Re: [Qemu-devel] [RFC PATCH 1/2] target-ppc: migrate interrupt vectors address for spapr VM

["Cédric Le Goater" <clg@fr.ibm.com>]

On 03/22/2016 01:15 AM, David Gibson wrote:
> On Mon, Mar 21, 2016 at 05:51:22PM +0100, Cédric Le Goater wrote:
>> On 03/21/2016 05:18 PM, Thomas Huth wrote:
>>> On 21.03.2016 15:02, Cédric Le Goater wrote:
>>>> This address is changed by the linux kernel using the H_SET_MODE hcall
>>>> and needs to be migrated in order to restart a spapr VM running in
>>>> TCG. Other platforms should not be affected.
>>>>
>>>> Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
>>>> ---
>>>>  target-ppc/machine.c | 3 +++
>>>>  1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/target-ppc/machine.c b/target-ppc/machine.c
>>>> index 692121e98319..a418d463db83 100644
>>>> --- a/target-ppc/machine.c
>>>> +++ b/target-ppc/machine.c
>>>> @@ -553,6 +553,9 @@ const VMStateDescription vmstate_ppc_cpu = {
>>>>          VMSTATE_UINTTL(env.hflags_nmsr, PowerPCCPU),
>>>>          /* FIXME: access_type? */
>>>>  
>>>> +        /* Effective Address of interrupt vectors */
>>>> +        VMSTATE_UINTTL(env.excp_prefix, PowerPCCPU),
>>>> +
>>>>          /* Sanity checking */
>>>>          VMSTATE_UINTTL_EQUAL(env.msr_mask, PowerPCCPU),
>>>>          VMSTATE_UINT64_EQUAL(env.insns_flags, PowerPCCPU),
>>>
>>> I'm really no expert with all this migration stuff, but don't you have
>>> to bump the version_id when you add new fields to the vmstate?
>>> ... and/or use VMSTATE_UINTTL_V() so that migration from older versions
>>> of QEMU to the current one also still works with KVM? For example, is it
>>> still possible to migrate from QEMU 2.5 to QEMU 2.6 in KVM if you only
>>> use VMSTATE_UINTTL without the _V suffix?
>>
>> Yes. You are right. I think we need something like below.
>>
>> Thanks,
>>
>> C.
>>
>>
>> target-ppc: migrate interrupt vectors address for spapr VM
>>
>> This address is changed by the linux kernel using the H_SET_MODE hcall
>> and needs to be migrated in order to restart a spapr VM running in
>> TCG. Other platforms should not be affected.
>>
>> Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
>> ---
>>  target-ppc/machine.c |    5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> Index: qemu-dgibson-for-2.6.git/target-ppc/machine.c
>> ===================================================================
>> --- qemu-dgibson-for-2.6.git.orig/target-ppc/machine.c
>> +++ qemu-dgibson-for-2.6.git/target-ppc/machine.c
>> @@ -522,7 +522,7 @@ static const VMStateDescription vmstate_
>>  
>>  const VMStateDescription vmstate_ppc_cpu = {
>>      .name = "cpu",
>> -    .version_id = 5,
>> +    .version_id = 6,
>>      .minimum_version_id = 5,
>>      .minimum_version_id_old = 4,
>>      .load_state_old = cpu_load_old,
>> @@ -553,6 +553,9 @@ const VMStateDescription vmstate_ppc_cpu
>>          VMSTATE_UINTTL(env.hflags_nmsr, PowerPCCPU),
>>          /* FIXME: access_type? */
>>  
>> +        /* Effective Address of interrupt vectors */
>> +        VMSTATE_UINTTL_V(env.excp_prefix, PowerPCCPU, 6),
> 
> 
> So, I dislike putting what's essentially emulator internal state (as
> opposed to architected state) into the migration stream if we can
> possibly avoid it.
> 
> I think recalculating excp_prefix from the MSR on incoming migration
> is the correct approach here - I see that there are bugs with that in
> the other patch, but so far I'm not seeing a reason to migrate
> excp_prefix itself.

OK. It seems quite feasible as we can compute the value from the LPCR_AIL 
bits in SPR_LPCR. I will give it a try.

Thanks,

C.



>>          /* Sanity checking */
>>          VMSTATE_UINTTL_EQUAL(env.msr_mask, PowerPCCPU),
>>          VMSTATE_UINT64_EQUAL(env.insns_flags, PowerPCCPU),
>>
>>
>>  
>>>  Thomas
>>>
>>
>