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

[Baolu Lu]

On 2022/6/22 11:31, Tian, Kevin wrote:
> > 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.

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

Best regards,
baolu