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From:   "Liu, Yi L" <yi.l.liu@intel.com>
To:     Will Deacon <will@kernel.org>
CC:     "alex.williamson@redhat.com" <alex.williamson@redhat.com>,
        "eric.auger@redhat.com" <eric.auger@redhat.com>,
        "baolu.lu@linux.intel.com" <baolu.lu@linux.intel.com>,
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        "Tian, Kevin" <kevin.tian@intel.com>,
        "jacob.jun.pan@linux.intel.com" <jacob.jun.pan@linux.intel.com>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "Tian, Jun J" <jun.j.tian@intel.com>,
        "Sun, Yi Y" <yi.y.sun@intel.com>,
        "jean-philippe@linaro.org" <jean-philippe@linaro.org>,
        "peterx@redhat.com" <peterx@redhat.com>,
        "Wu, Hao" <hao.wu@intel.com>,
        "stefanha@gmail.com" <stefanha@gmail.com>,
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        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Robin Murphy <robin.murphy@arm.com>
Subject: RE: [PATCH v5 03/15] iommu/smmu: Report empty domain nesting info
Thread-Topic: [PATCH v5 03/15] iommu/smmu: Report empty domain nesting info
Thread-Index: AQHWWD2lVc+q/avNRU2WMQZyTvsTFakFfrYAgAFdguA=
Date:   Tue, 14 Jul 2020 10:12:49 +0000
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Hi Will,

> From: Will Deacon <will@kernel.org>
> Sent: Monday, July 13, 2020 9:15 PM
>=20
> 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_N=
ESTING,
> > iommu_domain_get_attr() should return an iommu_nesting_info handle.
> >
> > 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>
> > ---
> > 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 =3D (struct iommu_nesting_info *)data=
;
> > +	unsigned int size;
> > +
> > +	if (!info || smmu_domain->stage !=3D ARM_SMMU_DOMAIN_NESTED)
> > +		return -ENODEV;
> > +
> > +	size =3D 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 =3D size;
> > +		return 0;
> > +	}
> > +
> > +	/* report an empty iommu_nesting_info for now */
> > +	memset(info, 0x0, size);
> > +	info->size =3D size;
> > +	return 0;
> > +}
>=20
> 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