RE: [PATCH v3 15/15] iommufd: Add a selftest

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> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Friday, November 4, 2022 9:01 AM
> 
> The only way I can see to solve this is to hold a serializing lock
> across iommufd_access_pin_pages() so that neither
> iommufd_test_access_unmap() can progress until both the pin is
> completed and the record of the pin is stored.

same as gvt does which maintains an internal mapping cache and
conducts pin/unmap with cache update under the mutex protection.

> 
> Fortunately in the iommufd design we can hold a lock like this across
> these calls, and in the op callback, without deadlocking. I can't
> recall if vfio can do the same, I suspect not since I had in my mind I
> needed to avoid that kind of locking for deadlock reasons..

I think so. iiuc vfio relies on driver to ensure serialization in this scenario.




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