linux-kernel - Re: [PATCH v3 3/7] dma-buf: Document RDMA non-ODP invalidate

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Message-ID: <8a8ba092-6cfa-41d2-8137-e5e9d917e914@amd.com>
Date: Wed, 21 Jan 2026 14:52:53 +0100
From: Christian König <christian.koenig@....com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Leon Romanovsky <leon@...nel.org>, Sumit Semwal
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Subject: Re: [PATCH v3 3/7] dma-buf: Document RDMA non-ODP
 invalidate_mapping() special case

On 1/21/26 14:18, Jason Gunthorpe wrote:
> On Wed, Jan 21, 2026 at 10:17:16AM +0100, Christian König wrote:
>> The whole idea is to make invalidate_mappings truly optional.
> 
> But it's not really optional! It's absence means we are ignoring UAF
> security issues when the exporters do their move_notify() and nothing
> happens.

No that is unproblematic.

See the invalidate_mappings callback just tells the importer that the mapping in question can't be relied on any more.

But the mapping is truly freed only by the importer calling dma_buf_unmap_attachment().

In other words the invalidate_mappings give the signal to the importer to disable all operations and the dma_buf_unmap_attachment() is the signal from the importer that the housekeeping structures can be freed and the underlying address space or backing object re-used.

Regards,
Christian.

> 
> Given this I don't want to loose the warning log either, the situation
> needs to be reported..
> 
> Jason