linux-kernel - Re: [PATCH v2 4/7] s390/physmem_info: query diag500(STORAGE LIMIT) to support QEMU/KVM memory devices

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Message-ID: <20241016123702.04688e2d.pasic@linux.ibm.com>
Date: Wed, 16 Oct 2024 12:37:02 +0200
From: Halil Pasic <pasic@...ux.ibm.com>
To: Eric Farman <farman@...ux.ibm.com>
Cc: Heiko Carstens <hca@...ux.ibm.com>, David Hildenbrand
 <david@...hat.com>,
        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>,
        Mario
 Casquero <mcasquer@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH v2 4/7] s390/physmem_info: query diag500(STORAGE LIMIT)
 to support QEMU/KVM memory devices

On Tue, 15 Oct 2024 11:01:44 -0400
Eric Farman <farman@...ux.ibm.com> wrote:

> > +		  [subcode] "i" (DIAG500_SC_STOR_LIMIT)
> > +		: "memory", "1", "2");
> > +	if (!storage_limit)
> > +		return -EINVAL;
> > +	/* Convert inclusive end to exclusive end */
> > +	*max_physmem_end = storage_limit + 1;
> >  	return 0;
> >  }
> >  
> >   
> 
> I like the idea of a defined constant here instead of hardcoded, but maybe it should be placed
> somewhere in include/uapi so that QEMU can pick it up with update-linux-headers.sh and be in sync
> with the kernel, instead of just an equivalent definition in [1] ?
> 
> [1] https://lore.kernel.org/qemu-devel/20241008105455.2302628-8-david@redhat.com/

I think it is fine to have equivalent definitions. This is more or less
an ISA thing we are introducing here. And IMHO it would be fine to have
such a definition even if the emulator was supposed to run on an OS that
is not Linux and without without KVM.

Regards,
Halil