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

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Message-ID: <e130c5e7-40e5-40a8-eac3-c2d17c90ee7b@linux.ibm.com>
Date:   Tue, 16 Jun 2020 15:41:20 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>
Cc:     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 2020-06-16 14:17, Cornelia Huck wrote:
> 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.
> 

what about returning -ENODEV and add a dedicated warning here?

-- 
Pierre Morel
IBM Lab Boeblingen