack_parent()
+ *			apic_ack_irq_no_eoi()
+ *		handle_irq()
+ *	handle_edge_irq()
+ *		irq_chip_ack_parent()
+ *			apic_ack_irq_no_eoi()
+ *		handle_irq()
+ *	handle_edge_irq()
+ *		irq_chip_ack_parent()
+ *			apic_ack_irq_no_eoi()
+ *		handle_irq()
+ *	apic_eoi()
+ * irq_exit()
+ */
+static struct irq_chip intel_ir_chip_post_msi = {
+	.name			= "INTEL-IR-POST",
+	.irq_ack		= apic_ack_irq_no_eoi,
+	.irq_set_affinity	= intel_ir_set_affinity,
+	.irq_compose_msi_msg	= intel_ir_compose_msi_msg,
+	.irq_set_vcpu_affinity	= intel_ir_set_vcpu_affinity,
+};
+
 static void fill_msi_msg(struct msi_msg *msg, u32 index, u32 subhandle)
 {
 	memset(msg, 0, sizeof(*msg));
@@ -1361,7 +1397,7 @@ static int intel_irq_remapping_alloc(struct irq_domain *domain,
 
 		irq_data->hwirq = (index << 16) + i;
 		irq_data->chip_data = ird;
-		irq_data->chip = &intel_ir_chip;
+		irq_data->chip = posted_msi_supported() ? &intel_ir_chip_post_msi : &intel_ir_chip;
 		intel_irq_remapping_prepare_irte(ird, irq_cfg, info, index, i);
 		irq_set_status_flags(virq + i, IRQ_MOVE_PCNTXT);
 	}
-- 
2.25.1