Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 16 Jun 2020 13:57:26 +0200
From:   Halil Pasic <pasic@linux.ibm.com>
To:     Pierre Morel <pmorel@linux.ibm.com>
Cc:     linux-kernel@vger.kernel.org, borntraeger@de.ibm.com,
        frankja@linux.ibm.com, mst@redhat.com, jasowang@redhat.com,
        cohuck@redhat.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org,
        virtualization@lists.linux-foundation.org, thomas.lendacky@amd.com,
        David Gibson <david@gibson.dropbear.id.au>,
        Ram Pai <linuxram@us.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>
Subject: Re: [PATCH v2 1/1] s390: virtio: let arch accept devices without
 IOMMU feature
Message-ID: <20200616135726.04fa8314.pasic@linux.ibm.com>
In-Reply-To: <ef235cc9-9d4b-1247-c01a-9dd1c63f437c@linux.ibm.com>
References: <1592224764-1258-1-git-send-email-pmorel@linux.ibm.com>
        <1592224764-1258-2-git-send-email-pmorel@linux.ibm.com>
        <20200616115202.0285aa08.pasic@linux.ibm.com>
        <ef235cc9-9d4b-1247-c01a-9dd1c63f437c@linux.ibm.com>
Organization: IBM
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, 16 Jun 2020 12:52:50 +0200
Pierre Morel <pmorel@linux.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?

Regards,
Halil