linux-kernel - Re: [PATCH v3 2/2] iommu/vt-d: don's issue devTLB flush request when device is disconnected

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Message-ID: <f7dfdec4-ec52-44b0-9e04-bdcc3af2ba25@linux.intel.com>
Date: Tue, 19 Dec 2023 14:57:22 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Ethan Zhao <haifeng.zhao@...ux.intel.com>, bhelgaas@...gle.com,
 dwmw2@...radead.org, will@...nel.org, robin.murphy@....com, lukas@...ner.de
Cc: baolu.lu@...ux.intel.com, linux-pci@...r.kernel.org,
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] iommu/vt-d: don's issue devTLB flush request when
 device is disconnected

On 2023/12/19 14:49, Ethan Zhao wrote:
>>> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
>>> index 74e8e4c17e81..182eb5df244d 100644
>>> --- a/drivers/iommu/intel/pasid.c
>>> +++ b/drivers/iommu/intel/pasid.c
>>> @@ -476,6 +476,23 @@ devtlb_invalidation_with_pasid(struct 
>>> intel_iommu *iommu,
>>>   {
>>>       struct device_domain_info *info;
>>>       u16 sid, qdep, pfsid;
>>> +    struct pci_dev *pdev;
>>> +
>>> +    pdev = to_pci_dev(dev);
>>> +    if (!pdev)
>>> +        return;
>>> +
>>> +    /*
>>> +     * If endpoint device's link was brough down by user's pci 
>>> configuration
>>> +     * access to it's hotplug capable slot link control register, as 
>>> sequence
>>> +     * response for DLLSC, pciehp_ist() will set the device 
>>> error_state to
>>> +     * pci_channel_io_perm_failure. Checking device's state here to 
>>> avoid
>>> +     * issuing meaningless devTLB flush request to it, that might 
>>> cause lockup
>>> +     * warning or deadlock because too long time waiting in 
>>> interrupt context.
>>> +     */
>>> +
>>> +    if (pci_dev_is_disconnected(pdev))
>>> +        return;
>>>         info = dev_iommu_priv_get(dev);
>>>       if (!info || !info->ats_enabled)
>>
>> It's likely better to check the device status after verifying
>> ats_enabled. How about below change?
>>
>> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
>> index 74e8e4c17e81..fa19c6cdfd8b 100644
>> --- a/drivers/iommu/intel/pasid.c
>> +++ b/drivers/iommu/intel/pasid.c
>> @@ -481,6 +481,9 @@ devtlb_invalidation_with_pasid(struct intel_iommu 
>> *iommu,
>>         if (!info || !info->ats_enabled)
>>                 return;
>>
>> +       if (pci_dev_is_disconnected(to_pci_dev(dev)))
> 
> I like this kind of simplicity, but rationalist always brings me back to 
> the no-error(ugly)
> 
> style.  🙂

The rational is that Intel IOMMU driver only supports PCI ATS. So if
device is marked as ATS supported, then it must be a PCI device.
Therefore, it's safe to convert it to pci_device with to_pci_dev().

If you move this up before ATS checking, then you need to check
dev_is_pci().

Best regards,
baolu