linux-kernel - Re: [PATCH v2 1/1] s390: virtio: let arch accept devices without IOMMU feature

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Date:   Tue, 16 Jun 2020 14:17:44 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     Pierre Morel <pmorel@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        borntraeger@...ibm.com, frankja@...ux.ibm.com, mst@...hat.com,
        jasowang@...hat.com, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, thomas.lendacky@....com,
        David Gibson <david@...son.dropbear.id.au>,
        Ram Pai <linuxram@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH v2 1/1] s390: virtio: let arch accept devices without
 IOMMU feature

On Tue, 16 Jun 2020 13:57:26 +0200
Halil Pasic <pasic@...ux.ibm.com> wrote:

> On Tue, 16 Jun 2020 12:52:50 +0200
> Pierre Morel <pmorel@...ux.ibm.com> wrote:
> 
> > >>   int virtio_finalize_features(struct virtio_device *dev)
> > >>   {
> > >>   	int ret = dev->config->finalize_features(dev);
> > >> @@ -179,6 +184,10 @@ int virtio_finalize_features(struct virtio_device *dev)
> > >>   	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
> > >>   		return 0;
> > >>   
> > >> +	if (arch_needs_iommu_platform(dev) &&
> > >> +		!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM))
> > >> +		return -EIO;
> > >> +    
> > > 
> > > Why EIO?    
> > 
> > Because I/O can not occur correctly?
> > I am open to suggestions.  
> 
> We use -ENODEV if feature when the device rejects the features we
> tried to negotiate (see virtio_finalize_features()) and -EINVAL when
> the F_VERSION_1 and the virtio-ccw revision ain't coherent (in
> virtio_ccw_finalize_features()). Any of those seems more fitting
> that EIO to me. BTW does the error code itself matter in any way,
> or is it just OK vs some error?

If I haven't lost my way, we end up in the driver core probe failure
handling; we probably should do -ENODEV if we just want probing to fail
and -EINVAL or -EIO if we want the code to moan.