[RFC Patch V1] genirq: Introduce irq_set_vcpu_affinity() to target an interrupt to a VCPU

From: Jiang Liu
Date: Thu Nov 20 2014 - 02:06:58 EST

With Posted-Interrupts support in Intel CPU and IOMMU, an external
interrupt from assigned-devices could be directly delivered to a
virtual CPU in a virtual machine. Instead of hacking KVM and Intel
IOMMU drivers, we propose a platform independent interface to target
an interrupt to a specific virtual CPU in a virtual machine, or set
virtual CPU affinity for an interrupt.

By adopting this new interface and the hierarchy irqdomain, we could
easily support posted-interrupts on Intel platforms, and also provide
flexible enough interfaces for other platforms to support similar

We may also cooperate between set_affinity() and set_vcpu_affinity()
in IRQ core or irq chip drivers.

Here is the usage scenario for this interface:
Guest update MSI/MSI-X interrupt configuratoin
-->QEMU and KVM handle this
-->KVM call this interface (passing posted interrupts descriptor
and guest vector)
-->irq core will transfer the control to IOMMU
-->IOMMU will do the real work of updating IRTE (IRTE has new
format for VT-d Posted-Interrupts)

You can find the VT-d Posted-Interrtups Spec. in the following URL:

Signed-off-by: Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx>
Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
include/linux/irq.h | 6 ++++++
kernel/irq/manage.c | 19 +++++++++++++++++++
2 files changed, 25 insertions(+)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index 8badf34baf0f..0a3c8ac38ffb 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -29,6 +29,7 @@
struct seq_file;
struct module;
struct msi_msg;
+struct irq_vcpu_id;

* IRQ line status.
@@ -323,6 +324,8 @@ static inline irq_hw_number_t irqd_to_hwirq(struct irq_data *d)
* irq_request_resources
* @irq_compose_msi_msg: optional to compose message content for MSI
* @irq_write_msi_msg: optional to write message content for MSI
+ * @irq_set_vcpu_affinity: optional to target a virtual CPU in a virtual
+ * machine
* @flags: chip specific flags
struct irq_chip {
@@ -362,6 +365,8 @@ struct irq_chip {
void (*irq_compose_msi_msg)(struct irq_data *data, struct msi_msg *msg);
void (*irq_write_msi_msg)(struct irq_data *data, struct msi_msg *msg);

+ int (*irq_set_vcpu_affinity)(struct irq_data *data, struct irq_vcpu_id *vcpu_id);
unsigned long flags;

@@ -415,6 +420,7 @@ extern void irq_cpu_online(void);
extern void irq_cpu_offline(void);
extern int irq_set_affinity_locked(struct irq_data *data,
const struct cpumask *cpumask, bool force);
+extern int irq_set_vcpu_affinity(unsigned int irq, struct irq_vcpu_id *vcpu_id);

void irq_move_irq(struct irq_data *data);
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 80692373abd6..4ae8f243293a 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -247,6 +247,25 @@ int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m)

+int irq_set_vcpu_affinity(unsigned int irq, struct irq_vcpu_id *vcpu_id)
+ struct irq_desc *desc = irq_to_desc(irq);
+ struct irq_chip *chip;
+ unsigned long flags;
+ int ret = -ENOSYS;
+ if (!desc)
+ return -EINVAL;
+ raw_spin_lock_irqsave(&desc->lock, flags);
+ chip = desc->irq_data.chip;
+ if (chip && chip->irq_set_vcpu_affinity)
+ ret = chip->irq_set_vcpu_affinity(&desc->irq_data, vcpu_id);
+ raw_spin_unlock_irqrestore(&desc->lock, flags);
+ return ret;
static void irq_affinity_notify(struct work_struct *work)
struct irq_affinity_notify *notify =

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