Re: [RFC PATCH v7 02/13] mm: Add an allocator for CoCo shared memory

On Wed, Sep 23, 2026 at 10:42:39AM +0100, Catalin Marinas wrote:

On pKVM, we want set_memory_decrypted() to zero the buffer
before the host can access it (I guess currently relying on __GFP_ZERO
allocations). Since no cryptographic encryption takes place, there's not
much point in memset'ing again after the operation as the content was
already zeroed.

It sounds like this a pkvm unique thing, since RMM always makes the
memory hidden, pkvm flow should do it too. Either inside its guest
set_memory_decrypted() or inside the hypervisor like RMM.

Hypervisor doing it is the right place, hypervisor always needs to
ensure guest memory is cleansed whenever the guest gives it up. Either
via a private to shared, unmap or just exiting.

I don't think cc_make_shared() has the right information on how to
safely and efficiently do the zeroing. That's only known to the
set_memory_* backend. So you'd have to propagate the flag down.

+1

Jason