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

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Message-ID: <511f140b-2792-47b0-b366-cbbad6e80239@intel.com>
Date: Mon, 19 Aug 2024 11:14:24 +0800
From: Yi Liu <yi.l.liu@...el.com>
To: Lu Baolu <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 2024/8/16 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. :)

Reviewed-by: Yi Liu <yi.l.liu@...el.com>

>   	mutex_lock(&iommu->iopf_lock);
>   	if (dev_is_pci(dev) && pci_ats_supported(to_pci_dev(dev)))
>   		device_rbtree_remove(info);

-- 
Regards,
Yi Liu