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Wed, 11 Nov 2026 00:16:47 -0800 (PST) Received: from localhost ([199.201.64.8]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b181fc804csm1360430a91.1.2026.11.11.00.16.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Nov 2026 00:16:47 -0800 (PST) Date: Wed, 11 Nov 2026 00:16:43 -0800 From: Chris Down To: Mike Rapoport Cc: pasha.tatashin@soleen.com, pratyush@kernel.org, graf@amazon.com, kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH] kho: Prevent reuse of preserved pages after a reservation failure Message-ID: References: X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.3.3 (9073d26d) (2026-06-12) X-Stat-Signature: qupdj1emcds51emwtrh4reobdcjpdorz X-Rspamd-Queue-Id: 070AA40004 X-Rspam-User: X-Rspamd-Server: rspam08 X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1794385008-598003 X-HE-Meta: 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 ahHJEjPq IL56rzZRm95iJ+xs/32VTR0RFgiZL5YFzoMlfySJIejKrJbwTacpAb3nkgkRPlePLTg4XCbiaXP/g41GXypZBBYjmDONtVBIsDZIVzayFC3ZE34lcyEWErClbMKoPhox5YsMWSqn1fRoTKhJTQxpmkxv7Hf3etwA4cL8b6eT2LQBBbXIhE3cKAa4cEsEvTrkKD62Vi93O/IsKUXLa00CvHMfukz0QKOKoP3UYy1dauSE9LTANVd72dbcrjft0csJAhC9qV27+bnf1sc/JMbzKtYLq7txO4ekNSXl++U4Ny0scY88lValyRtqEoh3Zqvsjrn4XkrhgkQfnH6UlBgLzEhkYL/z0B36GfoHv5IMzjCh6Gm5v313gqCKP4u9De0sDBlmuF4zjtugJQGSKgo5qUAb9XT83y3/PviMJgPsyPb5nguNs/BdLazsqSYwsKf8QbRhiWeHj5F0CPkp7GdC9lgQRrA== 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 Hi Mike, Mike Rapoport writes: >On Tue, Nov 10, 2026 at 11:09:30PM -0800, Chris Down wrote: >> kho_preserved_memory_reserve() reserves each range of preserved memory >> in memblock and marks it noinit, but ignores both return values. Either >> can fail when memblock has to grow its reserved array and can't find >> room, which at this point in boot it may only take from KHO bootmem. > >Is it an LLM analysis or you seen this happen? Are those the only two options nowadays! :-) In this case it's just eyeballs. I happened to notice this while preparing my KHO/LUO observability patchset and thought it made sense to send as a separate patch, since it doesn't depend on anything there. It's probably realistically quite unlikely, I would think it would require a lot of fragmentation or a very small kho_bootmem=. >> Dropping the handover at this point isn't safe either. reserve_mem= >> revives its regions from the handover before mm_core_init(), and >> relies on this walk to reserve them. > >reserve_mem_kho_revive() can memblock_reserve() its memory itself and we >can carry on, can't we? Thanks, that's better. I had thought carryong on wasn't possible because reserve_mem has already reserved its regions by the time we get to the walk, but actually you're right that there's no reason reserve_mem_kho_revive() can't just do it itself... Looking at the code one thing we would likely trip over then is that kho_mem_retrieve()'s error path only clears fdt_phys, but not bootmem_phys. kho_init() then thinks that it's a cold boot and runs init_cma_reserved_pageblock() over the inherited bootmem which has already been handed to the buddy allocator, so this would need adjustment first. So then, let me send v2 with reserve_mem_kho_revive() sorting out its own range, and making kho_init() skip the bootmem setup when the bootmem was inherited, if that sounds good? Thanks! Chris