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

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Date:   Mon, 6 Jul 2020 15:21:58 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     "Liu, Yi L" <yi.l.liu@...el.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 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


> 
>>> +		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.

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;
>>>  		}
>>>
>