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

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@nvidia.com>

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

alloc_pages_decrypted() ?

Jason