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

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Message-ID: <2050b790-4d88-4e16-8af8-3bde759d5430@redhat.com>
Date: Tue, 15 Oct 2024 10:48:20 +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 10:46, Heiko Carstens wrote:
> On Tue, Oct 15, 2024 at 10:32:43AM +0200, David Hildenbrand wrote:
>> On 15.10.24 10:21, Heiko Carstens wrote:
>>> On Tue, Oct 15, 2024 at 10:16:20AM +0200, David Hildenbrand wrote:
>>>> 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:
>>>>> "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
>>>
>>> Yeah yeah, but I think you got that this might help in the future.
>>
>> Right. Adding it later also doesn't quite help to get rid of the checks
>> here, because some user space might implement STORAGE LIMIT without QUERY.
> 
> This would only help if the diag500 documentation would state that
> implementation of the QUERY subcode is mandatory. That is: for every
> new subcode larger than the QUERY subcode QUERY must also exist.
> 
> That way we only would have to implement program check handling once,
> if a program check happens on QUERY none of the newer subcodes is
> available, otherwise the return value would indicate that.
> 
> Otherwise this whole excercise would be pointless.

Yes, that would be the idea.

-- 
Cheers,

David / dhildenb