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

[Tian, Kevin]

> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Wednesday, June 22, 2022 11:28 AM
> 
> On 2022/6/22 11:06, Tian, Kevin wrote:
> >> From: Baolu Lu<baolu.lu@xxxxxxxxxxxxxxx>
> >> Sent: Tuesday, June 21, 2022 5:04 PM
> >>
> >> 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;
> >> +}
> > 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.