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SubjectRe: [PATCH v8 7/9] vfio/mdev: Add iommu related member in mdev_device
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Hi Jason,

On 4/7/21 4:00 AM, Jason Gunthorpe wrote:
> On Mon, Mar 25, 2019 at 09:30:34AM +0800, Lu Baolu wrote:
>> A parent device might create different types of mediated
>> devices. For example, a mediated device could be created
>> by the parent device with full isolation and protection
>> provided by the IOMMU. One usage case could be found on
>> Intel platforms where a mediated device is an assignable
>> subset of a PCI, the DMA requests on behalf of it are all
>> tagged with a PASID. Since IOMMU supports PASID-granular
>> translations (scalable mode in VT-d 3.0), this mediated
>> device could be individually protected and isolated by an
>> IOMMU.
>>
>> This patch adds a new member in the struct mdev_device to
>> indicate that the mediated device represented by mdev could
>> be isolated and protected by attaching a domain to a device
>> represented by mdev->iommu_device. It also adds a helper to
>> add or set the iommu device.
>>
>> * mdev_device->iommu_device
>> - This, if set, indicates that the mediated device could
>> be fully isolated and protected by IOMMU via attaching
>> an iommu domain to this device. If empty, it indicates
>> using vendor defined isolation, hence bypass IOMMU.
>>
>> * mdev_set/get_iommu_device(dev, iommu_device)
>> - Set or get the iommu device which represents this mdev
>> in IOMMU's device scope. Drivers don't need to set the
>> iommu device if it uses vendor defined isolation.
>>
>> Cc: Ashok Raj <ashok.raj@intel.com>
>> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
>> Cc: Kevin Tian <kevin.tian@intel.com>
>> Cc: Liu Yi L <yi.l.liu@intel.com>
>> Suggested-by: Kevin Tian <kevin.tian@intel.com>
>> Suggested-by: Alex Williamson <alex.williamson@redhat.com>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> Reviewed-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
>> ---
>> drivers/vfio/mdev/mdev_core.c | 18 ++++++++++++++++++
>> drivers/vfio/mdev/mdev_private.h | 1 +
>> include/linux/mdev.h | 14 ++++++++++++++
>> 3 files changed, 33 insertions(+)
>>
>> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
>> index b96fedc77ee5..1b6435529166 100644
>> +++ b/drivers/vfio/mdev/mdev_core.c
>> @@ -390,6 +390,24 @@ int mdev_device_remove(struct device *dev, bool force_remove)
>> return 0;
>> }
>>
>> +int mdev_set_iommu_device(struct device *dev, struct device *iommu_device)
>> +{
>> + struct mdev_device *mdev = to_mdev_device(dev);
>> +
>> + mdev->iommu_device = iommu_device;
>> +
>> + return 0;
>> +}
>> +EXPORT_SYMBOL(mdev_set_iommu_device);
>
> I was looking at these functions when touching the mdev stuff and I
> have some concerns.
>
> 1) Please don't merge dead code. It is a year later and there is still
> no in-tree user for any of this. This is not our process. Even
> worse it was exported so it looks like this dead code is supporting
> out of tree modules.
>
> 2) Why is this like this? Every struct device already has a connection
> to the iommu layer and every mdev has a struct device all its own.
>
> Why did we need to add special 'if (mdev)' stuff all over the
> place? This smells like the same abuse Thomas
> and I pointed out for the interrupt domains.

I've ever tried to implement a bus iommu_ops for mdev devices.

https://lore.kernel.org/lkml/20201030045809.957927-1-baolu.lu@linux.intel.com/

Any comments?

Best regards,
baolu

>
> After my next series the mdev drivers will have direct access to
> the vfio_device. So an alternative to using the struct device, or
> adding 'if mdev' is to add an API to the vfio_device world to
> inject what iommu configuration is needed from that direction
> instead of trying to discover it from a struct device.
>
> 3) The vfio_bus_is_mdev() and related symbol_get() nonsense in
> drivers/vfio/vfio_iommu_type1.c has to go, for the same reasons
> it was not acceptable to do this for the interrupt side either.
>
> 4) It seems pretty clear to me this will be heavily impacted by the
> /dev/ioasid discussion. Please consider removing the dead code now.
>
> Basically, please fix this before trying to get idxd mdev merged as
> the first user.
>
> Jason
>

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