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

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Message-ID: <580e0907-cd58-45d3-8ba8-7344e5644354@intel.com>
Date: Mon, 19 Aug 2024 12:51:08 +0800
From: Yi Liu <yi.l.liu@...el.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>
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

On 2024/8/19 11:34, Baolu Lu wrote:
> On 2024/8/19 11:14, Yi Liu wrote:
>> On 2024/8/16 18:49, 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.
>>>
>>> Enable PCI PASID during the IOMMU device probe and disables it during the
>>> release path.
>>>
>>> Suggested-by: Yi Liu <yi.l.liu@...el.com>
>>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>>> ---
>>>   drivers/iommu/intel/iommu.c | 27 +++++++++++++--------------
>>>   1 file changed, 13 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>>> index 9ff8b83c19a3..5a8080c71b04 100644
>>> --- a/drivers/iommu/intel/iommu.c
>>> +++ b/drivers/iommu/intel/iommu.c
>>> @@ -1322,15 +1322,6 @@ static void iommu_enable_pci_caps(struct 
>>> device_domain_info *info)
>>>           return;
>>>       pdev = to_pci_dev(info->dev);
>>> -
>>> -    /* The PCIe spec, in its wisdom, declares that the behaviour of
>>> -       the device if you enable PASID support after ATS support is
>>> -       undefined. So always enable PASID support on devices which
>>> -       have it, even if we can't yet know if we're ever going to
>>> -       use it. */
>>> -    if (info->pasid_supported && !pci_enable_pasid(pdev, 
>>> info->pasid_supported & ~1))
>>> -        info->pasid_enabled = 1;
>>> -
>>>       if (info->ats_supported && pci_ats_page_aligned(pdev) &&
>>>           !pci_enable_ats(pdev, VTD_PAGE_SHIFT)) {
>>>           info->ats_enabled = 1;
>>> @@ -1352,11 +1343,6 @@ static void iommu_disable_pci_caps(struct 
>>> device_domain_info *info)
>>>           info->ats_enabled = 0;
>>>           domain_update_iotlb(info->domain);
>>>       }
>>> -
>>> -    if (info->pasid_enabled) {
>>> -        pci_disable_pasid(pdev);
>>> -        info->pasid_enabled = 0;
>>> -    }
>>>   }
>>>   static void intel_flush_iotlb_all(struct iommu_domain *domain)
>>> @@ -4110,6 +4096,16 @@ static struct iommu_device 
>>> *intel_iommu_probe_device(struct device *dev)
>>>           }
>>>       }
>>> +    /*
>>> +     * The PCIe spec, in its wisdom, declares that the behaviour of the
>>> +     * device is undefined if you enable PASID support after ATS support.
>>> +     * So always enable PASID support on devices which have it, even if
>>> +     * we can't yet know if we're ever going to use it.
>>> +     */
>>> +    if (info->pasid_supported &&
>>> +        !pci_enable_pasid(pdev, info->pasid_supported & ~1))
>>> +        info->pasid_enabled = 1;
>>> +
>>>       intel_iommu_debugfs_create_dev(info);
>>>       return &iommu->iommu;
>>> @@ -4128,6 +4124,9 @@ static void intel_iommu_release_device(struct 
>>> device *dev)
>>>       struct device_domain_info *info = dev_iommu_priv_get(dev);
>>>       struct intel_iommu *iommu = info->iommu;
>>> +    if (info->pasid_enabled)
>>> +        pci_disable_pasid(to_pci_dev(dev));
>>> +
>>
>> would it make sense to move this behind the
>> intel_iommu_debugfs_remove_dev(info)? This seems to mirror the order of the
>> intel_iommu_probe_device(). Or you may set info->pasid_enabled to 0 in case
>> of any code uses it before info is freed if keeping this order. Otherwise,
>> lgtm. thanks for the quick action. 🙂
> 
> The info->pasid_enabled change should not impact the behavior of
> intel_iommu_debugfs_remove_dev(), and I didn't find any issue during my
> test.
> 
> Anyway, to make it more consistent with previous behavior, maybe I could
> move the part where we turn on/off pasid to the end of the probe and the
> start of the release.

yeah, this looks ok. And you may consider to clear info->pasid_enabled
when it's disabled. I guess it does not affect device_rbtree_remove(),
intel_pasid_teardown_sm_context(), intel_pasid_free_table() nor the
intel_iommu_debugfs_remove_dev(), but good to clear it as it to
reflect the status.:)

> Additional change likes below?
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 5a8080c71b04..76b317f1d1de 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4096,6 +4096,8 @@ static struct iommu_device 
> *intel_iommu_probe_device(struct device *dev)
>                  }
>          }
> 
> +       intel_iommu_debugfs_create_dev(info);
> +
>          /*
>           * The PCIe spec, in its wisdom, declares that the behaviour of the
>           * device is undefined if you enable PASID support after ATS support.
> @@ -4106,8 +4108,6 @@ static struct iommu_device 
> *intel_iommu_probe_device(struct device *dev)
>              !pci_enable_pasid(pdev, info->pasid_supported & ~1))
>                  info->pasid_enabled = 1;
> 
> -       intel_iommu_debugfs_create_dev(info);
> -
>          return &iommu->iommu;
>   free_table:
>          intel_pasid_free_table(dev);
> 
> Thanks,
> baolu

-- 
Regards,
Yi Liu