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

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

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;
+}
+
  /*
   * Set up the scalable mode pasid table entry for first only
   * translation type.
@@ -595,9 +605,8 @@ int intel_pasid_setup_first_level(struct intel_iommu 
*iommu,
  	if (WARN_ON(!pte))
  		return -EINVAL;

-	/* Caller must ensure PASID entry is not in use. */
  	if (pasid_pte_is_present(pte))
-		return -EBUSY;
+		return rid2pasid_domain_valid(pte, pasid, did) ? 0: -EBUSY;

  	pasid_clear_entry(pte);

@@ -698,9 +707,8 @@ int intel_pasid_setup_second_level(struct 
intel_iommu *iommu,
  		return -ENODEV;
  	}

-	/* Caller must ensure PASID entry is not in use. */
  	if (pasid_pte_is_present(pte))
-		return -EBUSY;
+		return rid2pasid_domain_valid(pte, pasid, did) ? 0: -EBUSY;

  	pasid_clear_entry(pte);
  	pasid_set_domain_id(pte, did);
@@ -738,9 +746,8 @@ int intel_pasid_setup_pass_through(struct 
intel_iommu *iommu,
  		return -ENODEV;
  	}

-	/* Caller must ensure PASID entry is not in use. */
  	if (pasid_pte_is_present(pte))
-		return -EBUSY;
+		return rid2pasid_domain_valid(pte, pasid, did) ? 0: -EBUSY;

  	pasid_clear_entry(pte);
  	pasid_set_domain_id(pte, did);

--
Best regards,
baolu