RE: [PATCH v3 02/14] iommu: Report domain nesting info

["Liu, Yi L" <yi.l.liu@intel.com>]

Hi Robin,

> From: Robin Murphy <robin.murphy@arm.com>
> Sent: Saturday, June 27, 2020 12:05 AM
> 
> On 2020-06-26 08:47, Jean-Philippe Brucker wrote:
> > On Wed, Jun 24, 2020 at 01:55:15AM -0700, Liu Yi L wrote:
> >> IOMMUs that support nesting translation needs report the capability
> >> info to userspace, e.g. the format of first level/stage paging structures.
> >>
> >> This patch reports nesting info by DOMAIN_ATTR_NESTING. Caller can
> >> get nesting info after setting DOMAIN_ATTR_NESTING.
> >>
> >> v2 -> v3:
> >> *) remvoe cap/ecap_mask in iommu_nesting_info.
> >> *) reuse DOMAIN_ATTR_NESTING to get nesting info.
> >> *) return an empty iommu_nesting_info for SMMU drivers per Jean'
> >>     suggestion.
> >>
> >> Cc: Kevin Tian <kevin.tian@intel.com>
> >> CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
> >> Cc: Alex Williamson <alex.williamson@redhat.com>
> >> Cc: Eric Auger <eric.auger@redhat.com>
> >> Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> >> Cc: Joerg Roedel <joro@8bytes.org>
> >> Cc: Lu Baolu <baolu.lu@linux.intel.com>
> >> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> >> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> >> ---
> >>   drivers/iommu/arm-smmu-v3.c | 29 ++++++++++++++++++++--
> >>   drivers/iommu/arm-smmu.c    | 29 ++++++++++++++++++++--
> >
> > Looks reasonable to me. Please move the SMMU changes to a separate
> > patch and Cc the SMMU maintainers:
> 
> Cheers Jean, I'll admit I've been skipping over a lot of these patches lately :)
> 
> A couple of comments below...
> 
> >
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Robin Murphy <robin.murphy@arm.com>
> >
> > Thanks,
> > Jean
> >
> >>   include/uapi/linux/iommu.h  | 59
> +++++++++++++++++++++++++++++++++++++++++++++
> >>   3 files changed, 113 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/iommu/arm-smmu-v3.c
> >> b/drivers/iommu/arm-smmu-v3.c index f578677..0c45d4d 100644
> >> --- a/drivers/iommu/arm-smmu-v3.c
> >> +++ b/drivers/iommu/arm-smmu-v3.c
> >> @@ -3019,6 +3019,32 @@ static struct iommu_group
> *arm_smmu_device_group(struct device *dev)
> >>   	return group;
> >>   }
> >>
> >> +static int arm_smmu_domain_nesting_info(struct arm_smmu_domain
> *smmu_domain,
> >> +					void *data)
> >> +{
> >> +	struct iommu_nesting_info *info = (struct iommu_nesting_info *) data;
> >> +	u32 size;
> >> +
> >> +	if (!info || smmu_domain->stage != ARM_SMMU_DOMAIN_NESTED)
> >> +		return -ENODEV;
> >> +
> >> +	size = sizeof(struct iommu_nesting_info);
> >> +
> >> +	/*
> >> +	 * if provided buffer size is not equal to the size, should
> >> +	 * return 0 and also the expected buffer size to caller.
> >> +	 */
> >> +	if (info->size != size) {
> >> +		info->size = size;
> >> +		return 0;
> >> +	}
> >> +
> >> +	/* report an empty iommu_nesting_info for now */
> >> +	memset(info, 0x0, size);
> >> +	info->size = size;
> >> +	return 0;
> >> +}
> >> +
> >>   static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
> >>   				    enum iommu_attr attr, void *data)
> >>   {
> >> @@ -3028,8 +3054,7 @@ static int arm_smmu_domain_get_attr(struct
> iommu_domain *domain,
> >>   	case IOMMU_DOMAIN_UNMANAGED:
> >>   		switch (attr) {
> >>   		case DOMAIN_ATTR_NESTING:
> >> -			*(int *)data = (smmu_domain->stage ==
> ARM_SMMU_DOMAIN_NESTED);
> >> -			return 0;
> >> +			return arm_smmu_domain_nesting_info(smmu_domain,
> data);
> >>   		default:
> >>   			return -ENODEV;
> >>   		}
> >> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> >> index 243bc4c..908607d 100644
> >> --- a/drivers/iommu/arm-smmu.c
> >> +++ b/drivers/iommu/arm-smmu.c
> >> @@ -1506,6 +1506,32 @@ static struct iommu_group
> *arm_smmu_device_group(struct device *dev)
> >>   	return group;
> >>   }
> >>
> >> +static int arm_smmu_domain_nesting_info(struct arm_smmu_domain
> *smmu_domain,
> >> +					void *data)
> >> +{
> >> +	struct iommu_nesting_info *info = (struct iommu_nesting_info *) data;
> >> +	u32 size;
> >> +
> >> +	if (!info || smmu_domain->stage != ARM_SMMU_DOMAIN_NESTED)
> >> +		return -ENODEV;
> >> +
> >> +	size = sizeof(struct iommu_nesting_info);
> >> +
> >> +	/*
> >> +	 * if provided buffer size is not equal to the size, should
> >> +	 * return 0 and also the expected buffer size to caller.
> >> +	 */
> >> +	if (info->size != size) {
> >> +		info->size = size;
> >> +		return 0;
> >> +	}
> >> +
> >> +	/* report an empty iommu_nesting_info for now */
> >> +	memset(info, 0x0, size);
> >> +	info->size = size;
> >> +	return 0;
> >> +}
> >> +
> >>   static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
> >>   				    enum iommu_attr attr, void *data)
> >>   {
> >> @@ -1515,8 +1541,7 @@ static int arm_smmu_domain_get_attr(struct
