On Mon, Aug 18, 2025 at 09:11:27PM +0800, Yanfei Xu wrote:
> 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.1...@bytedance.com>
> Signed-off-by: Yanfei Xu <yanfei...@bytedance.com>
> ---
> hw/intc/apic_common.c | 1 +
> include/migration/vmstate.h | 1 +
> 2 files changed, 2 insertions(+)
>
> diff --git a/hw/intc/apic_common.c b/hw/intc/apic_common.c
> index 37a7a7019d..394fe02013 100644
> --- 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 1ff7bd9ac4..22e988c5db 100644
> --- 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 */
As the list grows, maybe it's a good idea we start to document exactly the
reasons inline into the enum. Can sure be done on top. This patch alone
looks like stable material..
Reviewed-by: Peter Xu <pet...@redhat.com>
> MIG_PRI_GICV3_ITS, /* Must happen before PCI devices */
> MIG_PRI_GICV3, /* Must happen before the ITS */
> MIG_PRI_MAX,
> --
> 2.20.1
>
--
Peter Xu
