RE: [PATCH v4 03/15] iommu/smmu: Report empty domain nesting info

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

Hi Eric,

> From: Auger Eric <eric.auger@redhat.com>
> 
> Hi Yi,
> 
> Please add a commit message: instead of returning a boolean for
> DOMAIN_ATTR_NESTING, arm_smmu_domain_get_attr() returns a
> iommu_nesting_info handle.

will do. thanks for the suggestion.

> 
> On 7/4/20 1:26 PM, Liu Yi L wrote:
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Robin Murphy <robin.murphy@arm.com>
> > Cc: Eric Auger <eric.auger@redhat.com>
> > Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > Suggested-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > 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 +++++++++++++++++++++++++++--
> >  2 files changed, 54 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) {
> < size?

< size may work as well. but I'd like the caller provide exact buffer size. not sure
if it is demand in kernel. do you have any suggestion?

> > +		info->size = size;
> > +		return 0;
> > +	}
> > +
> > +	/* report an empty iommu_nesting_info for now */
> > +	memset(info, 0x0, size);
> > +	info->size = size;
> For info, the current SMMU NESTED mode is not enabling any nesting. It just forces
> the usage of the 2st stage instead of stage1 for single stage translation.

yep. The intention is as below:

" However it requires changing the get_attr(NESTING) implementations in both
SMMU drivers as a precursor of this series, to avoid breaking
VFIO_TYPE1_NESTING_IOMMU on Arm. Since we haven't yet defined the
nesting_info structs for SMMUv2 and v3, I suppose we could return an empty
struct iommu_nesting_info for now?"
https://lore.kernel.org/linux-iommu/20200617143909.GA886590@myrica/

do you think any other needs to be done for now?

Regards,
Yi Liu

> Thanks
> 
> Eric
> > +	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;
> >  		}
> >