RE: [PATCH v5 05/20] dma-pool: track decrypted atomic pools and select them via attrs

From: Jason Gunthorpe <jgg@ziepe.ca> Sent: Tuesday, June 2, 2026 5:55 PM

On Tue, Jun 02, 2026 at 02:24:40PM +0000, Michael Kelley wrote:

quoted

Except that in a normal VM, the "unencrypted" pool attribute does *not*
describe the state of the memory itself.  In a normal VM, the memory is
unencrypted, but the "unencrypted" pool attribute is false. That
contradiction is the essence of my concern.

I would argue no..

When CC is enabled the default state of memory in a Linux environment
is "encrypted". You have to take a special action to "decrypt" it.

Thus the default state of memory in a non-CC environment is also
paradoxically "encrypted" too. 

The need to have such an unnatural premise is usually an indication
of a conceptual problem with the overall model, or perhaps just a
terminology problem. 

Here's a proposal. The new DMA attribute is DMA_ATTR_CC_SHARED.
Name the pool attribute "cc_shared" instead of "unencrypted". Having
"cc_shared" set to false in a normal VM doesn't lead to the non-sensical
situation of claiming that a normal VM is encrypted. The boolean
"unencrypted" parameter that has been added to various calls also
becomes "cc_shared".  If "CC_SHARED" is a suitable name for the DMA
attribute, it ought to be suitable as the pool attribute. And everything
matches as well.

Michael  

"decryption" is impossible.

Therefore the "unencrypted" state is a special state that only memory
inside a CC VM can have. A normal VM can never have "unencrypted"
memory at all, so having it be false in the pool is accurate as far as
the APIs go.

un-encrypted = true means "the memory in this pool was transformed with
set_memory_decrypted()" - which is impossible on a normal VM.

Jason