[v4] Mitigation of "failed to load cpu:cpreg_vmstate_array_len" migration failures

[PATCH v4 08/10] hw/arm/virt: Declare AArch32 DBGDTRTX as safe to ignore in incoming stream

Posted by Eric Auger 1 month, 2 weeks ago

With the new infrastructure in place it is now feasible to teach
qemu that it is safe to ignore a sysreg in the incoming migration
stream. So with the plan to revert commit 4f2b82f60431 ("target/arm:
Reinstate bogus AArch32 DBGDTRTX register for migration compat) from
qemu 11 onwards, let's add a compat in 10.2 machine options stating
that this reg is safe to ignore. from 11.0 onwards we will not need
that register anymore.

Signed-off-by: Eric Auger <eric.auger@redhat.com>

---

v3 -> v4:
- add a comment related to DBGDTRTX (Connie)
---
 hw/arm/virt.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index ec0af8e6e7..00948887a2 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -100,6 +100,15 @@ static GlobalProperty arm_virt_compat_defaults[] = {
 static const size_t arm_virt_compat_defaults_len =
     G_N_ELEMENTS(arm_virt_compat_defaults);
 
+/* Register erronously exposed on 10.2 and earlier */
+#define DBGDTRTX 0x40200000200e0298
+
+static GlobalProperty arm_virt_compat_10_2[] = {
+    { TYPE_ARM_CPU, "x-mig-safe-missing-regs", stringify(DBGDTRTX)},
+};
+static const size_t arm_virt_compat_10_2_len =
+    G_N_ELEMENTS(arm_virt_compat_10_2);
+
 /*
  * This cannot be called from the virt_machine_class_init() because
  * TYPE_VIRT_MACHINE is abstract and mc->compat_props g_ptr_array_new()
@@ -3536,6 +3545,7 @@ type_init(machvirt_machine_init);
 
 static void virt_machine_10_2_options(MachineClass *mc)
 {
+    compat_props_add(mc->compat_props, arm_virt_compat_10_2, arm_virt_compat_10_2_len);
 }
 DEFINE_VIRT_MACHINE_AS_LATEST(10, 2)
 
-- 
2.52.0

Re: [PATCH v4 08/10] hw/arm/virt: Declare AArch32 DBGDTRTX as safe to ignore in incoming stream

Posted by Cornelia Huck 1 month, 2 weeks ago

On Mon, Dec 22 2025, Eric Auger <eric.auger@redhat.com> wrote:

> With the new infrastructure in place it is now feasible to teach
> qemu that it is safe to ignore a sysreg in the incoming migration
> stream. So with the plan to revert commit 4f2b82f60431 ("target/arm:
> Reinstate bogus AArch32 DBGDTRTX register for migration compat) from

<pedantic> Missing closing '"' </pedantic>

> qemu 11 onwards, let's add a compat in 10.2 machine options stating

QEMU 11.0?

> that this reg is safe to ignore. from 11.0 onwards we will not need
> that register anymore.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
>
> v3 -> v4:
> - add a comment related to DBGDTRTX (Connie)
> ---
>  hw/arm/virt.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index ec0af8e6e7..00948887a2 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -100,6 +100,15 @@ static GlobalProperty arm_virt_compat_defaults[] = {
>  static const size_t arm_virt_compat_defaults_len =
>      G_N_ELEMENTS(arm_virt_compat_defaults);
>  
> +/* Register erronously exposed on 10.2 and earlier */
> +#define DBGDTRTX 0x40200000200e0298
> +
> +static GlobalProperty arm_virt_compat_10_2[] = {
> +    { TYPE_ARM_CPU, "x-mig-safe-missing-regs", stringify(DBGDTRTX)},
> +};
> +static const size_t arm_virt_compat_10_2_len =
> +    G_N_ELEMENTS(arm_virt_compat_10_2);
> +
>  /*
>   * This cannot be called from the virt_machine_class_init() because
>   * TYPE_VIRT_MACHINE is abstract and mc->compat_props g_ptr_array_new()
> @@ -3536,6 +3545,7 @@ type_init(machvirt_machine_init);
>  
>  static void virt_machine_10_2_options(MachineClass *mc)
>  {
> +    compat_props_add(mc->compat_props, arm_virt_compat_10_2, arm_virt_compat_10_2_len);
>  }
>  DEFINE_VIRT_MACHINE_AS_LATEST(10, 2)
>  

Hm, maybe rebase this on top of the new machine types?

Re: [PATCH v4 08/10] hw/arm/virt: Declare AArch32 DBGDTRTX as safe to ignore in incoming stream

Posted by Eric Auger 1 month ago


On 12/23/25 3:30 PM, Cornelia Huck wrote:
> On Mon, Dec 22 2025, Eric Auger <eric.auger@redhat.com> wrote:
>
>> With the new infrastructure in place it is now feasible to teach
>> qemu that it is safe to ignore a sysreg in the incoming migration
>> stream. So with the plan to revert commit 4f2b82f60431 ("target/arm:
>> Reinstate bogus AArch32 DBGDTRTX register for migration compat) from
> <pedantic> Missing closing '"' </pedantic>
>
>> qemu 11 onwards, let's add a compat in 10.2 machine options stating
> QEMU 11.0?
>
>> that this reg is safe to ignore. from 11.0 onwards we will not need
>> that register anymore.
>>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>
>> ---
>>
>> v3 -> v4:
>> - add a comment related to DBGDTRTX (Connie)
>> ---
>>  hw/arm/virt.c | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>> index ec0af8e6e7..00948887a2 100644
>> --- a/hw/arm/virt.c
>> +++ b/hw/arm/virt.c
>> @@ -100,6 +100,15 @@ static GlobalProperty arm_virt_compat_defaults[] = {
>>  static const size_t arm_virt_compat_defaults_len =
>>      G_N_ELEMENTS(arm_virt_compat_defaults);
>>  
>> +/* Register erronously exposed on 10.2 and earlier */
>> +#define DBGDTRTX 0x40200000200e0298
>> +
>> +static GlobalProperty arm_virt_compat_10_2[] = {
>> +    { TYPE_ARM_CPU, "x-mig-safe-missing-regs", stringify(DBGDTRTX)},
>> +};
>> +static const size_t arm_virt_compat_10_2_len =
>> +    G_N_ELEMENTS(arm_virt_compat_10_2);
>> +
>>  /*
>>   * This cannot be called from the virt_machine_class_init() because
>>   * TYPE_VIRT_MACHINE is abstract and mc->compat_props g_ptr_array_new()
>> @@ -3536,6 +3545,7 @@ type_init(machvirt_machine_init);
>>  
>>  static void virt_machine_10_2_options(MachineClass *mc)
>>  {
>> +    compat_props_add(mc->compat_props, arm_virt_compat_10_2, arm_virt_compat_10_2_len);
>>  }
>>  DEFINE_VIRT_MACHINE_AS_LATEST(10, 2)
>>  
> Hm, maybe rebase this on top of the new machine types?

definitively

Thanks

Eric
>