migration: ensure APIC is loaded prior to VFIO PCI devices

The load procedure of VFIO PCI devices involves setting up IRT
for each VFIO PCI devices. This requires determining whether an
interrupt is single-destination interrupt to decide between
Posted Interrupt(PI) or remapping mode for the IRTE. However,
determining this may require accessing the VM's APIC registers.

For example:
ioctl(vbasedev->fd, VFIO_DEVICE_SET_IRQS, irqs)
  ...
    kvm_arch_irq_bypass_add_producer
      kvm_x86_call(pi_update_irte)
        vmx_pi_update_irte
          kvm_intr_is_single_vcpu

If the LAPIC has not been loaded yet, interrupts will use remapping
mode. To prevent the fallback of interrupt mode, keep APIC is always
loaded prior to VFIO PCI devices.

Signed-off-by: Yicong Shen <shenyicong.1023@bytedance.com>
Signed-off-by: Yanfei Xu <yanfei.xu@bytedance.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/20250818131127.1021648-1-yanfei.xu@bytedance.com
Signed-off-by: Peter Xu <peterx@redhat.com>

diff --git a/hw/intc/apic_common.c b/hw/intc/apic_common.c
index 37a7a7019d33ccc6a7a45f78affcfc23dc649d77..394fe020134f4ebdb868fd8b19a3876e6bfe6937 100644 (file)
--- a/hw/intc/apic_common.c
+++ b/hw/intc/apic_common.c
@@ -379,6 +379,7 @@ static const VMStateDescription vmstate_apic_common = {
     .pre_load = apic_pre_load,
     .pre_save = apic_dispatch_pre_save,
     .post_load = apic_dispatch_post_load,
+    .priority = MIG_PRI_APIC,
     .fields = (const VMStateField[]) {
         VMSTATE_UINT32(apicbase, APICCommonState),
         VMSTATE_UINT8(id, APICCommonState),

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 5567fd78d0404f5fa8bfc1c9887d63de0cf3b22c..6f5a9fed68bde3559380060ffd4abd724f508b82 100644 (file)
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -163,6 +163,7 @@ typedef enum {
     MIG_PRI_IOMMU,              /* Must happen before PCI devices */
     MIG_PRI_PCI_BUS,            /* Must happen before IOMMU */
     MIG_PRI_VIRTIO_MEM,         /* Must happen before IOMMU */
+    MIG_PRI_APIC,               /* Must happen before PCI devices */
     MIG_PRI_GICV3_ITS,          /* Must happen before PCI devices */
     MIG_PRI_GICV3,              /* Must happen before the ITS */
     MIG_PRI_MAX,