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Tue, 27 Oct 2026 03:29:34 -0700 (PDT) Date: Tue, 27 Oct 2026 06:29:29 -0400 From: "Michael S. Tsirkin" To: Kevin Loughlin Cc: David Hildenbrand , Jason Wang , Eugenio =?iso-8859-1?Q?P=E9rez?= , Xuan Zhuo , Ard Biesheuvel , Kiryl Shutsemau , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Tom Lendacky , Ashish Kalra , Michael Roth , Rick Edgecombe , Andrew Morton , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Alexander Duyck , virtualization@lists.linux.dev, linux-coco@lists.linux.dev, linux-efi@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sidharth Telang , Punit Salian , Peter Gonda , Ackerley Tng , Jacky Li , Steve Rutherford , David Skidmore Subject: Re: [PATCH 00/13] virtio_balloon, efi/unaccepted: support memory ballooning and free page reporting in CoCo guests Message-ID: <20261027051245-mutt-send-email-mst@kernel.org> References: <20261027025616.1632690-1-kevinloughlin@google.com> X-Archived-By: MIME-Version: 1.0 In-Reply-To: <20261027025616.1632690-1-kevinloughlin@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: s8BbZxGY5OUF3IwZouJlBKgCFtjQFOoFiO0gZfwncuM_1793096976 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 0E59AC0005 X-Stat-Signature: w9ihcekrz411bdksmrreoh7r4if1tita X-Rspam-User: X-Spam-Status: No, score=-6.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1793096978-311314 X-HE-Meta: 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 GUhMfMml yO765P5opMBTuDfr/tN0JjObwkIvI8ArdFMrk1fu0jkyWeoXusRTx4yFXgB+e5OI+wG46wf9OcEEKmdrnx2UJovQOVyktXVvMSSgSH/lavUtMl5oal9a2BHUNObrJdOGpHNnjmZcQyuLqd7CXVHM5iYsEWfUFwnRu/o7eHbxviRNnaGUM2L4yVQawKtJZ9BhF61lYK6dFIoH52nEU57tqW7eM7k3w2MIzm8V8CQZUIbMdxPQ6NtnE4haBEs1GnrzRNIwOxI1YFsUi+4ogD55FeNyCr+G/XJ4/Llh2Ic5yCsjNOwR+Q9/ZBhi5a3ajGErgsAJW/M4rLcBxZY7nGPW+u726pO1DnqCcDSD+7R8cKYAiYFvjxxDPpdr/spgNt0cbQUEWhg5R3AoztllK/A8oH5mDxjEPlev0NO64HYcP9ag9U5A= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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