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

[Yi Liu]

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@xxxxxxxxx>
> > > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > > ---
> > >   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