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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: <20261027163814-mutt-send-email-mst@kernel.org> References: <20261027025616.1632690-1-kevinloughlin@google.com> <20261027051245-mutt-send-email-mst@kernel.org> X-Archived-By: MIME-Version: 1.0 In-Reply-To: <20261027051245-mutt-send-email-mst@kernel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: PeyRmUMGSLH9LT_U2-tCmMmVhrm5UL7aZCVv4mD_Bno_1793133569 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: F25F880003 X-Stat-Signature: 5nzdt46yzno9fhqtwnwy4afz3xmpaqqh X-Rspam-User: X-Spam-Status: No, score=-11.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793133571-358739 X-HE-Meta: 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 oy3vFdSu 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 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 06:29:35AM -0400, Michael S. Tsirkin wrote: > 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 And to give this a bit more perspective, I present: commit ab676b7d6fbf4b294bf198fb27ade5b0e865c7ce Author: Kiryl Shutsemau Date: Mon Mar 9 23:11:12 2015 +0200 pagemap: do not leak physical addresses to non-privileged userspace As pointed by recent post[1] on exploiting DRAM physical imperfection, /proc/PID/pagemap exposes sensitive information which can be used to do attacks. This disallows anybody without CAP_SYS_ADMIN to read the pagemap. [1] http://googleprojectzero.blogspot.com/2015/03/exploiting-dram-rowhammer-bug-to-gain.html [ Eventually we might want to do anything more finegrained, but for now this is the simple model. - Linus ] Signed-off-by: Kirill A. Shutemov Acked-by: Konstantin Khlebnikov Acked-by: Andy Lutomirski Cc: Pavel Emelyanov Cc: Andrew Morton Cc: Mark Seaborn Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds Leaking phys addresses to unpriveleged entities might not be wise. -- MST