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

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2022/6/22 11:31, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@linux.intel.com>
>> Sent: Wednesday, June 22, 2022 11:28 AM
>>
>> On 2022/6/22 11:06, Tian, Kevin wrote:
>>>> From: Baolu Lu<baolu.lu@linux.intel.com>
>>>> Sent: Tuesday, June 21, 2022 5:04 PM
>>>>
>>>> On 2022/6/21 13:48, Tian, Kevin wrote:
>>>>>> From: Baolu Lu<baolu.lu@linux.intel.com>
>>>>>> Sent: Tuesday, June 21, 2022 12:28 PM
>>>>>>
>>>>>> On 2022/6/21 11:46, Tian, Kevin wrote:
>>>>>>>> From: Baolu Lu<baolu.lu@linux.intel.com>
>>>>>>>> Sent: Tuesday, June 21, 2022 11:39 AM
>>>>>>>>
>>>>>>>> On 2022/6/21 10:54, Tian, Kevin wrote:
>>>>>>>>>> From: Lu Baolu<baolu.lu@linux.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.
>>>> Kevin, how do you like this one?
>>>>
>>>> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
>>>> index cb4c1d0cf25c..ecffd0129b2b 100644
>>>> --- a/drivers/iommu/intel/pasid.c
>>>> +++ b/drivers/iommu/intel/pasid.c
>>>> @@ -575,6 +575,16 @@ static inline int pasid_enable_wpe(struct
>>>> pasid_entry *pte)
>>>>     	return 0;
>>>>     };
>>>>
>>>> +/*
>>>> + * Return true if @pasid is RID2PASID and the domain @did has already
>>>> + * been setup to the @pte. Otherwise, return false.
>>>> + */
>>>> +static inline bool
>>>> +rid2pasid_domain_valid(struct pasid_entry *pte, u32 pasid, u16 did)
>>>> +{
>>>> +	return pasid == PASID_RID2PASID && pasid_get_domain_id(pte) ==
>>>> did;
>>>> +}
>>> better this is not restricted to RID2PASID only, e.g.
>> pasid_pte_match_domain()
>>> and then read pasid from the pte to compare with the pasid argument.
>>>
>>
>> The pasid value is not encoded in the pasid table entry. This validity
>> check is only for RID2PASID as alias devices share the single RID2PASID
>> entry. For other cases, we should always return -EBUSY as what the code
>> is doing now.
>>
> 
> You are right.

Very appreciated for your input. I will update it with a v2.

Best regards,
baolu