linux-kernel - Re: [PATCH 0/2] iommu: Make pasid array per device

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Message-ID: <ZMplBfgSb8Hh9jLt@ziepe.ca>
Date:   Wed, 2 Aug 2023 11:15:33 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Tian <kevin.tian@...el.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Nicolin Chen <nicolinc@...dia.com>,
        Yi Liu <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        iommu@...ts.linux.dev, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] iommu: Make pasid array per device

On Tue, Aug 01, 2023 at 02:31:23PM +0800, Lu Baolu wrote:
> The PCI PASID enabling interface guarantees that the address space used
> by each PASID is unique. This is achieved by checking that the PCI ACS
> path is enabled for the device. If the path is not enabled, then the
> PASID feature cannot be used.
> 
>     if (!pci_acs_path_enabled(pdev, NULL, PCI_ACS_RR | PCI_ACS_UF))
>             return -EINVAL;
> 
> The PASID array is not an attribute of the IOMMU group. It is more
> natural to store the PASID array in the per-device IOMMU data. This
> makes the code clearer and easier to understand. No functional changes
> are intended.

Is there a reason to do this?

*PCI* requires the ACS/etc because PCI kind of messed up how switches
handled PASID so PASID doesn't work otherwise.

But there is nothing that says other bus type can't have working
(non-PCI) PASID and still have device isolation issues.

So unless there is a really strong reason to do this we should keep
the PASID list in the group just like the domain.

Jason