Re: [PATCH RFC] KVM: PPC: Book3S HV: Reserve POWER8 space in get/set_one_reg

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On Sat, Aug 31, 2013 at 12:01 AM, Alexander Graf <agraf@xxxxxxx> wrote:
>
> On 30.08.2013, at 08:09, Michael Neuling wrote:
>
>> Alex,
>>
>> This reserves space in get/set_one_reg ioctl for the extra guest state
>> needed for POWER8.  It doesn't implement these at all, it just reserves
>> them so that the ABI is defined now.
>>
>> A few things to note here:
>>
>> - POWER8 has 6 PMCs and an additional 2 SPMCs for the supervisor.  Here
>>  I'm storing these 2 SPMCs in PMC7/8.
>
> Is this safe to do? Are we guaranteed that POWER9 or POWER10 doesn't introduce a real PMC7?

Good point.  I'll change it.

>
>> - This add *a lot* state for transactional memory.  TM suspend mode,
>>  this is unavoidable, you can't simply roll back all transactions and
>>  store only the checkpointed state.  I've added this all to
>>  get/set_one_reg (including GPRs) rather than creating a new ioctl
>>  which returns a struct kvm_regs like KVM_GET_REGS does.  This means we
>>  if we need to extract the TM state, we are going to need a bucket load
>>  of IOCTLs.  Hopefully most of the time this will not be needed as we
>>  can look at the MSR to see if TM is active and only grab them when
>>  needed.
>
> If we find this to be a performance issue, we can always add a new ioctl that allows multiple ONE_REG accesses at a time. The only reason we don't have that yet is that bulk one_reg access hasn't happened in any performance critical path so far.

Ok.

>
>>
>> - The TM state is offset bu 0x1000.  Other than being bigger than the
>>  SPR space, it's fairly arbitrarily chose.
>>
>> - For TM, I've done away with VMX and FP and created a single 64x128 bit
>>  VSX register space.
>>
>> Alex: I'll add the documentation Documentation/virtual/kvm/api.txt if
>> you're happy with all this.
>
> Looks perfectly reasonable to me :).

Thanks.  I'll repost.

Mikey
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