> iommu_domain *domain,
> >>   	case IOMMU_DOMAIN_UNMANAGED:
> >>   		switch (attr) {
> >>   		case DOMAIN_ATTR_NESTING:
> >> -			*(int *)data = (smmu_domain->stage ==
> ARM_SMMU_DOMAIN_NESTED);
> >> -			return 0;
> >> +			return arm_smmu_domain_nesting_info(smmu_domain,
> data);
> >>   		default:
> >>   			return -ENODEV;
> >>   		}
> >> diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
> >> index 1afc661..898c99a 100644
> >> --- a/include/uapi/linux/iommu.h
> >> +++ b/include/uapi/linux/iommu.h
> >> @@ -332,4 +332,63 @@ struct iommu_gpasid_bind_data {
> >>   	} vendor;
> >>   };
> >>
> >> +/*
> >> + * struct iommu_nesting_info - Information for nesting-capable IOMMU.
> >> + *				user space should check it before using
> >> + *				nesting capability.
> >> + *
> >> + * @size:	size of the whole structure
> >> + * @format:	PASID table entry format, the same definition with
> >> + *		@format of struct iommu_gpasid_bind_data.
> >> + * @features:	supported nesting features.
> >> + * @flags:	currently reserved for future extension.
> >> + * @data:	vendor specific cap info.
> >> + *
> >> + * +---------------+----------------------------------------------------+
> >> + * | feature       |  Notes                                             |
> >> + *
> >>
> ++===============+============================================
> =======
> >> +=+
> >> + * | SYSWIDE_PASID |  Kernel manages PASID in system wide, PASIDs used  |
> >> + * |               |  in the system should be allocated by host kernel  |
> >> + * +---------------+----------------------------------------------------+
> >> + * | BIND_PGTBL    |  bind page tables to host PASID, the PASID could   |
> >> + * |               |  either be a host PASID passed in bind request or  |
> >> + * |               |  default PASIDs (e.g. default PASID of aux-domain) |
> >> + * +---------------+----------------------------------------------------+
> >> + * | CACHE_INVLD   |  mandatory feature for nesting capable IOMMU       |
> >> + *
> >> ++---------------+---------------------------------------------------
> >> +-+
> >> + *
> >> + */
> >> +struct iommu_nesting_info {
> >> +	__u32	size;
> >> +	__u32	format;
> >> +	__u32	features;
> >> +#define IOMMU_NESTING_FEAT_SYSWIDE_PASID	(1 << 0)
> >> +#define IOMMU_NESTING_FEAT_BIND_PGTBL		(1 << 1)
> >> +#define IOMMU_NESTING_FEAT_CACHE_INVLD		(1 << 2)
> >> +	__u32	flags;
> >> +	__u8	data[];
> >> +};
> >> +
> >> +/*
> >> + * struct iommu_nesting_info_vtd - Intel VT-d specific nesting info
> >> + *
> >> + *
> >> + * @flags:	VT-d specific flags. Currently reserved for future
> >> + *		extension.
> >> + * @addr_width:	The output addr width of first level/stage translation
> >> + * @pasid_bits:	Maximum supported PASID bits, 0 represents no PASID
> >> + *		support.
> >> + * @cap_reg:	Describe basic capabilities as defined in VT-d capability
> >> + *		register.
> >> + * @ecap_reg:	Describe the extended capabilities as defined in VT-d
> >> + *		extended capability register.
> >> + */
> >> +struct iommu_nesting_info_vtd {
> >> +	__u32	flags;
> >> +	__u16	addr_width;
> 
> I think this might be worth promoting to a generic feature - Arm has the same
> notion of intermediate address size, and I'd imagine that pretty much any other
> two-stage translation system would as well (either explicitly or implicitly).
> It also
> comes close to something the DPDK folks raised where they wanted parity with a
> feature that currently scrapes AGAW out of some VT-d-specific place, so
> abstracting it to completely generic code, in a way that could eventually be
> generalised to reporting info for non-nested domains too, would be really nice.

got you. I can do that.

> What would also be cool is if the user was able to pass in a structure with
> preferred values for the address size and other capabilities when they request
> nesting in the first place. Right now we'll always set up the maximum possible
> sized page table for any domain, but if we knew ahead of time how many bits the
> user actually cared about then we could potentially be more efficient (e.g. use
> fewer levels of pagetable or a different translation granule).

agreed, and I guess only the configurable caps (like the addr_width, domain
could have different addr_width per user request). I think it may be an
optimization afterward. Here, we report all the nesting related caps to user,
thus user could either do pre-check or expose correct capability to guest per
hardware support. This is necesary as nesting requires guest to maintain page
tables per hw supporting.

Regards,
Yi Liu

> Robin.
> 
> >> +	__u16	pasid_bits;
> >> +	__u64	cap_reg;
> >> +	__u64	ecap_reg;
> >> +};
> >> +
> >>   #endif /* _UAPI_IOMMU_H */
> >> --
> >> 2.7.4
> >>