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

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Liu, Yi L <yi.l.liu@intel.com>
> Sent: Saturday, June 27, 2020 2:53 PM
> 
> 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.
> 

yes, this likely requires a new uAPI thus it could come as an incremental patch
later. We may reuse the same structure as defined here for communicating
preferred values.

Thanks
Kevin
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