Re: [PATCH v1 1/8] iommu: Add iommu_group_replace_domain()

From: Lu Baolu <baolu.lu@linux.intel.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Stuart Yoder <stuyoder@gmail.com>,
	rafael@kernel.org, David Airlie <airlied@linux.ie>,
	linux-pci@vger.kernel.org,
	Thierry Reding <thierry.reding@gmail.com>,
	Diana Craciun <diana.craciun@oss.nxp.com>,
	Dmitry Osipenko <digetx@gmail.com>, Will Deacon <will@kernel.org>,
	Ashok Raj <ashok.raj@intel.com>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Christoph Hellwig <hch@infradead.org>,
	Kevin Tian <kevin.tian@intel.com>,
	Chaitanya Kulkarni <kch@nvidia.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	kvm@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Cornelia Huck <cohuck@redhat.com>,
	linux-kernel@vger.kernel.org, Li Yang <leoyang.li@nxp.com>,
	iommu@lists.linux-foundation.org,
	Jacob jun Pan <jacob.jun.pan@intel.com>,
	Daniel Vetter <daniel@ffwll.ch>,
	Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH v1 1/8] iommu: Add iommu_group_replace_domain()
Date: Fri, 7 Jan 2022 08:26:50 +0800	[thread overview]
Message-ID: <58e2d0d2-649a-a3f5-e8ae-9cbf2719015f@linux.intel.com> (raw)
In-Reply-To: <20220106170608.GI2328285@nvidia.com>

On 1/7/22 1:06 AM, Jason Gunthorpe wrote:
> On Thu, Jan 06, 2022 at 10:20:46AM +0800, Lu Baolu wrote:
>> Expose an interface to replace the domain of an iommu group for frameworks
>> like vfio which claims the ownership of the whole iommu group.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>>   include/linux/iommu.h | 10 ++++++++++
>>   drivers/iommu/iommu.c | 37 +++++++++++++++++++++++++++++++++++++
>>   2 files changed, 47 insertions(+)
>>
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index 408a6d2b3034..66ebce3d1e11 100644
>> +++ b/include/linux/iommu.h
>> @@ -677,6 +677,9 @@ void iommu_device_unuse_dma_api(struct device *dev);
>>   int iommu_group_set_dma_owner(struct iommu_group *group, void *owner);
>>   void iommu_group_release_dma_owner(struct iommu_group *group);
>>   bool iommu_group_dma_owner_claimed(struct iommu_group *group);
>> +int iommu_group_replace_domain(struct iommu_group *group,
>> +			       struct iommu_domain *old,
>> +			       struct iommu_domain *new);
>>   
>>   #else /* CONFIG_IOMMU_API */
>>   
>> @@ -1090,6 +1093,13 @@ static inline bool iommu_group_dma_owner_claimed(struct iommu_group *group)
>>   {
>>   	return false;
>>   }
>> +
>> +static inline int
>> +iommu_group_replace_domain(struct iommu_group *group, struct iommu_domain *old,
>> +			   struct iommu_domain *new)
>> +{
>> +	return -ENODEV;
>> +}
>>   #endif /* CONFIG_IOMMU_API */
>>   
>>   /**
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 72a95dea688e..ab8ab95969f5 100644
>> +++ b/drivers/iommu/iommu.c
>> @@ -3431,3 +3431,40 @@ bool iommu_group_dma_owner_claimed(struct iommu_group *group)
>>   	return user;
>>   }
>>   EXPORT_SYMBOL_GPL(iommu_group_dma_owner_claimed);
>> +
>> +/**
>> + * iommu_group_replace_domain() - Replace group's domain
>> + * @group: The group.
>> + * @old: The previous attached domain. NULL for none.
>> + * @new: The new domain about to be attached.
>> + *
>> + * This is to support backward compatibility for vfio which manages the dma
>> + * ownership in iommu_group level.
> 
> This should mention it can only be used with iommu_group_set_dma_owner()

Sure.

> 
>> +	if (old)
>> +		__iommu_detach_group(old, group);
>> +
>> +	if (new) {
>> +		ret = __iommu_attach_group(new, group);
>> +		if (ret && old)
>> +			__iommu_attach_group(old, group);
>> +	}
> 
> The sketchy error unwind here gives me some pause for sure. Maybe we
> should define that on error this leaves the domain as NULL
> 
> Complicates vfio a tiny bit to cope with this failure but seems
> cleaner than leaving it indeterminate.

Fair enough.

> 
> Jason
> 

Best regards,
baolu
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