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

From: Cédric Le Goater
Subject: Re: [Qemu-ppc] [PATCH v5 08/36] ppc/xive: introduce a simplified XIVE presenter
Date: Thu, 29 Nov 2018 18:51:53 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0

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, 


>> 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

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().  


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


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



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