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

[Baolu Lu]

On 2022/6/21 13:48, Tian, Kevin wrote:
> > From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Tuesday, June 21, 2022 12:28 PM
> >
> > On 2022/6/21 11:46, Tian, Kevin wrote:
> > > > From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> > > > Sent: Tuesday, June 21, 2022 11:39 AM
> > > >
> > > > On 2022/6/21 10:54, Tian, Kevin wrote:
> > > > > > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > > > > > 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