Re: [Qemu-ppc] [PATCH v5 08/36] ppc/xive: introduce a simplified XIVE presenter

[Cédric Le Goater]

On 11/29/18 4:39 AM, Benjamin Herrenschmidt wrote:
> On Thu, 2018-11-29 at 11:47 +1100, David Gibson wrote:
>>
>> 1) read/write accessors which take a word number

ok for single word updates of the structures.

>> 2) A "get" accessor which copies the whole structure, 

ok

>> but "write"
>> accessor which takes a word number.  The asymmetry is a bit ugly, but
>> it's the non-atomic writeback of the whole structure which I'm most
>> uncomfortable with.

And, how would you make the update of the whole structure in RAM look 
"atomic" under QEMU ? 

> It shouldn't be a big deal though, there are HW facilities to access
> the structures "atomically" anyway, due to the caching done by the
> XIVE.

Are you suggesting that the PowerNV model should update the VPC, EQC, 
IVC in the VST accessors before updating the VSTs in RAM ?
>> 3) A map/unmap interface which gives you / releases a pointer to the
>> "live" structure.  For powernv that would become
>> address_space_map()/unmap().  

yes.

>> For PAPR it would just be reutn pointer  / no-op.

ok

I think I will introduce these handlers progressively in the patchset.

Thanks,

C.