Re: [RFC PATCH 03/10] iommu/vt-d: Allocate groups for mediated devices

[Lu Baolu <baolu.lu@linux.intel.com>]

Hi Jean,

Pull Kevin in. Not sure why he was removed from cc list.

On 07/24/2018 07:30 PM, Jean-Philippe Brucker wrote:
> Hi Baolu,
>
> On 24/07/18 03:22, Lu Baolu wrote:
>> Hi,
>>
>> On 07/23/2018 12:44 PM, Liu, Yi L wrote:
>>>> From: Lu Baolu [mailto:baolu.lu@linux.intel.com]
>>>> Sent: Sunday, July 22, 2018 2:09 PM
>>>>
>>>> With the Intel IOMMU supporting PASID granularity isolation and protection, a
>>>> mediated device could be isolated and protected by an IOMMU unit. We need to
>>>> allocate a new group instead of a PCI group.
>>> Existing vfio mdev framework also allocates an iommu group for mediate device.
>>>
>>> mdev_probe()
>>>   |_ mdev_attach_iommu()
>>>        |_ iommu_group_alloc()
>> When external components ask iommu to allocate a group for a device,
>> it will call pci_device_group in Intel IOMMU driver's @device_group
>> callback. In another word, current Intel IOMMU driver doesn't aware
>> the mediated device and treat all devices as PCI ones. This patch
>> extends the @device_group call back to make it aware of a mediated
>> device.
> I agree that allocating two groups for an mdev seems strange, and in my
> opinion we shouldn't export the notion of mdev to IOMMU drivers.
> Otherwise each driver will have to add its own "dev_is_mdev()" special
> cases, which will get messy in the long run. Besides, the macro is
> currently private, and to be exported it should be wrapped in
> symbol_get/put(mdev_bus_type).

I agree with you.

It should be better if we can make it in a driver agnostic way.

>
> There is another way: as we're planning to add a generic pasid_alloc()
> function to the IOMMU API, the mdev module itself could allocate a
> default PASID for each mdev by calling pasid_alloc() on the mdev's
> parent, and then do map()/unmap() with that PASID. This way we don't
> have to add IOMMU ops to the mdev bus, everything can still be done
> using the ops of the parent. And IOMMU drivers "only" have to implement
> PASID ops, which will be reused by drivers other than mdev.

A quick question when I thinking about this is how to allocate a domain
for the mediated device who uses the default pasid for DMA transactions?

Best regards,
Lu Baolu

>
> The allocated PASID also needs to be installed into the parent device.
> If the mdev module knows the PASID, we can do that by adding
> set_pasid(mdev, pasid) and clear_pasid(mdev, pasid) operations to
> mdev_parent_ops.
>
> Thanks,
> Jean
>
>