linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Fix RID2PASID setup failure

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Message-ID: <88295461-7cba-7c30-6b9e-63ee77e90295@linux.intel.com>
Date:   Tue, 21 Jun 2022 14:15:11 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        "Raj, Ashok" <ashok.raj@...el.com>
Cc:     baolu.lu@...ux.intel.com, "Qiang, Chenyi" <chenyi.qiang@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 1/1] iommu/vt-d: Fix RID2PASID setup failure

On 2022/6/21 13:48, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@...ux.intel.com>
>> Sent: Tuesday, June 21, 2022 12:28 PM
>>
>> On 2022/6/21 11:46, Tian, Kevin wrote:
>>>> From: Baolu Lu <baolu.lu@...ux.intel.com>
>>>> Sent: Tuesday, June 21, 2022 11:39 AM
>>>>
>>>> On 2022/6/21 10:54, Tian, Kevin wrote:
>>>>>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>>>>>> Sent: Monday, June 20, 2022 4:17 PM
>>>>>> @@ -2564,7 +2564,7 @@ static int domain_add_dev_info(struct
>>>>>> dmar_domain *domain, struct device *dev)
>>>>>>     			ret = intel_pasid_setup_second_level(iommu,
>>>>>> domain,
>>>>>>     					dev, PASID_RID2PASID);
>>>>>>     		spin_unlock_irqrestore(&iommu->lock, flags);
>>>>>> -		if (ret) {
>>>>>> +		if (ret && ret != -EBUSY) {
>>>>>>     			dev_err(dev, "Setup RID2PASID failed\n");
>>>>>>     			dmar_remove_one_dev_info(dev);
>>>>>>     			return ret;
>>>>>> --
>>>>>> 2.25.1
>>>>>
>>>>> It's cleaner to avoid this error at the first place, i.e. only do the
>>>>> setup when the first device is attached to the pasid table.
>>>>
>>>> The logic that identifies the first device might introduce additional
>>>> unnecessary complexity. Devices that share a pasid table are rare. I
>>>> even prefer to give up sharing tables so that the code can be
>>>> simpler.:-)
>>>>
>>>
>>> It's not that complex if you simply move device_attach_pasid_table()
>>> out of intel_pasid_alloc_table(). Then do the setup if
>>> list_empty(&pasid_table->dev) and then attach device to the
>>> pasid table in domain_add_dev_info().
>>
>> The pasid table is part of the device, hence a better place to
>> allocate/free the pasid table is in the device probe/release paths.
>> Things will become more complicated if we change relationship between
>> device and it's pasid table when attaching/detaching a domain. That's
>> the reason why I thought it was additional complexity.
>>
> 
> If you do want to follow current route it’s still cleaner to check
> whether the pasid entry has pointed to the domain in the individual
> setup function instead of blindly returning -EBUSY and then ignoring
> it even if a real busy condition occurs. The setup functions can
> just return zero for this benign alias case.

Fair enough. Let me improve it.

--
Best regards,
baolu