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

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Message-ID: <eb58cbad-1f28-480b-9b46-76d6d0c8b62b@linux.intel.com>
Date: Mon, 19 Aug 2024 13:15:45 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Yi Liu <yi.l.liu@...el.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: baolu.lu@...ux.intel.com, 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 12:51, Yi Liu wrote:
> 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.:)

Done.

Thanks,
baolu