Re: [PATCH v8 02/11] iommu: Add max_pasids field in struct dev_iommu

[Baolu Lu]

On 2022/6/10 03:01, Raj, Ashok wrote:
> On Tue, Jun 07, 2022 at 09:49:33AM +0800, Lu Baolu wrote:
> > Use this field to save the number of PASIDs that a device is able to
> > consume. It is a generic attribute of a device and lifting it into the
> > per-device dev_iommu struct could help to avoid the boilerplate code
> > in various IOMMU drivers.
> >
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >   include/linux/iommu.h |  2 ++
> >   drivers/iommu/iommu.c | 26 ++++++++++++++++++++++++++
> >   2 files changed, 28 insertions(+)
> >
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index 03fbb1b71536..d50afb2c9a09 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -364,6 +364,7 @@ struct iommu_fault_param {
> >    * @fwspec:	 IOMMU fwspec data
> >    * @iommu_dev:	 IOMMU device this device is linked to
> >    * @priv:	 IOMMU Driver private data
> > + * @max_pasids:  number of PASIDs device can consume
> >    *
> >    * TODO: migrate other per device data pointers under iommu_dev_data, e.g.
> >    *	struct iommu_group	*iommu_group;
> > @@ -375,6 +376,7 @@ struct dev_iommu {
> >   	struct iommu_fwspec		*fwspec;
> >   	struct iommu_device		*iommu_dev;
> >   	void				*priv;
> > +	u32				max_pasids;
> >   };
> >   
> >   int iommu_device_register(struct iommu_device *iommu,
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index 847ad47a2dfd..adac85ccde73 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -20,6 +20,7 @@
> >   #include <linux/idr.h>
> >   #include <linux/err.h>
> >   #include <linux/pci.h>
> > +#include <linux/pci-ats.h>
>
> Is this needed for this patch?

Yes. It's for pci_max_pasids().

> >   #include <linux/bitops.h>
> >   #include <linux/property.h>
> >   #include <linux/fsl/mc.h>
> > @@ -218,6 +219,30 @@ static void dev_iommu_free(struct device *dev)
> >   	kfree(param);
> >   }
> >   
> > +static u32 dev_iommu_get_max_pasids(struct device *dev)
> > +{
> > +	u32 max_pasids = dev->iommu->iommu_dev->max_pasids;
> > +	u32 num_bits;
> > +	int ret;
> > +
> > +	if (!max_pasids)
> > +		return 0;
> > +
> > +	if (dev_is_pci(dev)) {
> > +		ret = pci_max_pasids(to_pci_dev(dev));
> > +		if (ret < 0)
> > +			return 0;
> > +
> > +		return min_t(u32, max_pasids, ret);
>
> Ah.. that answers my other question to consider device pasid-max. I guess
> if we need any enforcement of restricting devices that aren't supporting
> the full PASID, that will be done by some higher layer?

The mm->pasid style of SVA is explicitly enabled through
iommu_dev_enable_feature(IOMMU_DEV_FEAT_SVA). The IOMMU driver specific
restriction might be put there?

> too many returns in this function, maybe setup all returns to the end of
> the function might be elegant?

I didn't find cleanup room after a quick scan of the code. But sure, let
me go through code again offline.

> > +	}
> > +
> > +	ret = device_property_read_u32(dev, "pasid-num-bits", &num_bits);
> > +	if (ret)
> > +		return 0;
> > +
> > +	return min_t(u32, max_pasids, 1UL << num_bits);
> > +}
> > +
> >   static int __iommu_probe_device(struct device *dev, struct list_head *group_list)
> >   {
> >   	const struct iommu_ops *ops = dev->bus->iommu_ops;
> > @@ -243,6 +268,7 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list
> >   	}
> >   
> >   	dev->iommu->iommu_dev = iommu_dev;
> > +	dev->iommu->max_pasids = dev_iommu_get_max_pasids(dev);
> >   
> >   	group = iommu_group_get_for_dev(dev);
> >   	if (IS_ERR(group)) {
> > --
> > 2.25.1

Best regards,
Baolu