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

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Message-ID: <635b24b7-632d-4046-b82e-6ac6976686c9@amd.com>
Date: Mon, 19 Aug 2024 12:04:09 +0530
From: Vasant Hegde <vasant.hegde@....com>
To: Baolu Lu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jason Gunthorpe <jgg@...pe.ca>, Kevin Tian <kevin.tian@...el.com>,
 Yi Liu <yi.l.liu@...el.com>
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/vt-d: Move PCI PASID enablement to probe path

Hi,


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?



-Vasant