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From: Laurent Vivier <lvivier@redhat.com>
Message-ID: <4e667a79-68b7-4cf1-994c-b72ee738e0a6@redhat.com>
Date: Tue, 18 Dec 2018 11:57:28 +0100
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Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH] spapr: Add H-Call
 H_HOME_NODE_ASSOCIATIVITY
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To: Greg Kurz <groug@kaod.org>
Cc: David Gibson <david@gibson.dropbear.id.au>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, qemu-ppc@nongnu.org, qemu-devel@nongnu.org

On 18/12/2018 11:50, Greg Kurz wrote:
> On Tue, 18 Dec 2018 11:00:01 +0100
> Laurent Vivier <lvivier@redhat.com> wrote:
> 
>> On 18/12/2018 10:23, Greg Kurz wrote:
>>> On Tue, 18 Dec 2018 08:50:00 +0100
...
>>> Also, even if linux only seems to call this with 0x1, this is a
>>> limitation from a LoPAPR standpoint. Not sure H_PARAMETER is the
>>> appropriate return value if flags is 0x2 since the guest did
>>> nothing wrong... I'd rather return H_FUNCTION in this case.  
>>
>> The doc says:
>>
>>   H_Function:  The function is not supported
>>   H_Parameter: Unsupported flag parameter value
>>
>> in that case function is supported but not the flag, so I think
>> H_PARAMETER is a better choice.
>>
> 
> Well... neither LoPAPR, nor IBM confidential PAPR+ do say anything
> about partial support for this hcall. If the guest was to use the
> flags == 0x2 variant, eg, some closed-source OS supporting PAPR,
> it could be legitimately confused to get an H_PARAMETER error when
> passing supposedly valid parameters... how to cope with that ?
> On the other hand, if QEMU cannot honor the flags == 0x2 variant
> and returns H_FUNCTION then the OS can recover since it is
> required by the specification.

You have certainly access to more information than I have, so I'll
change H_PARAMETER to H_FUNCTION.

Thanks,
Laurent