Re: [RESEND PATCH 1/7] target/arm/machine: Improve traces on register mismatch during migration

[Eric Auger <eric.auger@redhat.com>]

On 10/17/25 4:59 PM, Cornelia Huck wrote:
> On Thu, Oct 16 2025, Eric Auger <eric.auger@redhat.com> wrote:
>
> More information is really valuable here. I have some nits :)
>
>> Currently whenthe number of KVM registers exposed by the source is
> s/whenthe/when the/
>
>> larger than the one exposed on the destination, the migration fails
>> with: "failed to load cpu:cpreg_vmstate_array_len"
>>
>> This gives no information about which registers are causing the trouble.
>>
>> This patches rework the target/arm/machine code so that it becomes
> s/patches rework/patch reworks/
>
>> able to handle an input stream with a larger set of registers than
>> the destination and print useful information about which registers
>> are causing the trouble. The migration outcome is unchanged:
>> - unexpected registers still will fail the migration
>> - missing ones are print but will not fail the migration, as done today.
> s/print/printed/
>
>> The input stream can contain MAX_CPREG_VMSTATE_ANOMALIES(10) extra
>> registers compared to what exists on the target.
>>
>> If there are more registers we will still hit the previous
>> "load cpu:cpreg_vmstate_array_len" error.
>>
>> At most, MAX_CPREG_VMSTATE_ANOMALIES missing registers
>> and MAX_CPREG_VMSTATE_ANOMALIES unexpected registers are print.
> s/print/printed/
>
> If we really get tons of register discrepancies, I'd expect the reason for
> that to be something more obvious, so limiting should be fine.
>
>> Example:
>>
>> qemu-system-aarch64: kvm_arm_cpu_post_load Missing register in input stream: 0 0x6030000000160003 fw feat reg 3
>> qemu-system-aarch64: kvm_arm_cpu_post_load Unexpected register in input stream: 0 0x603000000013c103 op0:3 op1:0 crn:2 crm:0 op2:3
>> qemu-system-aarch64: kvm_arm_cpu_post_load Unexpected register in input stream: 1 0x603000000013c512 op0:3 op1:0 crn:10 crm:2 op2:2
>> qemu-system-aarch64: kvm_arm_cpu_post_load Unexpected register in input stream: 2 0x603000000013c513 op0:3 op1:0 crn:10 crm:2 op2:3
>> qemu-system-aarch64: error while loading state for instance 0x0 of device 'cpu'
>> qemu-system-aarch64: load of migration failed: Operation not permitted
>>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>> ---
>>  target/arm/cpu.h        |  6 +++++
>>  target/arm/kvm.c        | 23 ++++++++++++++++
>>  target/arm/machine.c    | 58 ++++++++++++++++++++++++++++++++++++-----
>>  target/arm/trace-events |  7 +++++
>>  4 files changed, 88 insertions(+), 6 deletions(-)
>>
>> diff --git a/target/arm/cpu.h b/target/arm/cpu.h
>> index bf221e6f97..a7ed3f34f8 100644
>> --- a/target/arm/cpu.h
>> +++ b/target/arm/cpu.h
>> @@ -936,6 +936,12 @@ struct ArchCPU {
>>      uint64_t *cpreg_vmstate_values;
>>      int32_t cpreg_vmstate_array_len;
>>  
>> +    #define MAX_CPREG_VMSTATE_ANOMALIES 10
>> +    uint64_t cpreg_vmstate_missing_indexes[MAX_CPREG_VMSTATE_ANOMALIES];
>> +    int32_t cpreg_vmstate_missing_indexes_array_len;
>> +    uint64_t cpreg_vmstate_unexpected_indexes[MAX_CPREG_VMSTATE_ANOMALIES];
>> +    int32_t cpreg_vmstate_unexpected_indexes_array_len;
> "indices"?

Originally we had
   uint64_t *cpreg_vmstate_indexes;
so I reused the same terminology

As a non native english speaker I don't know if the usage is wrong. I
thought some references on the net though

Eric
>
>> +
>>      DynamicGDBFeatureInfo dyn_sysreg_feature;
>>      DynamicGDBFeatureInfo dyn_svereg_feature;
>>      DynamicGDBFeatureInfo dyn_smereg_feature;
> (...)
>