linux-kernel - Re: [PATCH v3 1/1] s390: virtio: let arch accept devices without IOMMU feature

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Date:   Mon, 29 Jun 2020 18:10:02 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     Halil Pasic <pasic@...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@...son.dropbear.id.au, linuxram@...ibm.com,
        heiko.carstens@...ibm.com, gor@...ux.ibm.com
Subject: Re: [PATCH v3 1/1] s390: virtio: let arch accept devices without
 IOMMU feature



On 2020-06-29 15:44, Cornelia Huck wrote:
> On Mon, 29 Jun 2020 15:14:04 +0200
> Pierre Morel <pmorel@...ux.ibm.com> wrote:
> 
>> On 2020-06-19 11:20, Cornelia Huck wrote:
>>> On Thu, 18 Jun 2020 00:29:56 +0200
>>> Halil Pasic <pasic@...ux.ibm.com> wrote:
>>>    
>>>> On Wed, 17 Jun 2020 12:43:57 +0200
>>>> Pierre Morel <pmorel@...ux.ibm.com> wrote:
> 
>>>>> @@ -179,6 +194,13 @@ int virtio_finalize_features(struct virtio_device *dev)
>>>>>    	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
>>>>>    		return 0;
>>>>>    
>>>>> +	if (arch_needs_virtio_iommu_platform(dev) &&
>>>>> +		!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
>>>>> +		dev_warn(&dev->dev,
>>>>> +			 "virtio: device must provide VIRTIO_F_IOMMU_PLATFORM\n");
> 
> [Side note: wasn't there a patch renaming this bit on the list? I think
> this name is only kept for userspace compat.]

Sorry, I do not understand what you expect from me.
On which mailing list you think there is a patch on?

> 
>>>>
>>>> I'm not sure, divulging the current Linux name of this feature bit is a
>>>> good idea, but if everybody else is fine with this, I don't care that
>>>
>>> Not sure if that feature name will ever change, as it is exported in
>>> headers. At most, we might want to add the new ACCESS_PLATFORM define
>>> and keep the old one, but that would still mean some churn.
>>>    
>>>> much. An alternative would be:
>>>> "virtio: device falsely claims to have full access to the memory,
>>>> aborting the device"
>>>
>>> "virtio: device does not work with limited memory access" ?
>>>
>>> But no issue with keeping the current message.
>>>    
>>
>> If it is OK, I would like to specify that the arch is responsible to
>> accept or not the device.
>> The reason why the device is not accepted without IOMMU_PLATFORM is arch
>> specific.
> 
> Hm, I'd think the reason is always the same (the device cannot access
> the memory directly), just the way to figure out whether that is the
> case or not is arch-specific, as with so many other things. No real
> need to go into detail here, I think.
> 

As you like, so I rename the subject to:
"virtio: device does not work with limited memory access"

Regards,

Pierre


-- 
Pierre Morel
IBM Lab Boeblingen