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Date: Tue, 28 May 2019 16:56:27 +0200
From: Cornelia Huck <cohuck@redhat.com>
Subject: Re: [PATCH v2 8/8] virtio/s390: make airq summary indicators DMA
Message-ID: <20190528165627.76da557a.cohuck@redhat.com>
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        <20190528163342.335eea0b.pasic@linux.ibm.com>
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To: Halil Pasic <pasic@linux.ibm.com>
Cc: Michael Mueller <mimu@linux.ibm.com>, KVM Mailing List <kvm@vger.kernel.org>, Linux-S390 Mailing List <linux-s390@vger.kernel.org>, Sebastian Ott <sebott@linux.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, virtualization@lists.linux-foundation.org, "Michael S . Tsirkin" <mst@redhat.com>, Christoph Hellwig <hch@infradead.org>, Thomas Huth <thuth@redhat.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Viktor Mihajlovski <mihajlov@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, Janosch Frank <frankja@linux.ibm.com>, Claudio Imbrenda <imbrenda@linux.ibm.com>, Farhan Ali <alifm@linux.ibm.com>, Eric Farman <farman@linux.ibm.com>, Pierre Morel <pmorel@linux.ibm.com>
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On Tue, 28 May 2019 16:33:42 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Mon, 27 May 2019 14:00:18 +0200
> Cornelia Huck <cohuck@redhat.com> wrote:
> 
> > On Thu, 23 May 2019 18:22:09 +0200
> > Michael Mueller <mimu@linux.ibm.com> wrote:
> >   
> > > From: Halil Pasic <pasic@linux.ibm.com>
> > > 
> > > Hypervisor needs to interact with the summary indicators, so these
> > > need to be DMA memory as well (at least for protected virtualization
> > > guests).
> > > 
> > > Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
> > > ---
> > >  drivers/s390/virtio/virtio_ccw.c | 22 +++++++++++++++-------
> > >  1 file changed, 15 insertions(+), 7 deletions(-)  
> > 
> > (...)
> >   
> > > @@ -1501,6 +1508,7 @@ static int __init virtio_ccw_init(void)
> > >  {
> > >  	/* parse no_auto string before we do anything further */
> > >  	no_auto_parse();
> > > +	summary_indicators = cio_dma_zalloc(MAX_AIRQ_AREAS);  
> > 
> > What happens if this fails?  
> 
> Bad things could happen!
> 
> How about adding
> 
> if (!summary_indicators)
> 	virtio_ccw_use_airq = 0; /* fall back to classic */
> 
> ?
> 
> Since it ain't very likely to happen, we could also just fail
> virtio_ccw_init() with -ENOMEM.

How high are the chances of things working if we fail to allocate here?
Returning with -ENOMEM is probably the more reasonable approach here.