RE: [PATCH v5 03/15] iommu/smmu: Report empty domain nesting info

[Liu, Yi L]

Hi Will,

> From: Will Deacon <will@xxxxxxxxxx>
> Sent: Monday, July 13, 2020 9:15 PM
> 
> On Sun, Jul 12, 2020 at 04:20:58AM -0700, Liu Yi L wrote:
> > This patch is added as instead of returning a boolean for DOMAIN_ATTR_NESTING,
> > iommu_domain_get_attr() should return an iommu_nesting_info handle.
> >
> > Cc: Will Deacon <will@xxxxxxxxxx>
> > Cc: Robin Murphy <robin.murphy@xxxxxxx>
> > Cc: Eric Auger <eric.auger@xxxxxxxxxx>
> > Cc: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> > Suggested-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> > Signed-off-by: Liu Yi L <yi.l.liu@xxxxxxxxx>
> > Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > ---
> > v4 -> v5:
> > *) address comments from Eric Auger.
> > ---
> >  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..ec815d7 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;
> > +	unsigned int size;
> > +
> > +	if (!info || smmu_domain->stage != ARM_SMMU_DOMAIN_NESTED)
> > +		return -ENODEV;
> > +
> > +	size = sizeof(struct iommu_nesting_info);
> > +
> > +	/*
> > +	 * if provided buffer size is smaller than expected, 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;
> > +}
> 
> Have you verified that this doesn't break the existing usage of
> DOMAIN_ATTR_NESTING in drivers/vfio/vfio_iommu_type1.c?

I didn't have ARM machine on my hand. But I contacted with Jean
Philippe, he confirmed no compiling issue. I didn't see any code
getting DOMAIN_ATTR_NESTING attr in current drivers/vfio/vfio_iommu_type1.c.
What I'm adding is to call iommu_domai_get_attr(, DOMAIN_ATTR_NESTIN)
and won't fail if the iommu_domai_get_attr() returns 0. This patch
returns an empty nesting info for DOMAIN_ATTR_NESTIN and return
value is 0 if no error. So I guess it won't fail nesting for ARM.

@Eric, how about your opinion? your dual-stage vSMMU support may
also share the vfio_iommu_type1.c code.

Regards,
Yi Liu

> Will