Linux Virtualization - Jun 2020 - [PATCH v3 1/1] s390: virtio: let arch accept devices without IOMMU feature

On 2020-06-19 11:20, Cornelia Huck wrote:
> On Thu, 18 Jun 2020 00:29:56 +0200
> Halil Pasic <pasic at linux.ibm.com> wrote:
> 
>> On Wed, 17 Jun 2020 12:43:57 +0200
>> Pierre Morel <pmorel at linux.ibm.com> wrote:
...
>>
>> But since this can be rewritten any time, let's go with the option
>> people already agree with, instead of more discussion.
> 
> Yes, there's nothing wrong with the patch as-is.
> 
> Acked-by: Cornelia Huck <cohuck at redhat.com>
Thanks,

> 
> Which tree should this go through? Virtio? s390? >
>>
>> Just another question. Do we want this backported? Do we need cc
stable?
> 
> It does change behaviour of virtio-ccw devices; but then, it only
> fences off configurations that would not have worked anyway.
> Distributions should probably pick this; but I do not consider it
> strictly a "fix" (more a mitigation for broken configurations),
so I'm
> not sure whether stable applies.
> 
>> [..]
>>
>>
>>>   int virtio_finalize_features(struct virtio_device *dev)
>>>   {
>>>   	int ret = dev->config->finalize_features(dev);
>>> @@ -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");
>>
>> 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.

Regards,
Pierre

-- 
Pierre Morel
IBM Lab Boeblingen

On Mon, 29 Jun 2020 15:14:04 +0200
Pierre Morel <pmorel at linux.ibm.com> wrote:
> On 2020-06-19 11:20, Cornelia Huck wrote:
> > On Thu, 18 Jun 2020 00:29:56 +0200
> > Halil Pasic <pasic at linux.ibm.com> wrote:
> >   
> >> On Wed, 17 Jun 2020 12:43:57 +0200
> >> Pierre Morel <pmorel at linux.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.]
> >>
> >> 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.

On 2020-06-29 15:44, Cornelia Huck wrote:
> On Mon, 29 Jun 2020 15:14:04 +0200
> Pierre Morel <pmorel at linux.ibm.com> wrote:
> 
>> On 2020-06-19 11:20, Cornelia Huck wrote:
>>> On Thu, 18 Jun 2020 00:29:56 +0200
>>> Halil Pasic <pasic at linux.ibm.com> wrote:
>>>    
>>>> On Wed, 17 Jun 2020 12:43:57 +0200
>>>> Pierre Morel <pmorel at linux.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