Re: [Qemu-devel] [RFC v3 05/15] hw/arm/virt: handle max_vm_phys_shift conflicts on migration

[David Hildenbrand <david@redhat.com>]

On 03.07.2018 09:19, Eric Auger wrote:
> When migrating a VM, we must make sure the destination host
> supports as many IPA bits as the source. Otherwise the migration
> must fail.
> 
> We add a VMState infrastructure to machvirt. On pre_save(),
> the current source max_vm_phys_shift is saved.
> 
> On destination, we cannot use this information when creating the
> VM. The VM is created using the max value reported by the
> destination host - or the kvm_type inherited value -. However on
> post_load() we can check that this value is compatible with the
> source saved value.

Just wondering, how exactly is the guest able to detect the 42b (e.g. vs
42b) configuration?

> 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> ---
>  hw/arm/virt.c         | 37 +++++++++++++++++++++++++++++++++++++
>  include/hw/arm/virt.h |  2 ++
>  2 files changed, 39 insertions(+)
> 
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 04a32de..5a4d0bf 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -1316,6 +1316,40 @@ static uint64_t virt_cpu_mp_affinity(VirtMachineState *vms, int idx)
>      return arm_cpu_mp_affinity(idx, clustersz);
>  }
>  
> +static int virt_post_load(void *opaque, int version_id)
> +{
> +    VirtMachineState *vms = (VirtMachineState *)opaque;
> +
> +    if (vms->max_vm_phys_shift < vms->source_max_vm_phys_shift) {
> +        error_report("This host kernel only supports %d IPA bits whereas "
> +                     "the guest requires %d GPA bits", vms->max_vm_phys_shift,
> +                     vms->source_max_vm_phys_shift);
> +        return -1;
> +    }
> +    return 0;
> +}
> +
> +static int virt_pre_save(void *opaque)
> +{
> +    VirtMachineState *vms = (VirtMachineState *)opaque;
> +
> +    vms->source_max_vm_phys_shift = vms->max_vm_phys_shift;
> +    return 0;
> +}
> +
> +static const VMStateDescription vmstate_virt = {
> +    .name = "virt",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .post_load = virt_post_load,
> +    .pre_save = virt_pre_save,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_INT32(source_max_vm_phys_shift, VirtMachineState),
> +        VMSTATE_END_OF_LIST()
> +    },
> +};
> +
> +
>  static void machvirt_init(MachineState *machine)
>  {
>      VirtMachineState *vms = VIRT_MACHINE(machine);
> @@ -1537,6 +1571,7 @@ static void machvirt_init(MachineState *machine)
>  
>      vms->machine_done.notify = virt_machine_done;
>      qemu_add_machine_init_done_notifier(&vms->machine_done);
> +    vmstate_register(NULL, 0, &vmstate_virt, vms);
>  }
>  
>  static bool virt_get_secure(Object *obj, Error **errp)
> @@ -1727,6 +1762,7 @@ static HotplugHandler *virt_machine_get_hotplug_handler(MachineState *machine,
>  
>  static int virt_kvm_type(MachineState *ms, const char *type_str)
>  {
> +    VirtMachineState *vms = VIRT_MACHINE(ms);
>      int max_vm_phys_shift, ret = 0;
>      uint64_t type;
>  
> @@ -1747,6 +1783,7 @@ static int virt_kvm_type(MachineState *ms, const char *type_str)
>      }
>      ret = max_vm_phys_shift;
>  out:
> +    vms->max_vm_phys_shift = (max_vm_phys_shift > 0) ? ret : 40;
>      return ret;
>  }
>  
> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> index 1a90ffc..91f6de2 100644
> --- a/include/hw/arm/virt.h
> +++ b/include/hw/arm/virt.h
> @@ -125,6 +125,8 @@ typedef struct {
>      uint32_t iommu_phandle;
>      int psci_conduit;
>      char *kvm_type;
> +    int32_t max_vm_phys_shift;
> +    int32_t source_max_vm_phys_shift;
>  } VirtMachineState;
>  
>  #define VIRT_ECAM_ID(high) (high ? VIRT_PCIE_ECAM_HIGH : VIRT_PCIE_ECAM)
> 


-- 

Thanks,

David / dhildenb