Re: [PATCH v9 01/14] mm: Add an allocator for CoCo shared memory

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 04/11/2026 16:45, Aneesh Kumar K.V (Arm) wrote:
> Confidential-computing guests may require memory shared with the host to
> be aligned and transitioned in units larger than PAGE_SIZE. Several DMA
> users need struct page-backed allocations satisfying these requirements.
> Provide a common allocator instead of requiring each user to open-code
> this sequence.
> 
> Add alloc_cc_shared_pages() and its node-aware variant. The allocator
> rounds the requested size to the architecture's shared granule,
> allocates suitably aligned contiguous pages and transitions the
> complete range to shared state. It also preserves the caller's GFP
> policy.
> 
> A private-to-shared transition may alter memory contents. Mask
> __GFP_ZERO from the underlying allocation and when requested, clear the
> complete transitioned range after cc_make_shared() succeeds.

This is not true for pKVM though. It is the other way around. i.e,
pages must be cleared before transition (e.g., from private to shared)
to make sure the contents don't leak into the host.

Do we need to handle such cases with a pre_conversion and 
post_conversion hook ?

Cheers
Suzuki