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