Re: [PATCH RFC 01/11] iommu: Add pasid_bits field in struct dev_iommu

[Lu Baolu]

On 2022/3/21 15:01, Tian, Kevin wrote:
> > From: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Sunday, March 20, 2022 2:40 PM
> >
> > Use this field to save the pasid/ssid bits that a device is able to
> > support with its IOMMU hardware. It is a generic attribute of a device
> > and lifting it into the per-device dev_iommu struct makes it possible
> > to allocate a PASID for device without calls into the IOMMU drivers.
> > Any iommu driver which suports PASID related features should set this
> > field before features are enabled on the devices.
> >
> > Signed-off-by: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >   include/linux/iommu.h                       | 1 +
> >   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 1 +
> >   drivers/iommu/intel/iommu.c                 | 5 ++++-
> >   3 files changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index 6ef2df258673..36f43af0af53 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -368,6 +368,7 @@ struct dev_iommu {
> >   	struct iommu_fwspec		*fwspec;
> >   	struct iommu_device		*iommu_dev;
> >   	void				*priv;
> > +	unsigned int			pasid_bits;
> >   };
> >
> >   int iommu_device_register(struct iommu_device *iommu,
> > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > index 627a3ed5ee8f..8e262210b5ad 100644
> > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > @@ -2812,6 +2812,7 @@ static int arm_smmu_dev_enable_feature(struct
> > device *dev,
> >   		master->iopf_enabled = true;
> >   		return 0;
> >   	case IOMMU_DEV_FEAT_SVA:
> > +		dev->iommu->pasid_bits = master->ssid_bits;
> >   		return arm_smmu_master_enable_sva(master);
> >   	default:
> >   		return -EINVAL;
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index 6f7485c44a4b..c1b91bce1530 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -4587,8 +4587,11 @@ static struct iommu_device
> > *intel_iommu_probe_device(struct device *dev)
> >   			if (pasid_supported(iommu)) {
> >   				int features = pci_pasid_features(pdev);
> >
> > -				if (features >= 0)
> > +				if (features >= 0) {
> >   					info->pasid_supported = features | 1;
> > +					dev->iommu->pasid_bits =
> > +						fls(pci_max_pasids(pdev)) - 1;
> Original intel_svm_alloc_pasid() covers both PCI and non-PCI devices:
>
> 	ioasid_t max_pasid = dev_is_pci(dev) ?
> 		pci_max_pasids(to_pci_dev(dev)) : intel_pasid_max_id;
>
> though I'm not sure whether non-PCI SVA has been supported indeed, this
> patch implies a functional change here.

The info->pasid_supported is only set for PCI devices. So the status is
that non-PCI SVA hasn't been supported. No functional change here from
this point of view.

Best regards,
baolu