Re: [PATCH 00/13] virtio_balloon, efi/unaccepted: support memory ballooning and free page reporting in CoCo guests

[Michael S. Tsirkin]

On Tue, Oct 27, 2026 at 02:56:03AM +0000, Kevin Loughlin wrote:
> This series enables virtio-balloon free page reporting and memory balloon
> inflation/deflation in Confidential Computing (CoCo) guests, starting
> with architectural hooks implemented for AMD SEV variants, in order to
> support dynamic CoCo guest resizing.
> 
> Today, memory ballooning and free page reporting are essentially unusable
> in CoCo guests due to three main roadblocks:


For me, the bigger question is not whether we can, but whether we
should. Considerations I would like to see addressed:

Security, e.g.: does knowing which memory is free leak information from
the guest? If no, why not?
Consider CONFIG_SHUFFLE_PAGE_ALLOCATOR, RANDSTRUCT, etc.

correctness, e.g.:  Linux has init on free (and default on windows), if
initialized pages are dropped and host can not be trusted, they have to be
re-initialized. Is this handled? I don't see it in code.

Also, performance, e.g.: How much does this re-initialization cost?

Management: it was simple with balloon off unconditionally.
Now we are in murkier waters with various features offering
various performance/security tradeoffs.
What if some guests want the tradeoffs but others don't?

Documentation: for all of the above.

-- 
MST