Re: [PATCH 1/1] iommu/vt-d: Move PCI PASID enablement to probe path

From: Baolu Lu
Date: Mon Aug 19 2024 - 03:09:55 EST


On 2024/8/19 14:34, Vasant Hegde wrote:
On 8/16/2024 6:39 PM, Baolu Lu wrote:
On 2024/8/16 20:16, Vasant Hegde wrote:
On 8/16/2024 4:19 PM, Lu Baolu wrote:
Currently, PCI PASID is enabled alongside PCI ATS when an iommu domain is
attached to the device and disabled when the device transitions to block
translation mode. This approach is inappropriate as PCI PASID is a device
feature independent of the type of the attached domain.
Reading through other thread, I thought we want to enable both PASID and PRI in
device probe path. Did I miss something?
PRI is different. PRI should be enabled when the first iopf-capable
domain is attached to device or its PASID, and disabled when the last
such domain is detached.
Right. That's what AMD driver also does (We enable it when we attach IOPF
capable domain). But looking into pci_enable_pri() :


202 /*
203 * VFs must not implement the PRI Capability. If their PF
204 * implements PRI, it is shared by the VFs, so if the PF PRI is
205 * enabled, it is also enabled for the VF.
206 */
207 if (pdev->is_virtfn) {
208 if (pci_physfn(pdev)->pri_enabled)
209 return 0;
210 return -EINVAL;
211 }
212


If we try to enable PRI for VF without first enabling it in PF it will fail right?

Now if PF is attached to non-IOPF capable domain (like in AMD case attaching to
domain with V1 page table) and we try to attach VF to IOPF capable domain (say
AMD v2 page table -OR- nested domain) it will fail right?

Yeah! So, the iommu driver should basically control the PRI switch on
the PF whenever someone wants to use it on a VF.

We could simplify things by turning on PRI for the whole PF when the
first iopf-capable domain is attached to a VF. Then, we'd only turn it
off once all VFs have such domains detached.

Thanks,
baolu
Yeah, so the iommu driver should flip the PRI switch on the PF whenever
someone wants to turn it on for its VF.

We could change things up so that when the first iopf-capable domain is attached to any VF or PF, we turn on PRI for the whole device. Then, we
turn it off when every VF and PF have such domains detached.