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

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Message-ID: <DM5PR11MB143534C547D61ABAE5CCEDBFC3690@DM5PR11MB1435.namprd11.prod.outlook.com>
Date:   Mon, 6 Jul 2020 13:26:15 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Auger Eric <eric.auger@...hat.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "joro@...tes.org" <joro@...tes.org>
CC:     "Tian, Kevin" <kevin.tian@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>,
        "Sun, Yi Y" <yi.y.sun@...el.com>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "Wu, Hao" <hao.wu@...el.com>,
        "stefanha@...il.com" <stefanha@...il.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>
Subject: RE: [PATCH v4 03/15] iommu/smmu: Report empty domain nesting info

Hi Eric,

> From: Auger Eric <eric.auger@...hat.com>
> Sent: Monday, July 6, 2020 9:22 PM
> 
> Hi Yi,
> 
> On 7/6/20 2:46 PM, Liu, Yi L wrote:
> > Hi Eric,
> >
> >> From: Auger Eric <eric.auger@...hat.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@...nel.org>
> >>> Cc: Robin Murphy <robin.murphy@....com>
> >>> Cc: Eric Auger <eric.auger@...hat.com>
> >>> Cc: Jean-Philippe Brucker <jean-philippe@...aro.org>
> >>> Suggested-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
> >>> Signed-off-by: Liu Yi L <yi.l.liu@...el.com>
> >>> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.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?
> 
> I just suggested that by analogy with the VFIO argsz

I see. will change it.

> 
> >
> >>> +		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?
> 
> I understand this is a prerequisite. It was more as an information.
> Returning a void struct is a bit weird but at the moment I don't have anything better.

got you. do you think it is necessary to add your statement as a comment here?

Regards,
Yi Liu

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