On 11/11/2024 12:32, Joao Martins wrote:
depends on VIRTIO_PCI
select VFIO_PCI_CORE
select IOMMUFD_DRIVER
IIUC, this is not a dependency, the device will just lack dirty page
tracking with either the type1 backend or when using iommufd when the
IOMMU hardware doesn't have dirty page tracking, therefore all VM
memory is perpetually dirty. Do I have that right?
IOMMUFD_DRIVER is selected to utilize the dirty tracking functionality of IOMMU.
Therefore, this is a select option rather than a dependency, similar to how the
pds and mlx5 VFIO drivers handle it in their Kconfig files.
Yishai, I think Alex is right here.
'select IOMMUFD_DRIVER' is more for VF dirty trackers where it uses the same
helpers as IOMMUFD does for dirty tracking. But it's definitely not signaling
intent for 'IOMMU dirty tracking' but rather 'VF dirty tracking'
I see, please see below.
If you want to tie in to IOMMU dirty tracking you probably want to do:
'select IOMMUFD'
Looking at the below Kconfig(s) for AMD/INTEL_IOMMU [1], we can see that
if IOMMUFD is set IOMMFD_DRIVER is selected.
From that we can assume that to have 'IOMMU dirty tracking' the
IOMMFD_DRIVER is finally needed/selected, right ?
So you are saying that it's redundant in the vfio/virtio driver as it
will be selected down the road once needed ?
[1]
https://elixir.bootlin.com/linux/v6.12-rc6/source/drivers/iommu/intel/Kconfig#L17
https://elixir.bootlin.com/linux/v6.12-rc6/source/drivers/iommu/amd/Kconfig#L16
But that is a big hammer, as you also need the VFIO_DEVICE_CDEV kconfig selected
as well and probably more.
I agree, we didn't plan to add those dependencies.
Perhaps best to do like qat/hisilicon drivers and letting the user optionally
pick it. Migration is anyways disabled when using type1 (unless you force it,
and it then it does the perpectual dirty trick).
I can drop it in V3 if we all agree that it's not really needed here.
Thanks,
Yishai
