linux-kernel - Re: [PATCH v2 2/7] Documentation: s390-diag.rst: make diag500 a generic KVM hypercall

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Message-ID: <8e39522c-2853-4d1f-b5ec-64fabcca968b@redhat.com>
Date: Tue, 15 Oct 2024 10:16:20 +0200
From: David Hildenbrand <david@...hat.com>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
 linux-doc@...r.kernel.org, kvm@...r.kernel.org,
 Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev
 <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Thomas Huth <thuth@...hat.com>,
 Cornelia Huck <cohuck@...hat.com>, Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>,
 "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>,
 Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH v2 2/7] Documentation: s390-diag.rst: make diag500 a
 generic KVM hypercall

On 15.10.24 10:12, Heiko Carstens wrote:
> On Mon, Oct 14, 2024 at 09:35:27PM +0200, David Hildenbrand wrote:
>> On 14.10.24 20:04, Heiko Carstens wrote:
>>> On Mon, Oct 14, 2024 at 04:46:14PM +0200, David Hildenbrand wrote:
>>> If so, it would be nice to document that too; but that is not
>>> necessarily your problem.
>>
>> I can squash:
>>
>> diff --git a/Documentation/virt/kvm/s390/s390-diag.rst b/Documentation/virt/kvm/s390/s390-diag.rst
>> index d9b7c6cbc99e..48a326d41cc0 100644
>> --- a/Documentation/virt/kvm/s390/s390-diag.rst
>> +++ b/Documentation/virt/kvm/s390/s390-diag.rst
>> @@ -50,6 +50,9 @@ Upon completion of the DIAGNOSE instruction, general register 2 contains
>>   the function's return code, which is either a return code or a subcode
>>   specific value.
>> +If the specified subfunction is not supported, a SPECIFICATION exception
>> +will be triggered.
>> +
> 
> Looks good. Thanks!
> 
>>> I guess we won't see too many new diag 500 subcodes, or would it make
>>> sense to implement some query subcode?
>>
>> In the context of STORAGE LIMIT, a "query" subfunction is not really beneficial:
>>
>> it's either one invocation of "query", conditionally followed by one invocation of "STORAGE LIMIT"
>> vs. one invocation of "STORAGE LIMIT".
>>
>> Once there might be a bunch of other subfunctions, a "query" might make more sense.
> 
> "If only there would be a query subcode available, so that the program
> check handling would not be necessary; but in particular my new subcode
> is not worth adding it" :)
> 
> Anyway, I do not care too much.
> 

Okay, I see your point: it would allow for removing the program check 
handling from the STORAGE LIMIT invocation.

... if only we wouldn't need the exact same program check handling for 
the new query subfunction :P

-- 
Cheers,

David / dhildenb