On 08/11/16 16:29, David Gibson wrote:
> On Fri, Nov 04, 2016 at 06:54:48PM +1100, Alexey Kardashevskiy wrote:
>> On 30/10/16 22:12, David Gibson wrote:
>>> When a vmstate for the ppc cpu was first introduced (a90db15 "target-ppc:
>>> Convert ppc cpu savevm to VMStateDescription"), a VMSTATE_EQUAL was used
>>> to ensure that identical CPU models were used at source and destination
>>> as based on the PVR (Processor Version Register).
>>>
>>> However this was a problem for HV KVM, where due to hardware limitations
>>> we always need to use the real PVR of the host CPU. So, to allow
>>> migration between hosts with "similar enough" CPUs, the PVR check was
>>> removed in 569be9f0 "target-ppc: Remove PVR check from migration". This
>>> left the onus on user / management to only attempt migration between
>>> compatible CPUs.
>>>
>>> Now that we've reworked the handling of compatiblity modes, we have the
>>> information to actually determine if we're making a compatible migration.
>>> So this patch partially restores the PVR check. If the source was running
>>> in a compatibility mode, we just make sure that the destination cpu can
>>> also run in that compatibility mode. However, if the source was running
>>> in "raw" mode, we verify that the destination has the same PVR value.
>>>
>>> Signed-off-by: David Gibson <da...@gibson.dropbear.id.au>
>>> ---
>>> target-ppc/machine.c | 15 +++++++++++----
>>> 1 file changed, 11 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/target-ppc/machine.c b/target-ppc/machine.c
>>> index 5d87ff6..62b9e94 100644
>>> --- a/target-ppc/machine.c
>>> +++ b/target-ppc/machine.c
>>> @@ -173,10 +173,12 @@ static int cpu_post_load(void *opaque, int version_id)
>>> target_ulong msr;
>>>
>>> /*
>>> - * We always ignore the source PVR. The user or management
>>> - * software has to take care of running QEMU in a compatible mode.
>>> + * If we're operating in compat mode, we should be ok as long as
>>> + * the destination supports the same compatiblity mode.
>>> + *
>>> + * Otherwise, however, we require that the destination has exactly
>>> + * the same CPU model as the source.
>>> */
>>> - env->spr[SPR_PVR] = env->spr_cb[SPR_PVR].default_value;
>>>
>>> #if defined(TARGET_PPC64)
>>> if (cpu->compat_pvr) {
>>> @@ -188,8 +190,13 @@ static int cpu_post_load(void *opaque, int version_id)
>>> error_free(local_err);
>>> return -1;
>>> }
>>> - }
>>> + } else
>>> #endif
>>> + {
>>> + if (env->spr[SPR_PVR] != env->spr_cb[SPR_PVR].default_value) {
>>> + return -1;
>>> + }
>>> + }
>>
>> This should break migration from host with PVR=004d0200 to host with
>> PVR=004d0201, what is the benefit of such limitation?
>
> There probably isn't one. But the point is it also blocks migration
> from a host with PVR=004B0201 (POWER8) to one with PVR=00201400
> (403GCX) and *that* has a clear benefit. I don't see a way to block
> the second without the first, except by creating a huge compatibility
> matrix table, which would require inordinate amounts of time to
> research carefully.This is pcc->pvr_match() for this purpose. -- Alexey
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