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

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Date:   Fri, 4 Aug 2023 10:20:28 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...pe.ca>,
        "Tian, Kevin" <kevin.tian@...el.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Nicolin Chen <nicolinc@...dia.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] iommu: Make pasid array per device

On 2023/8/3 23:18, Jason Gunthorpe wrote:
> On Thu, Aug 03, 2023 at 12:44:03AM +0000, Tian, Kevin wrote:
>>> From: Jason Gunthorpe<jgg@...pe.ca>
>>> Sent: Wednesday, August 2, 2023 10:16 PM
>>>
>>> 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.
>>>
>> this comes from the consensus in [1].
>>
>> [1]https://lore.kernel.org/linux-iommu/ZAcyEzN4102gPsWC@nvidia.com/
> That consensus was that we don't have PASID support if there is
> multi-device groups, at least in iommufd.. That makes sense. If we
> want to change the core code to enforce this that also makes sense

In my initial plan, I had a third patch that would have enforced single-
device groups for PASID interfaces in the core. But I ultimately dropped
it because it is the fact for PCI devices, but I am not sure about other
buses although perhaps there is none.

> But this series is just moving the array?

So I took the first step by moving the pasid_array from iommu group to
the device. :-)

Best regards,
baolu