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

[Tian, Kevin]

> 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.

> +
>   /*
>    * 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