Re: [PATCH] migration: ensure APIC is loaded prior to VFIO PCI devices

[Peter Xu <peterx@redhat.com>]

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.1023@bytedance.com>
> Signed-off-by: Yanfei Xu <yanfei.xu@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 */
>      MIG_PRI_GICV3_ITS,          /* Must happen before PCI devices */
>      MIG_PRI_GICV3,              /* Must happen before the ITS */
>      MIG_PRI_MAX,
> -- 
> 2.20.1
> 

+Cedric, +Alex

queued.

-- 
Peter Xu