Re: [PATCH 0/2] Clear shared pages after private-to-shared conversion

[Jason Gunthorpe]

On Thu, Aug 20, 2026 at 11:50:23AM +0100, Steven Price wrote:
> Arm CCA includes "Memory Encryption Contexts" (MEC) which allows the
> private and shared data accessible to a guest to have different memory
> encryption keys. Consequently when converting memory to shared, the
> memory encryption key used to access the physical page will change.
> 
> Both the GICv3 ITS driver and the system_cc_shared dma-buf heap
> currently allocate memory with __GFP_ZERO and then decrypt it. With MEC
> the zeroing is done with the wrong encryption key and the data visible
> after decryption may be ciphertext. The RMM is required to scrub the
> data, but may perform this scrub with a different encryption key to the
> eventual key that will be used for shared access.
> 
> Fix these two sites by avoiding the __GFP_ZERO during the allocation and
> performing a clear_pages() call after the decryption.

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

This whole set_memory_decrypted() API is awful. It really should be improved.

alloc_pages_decrypted() ?

Jason