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[109.81.29.251]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42cb7f2e598sm32381240f8f.4.2025.11.25.00.45.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Nov 2025 00:45:39 -0800 (PST) Date: Tue, 25 Nov 2025 09:45:38 +0100 From: Michal Hocko To: Joshua Hahn Cc: Andrew Morton , Vlastimil Babka , Mike Rapoport , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com Subject: Re: [PATCH v2 2/2] mm/mm_init: decouple page checking and init_on_{alloc, free} Message-ID: References: <20251124225408.2243564-1-joshua.hahnjy@gmail.com> <20251124225408.2243564-2-joshua.hahnjy@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251124225408.2243564-2-joshua.hahnjy@gmail.com> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 06B98C0005 X-Stat-Signature: 6eda1o6pf8rwurfmy4c64disubctwy5x X-Rspam-User: X-HE-Tag: 1764060341-163915 X-HE-Meta: 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 3LnHj0b1 rkLduD54r6xRM/sM3Va3LiV81e4pD6VFM3nD8lACXWQyTxnTxOXURtepmYCn6qMJsBFVcZgRCWivcR26Hy94o2Pe5RkMBbI0QDMb7j5uqSfPGW+jZ12skIFyiiUzKibUfSFiI89iUxFW0QDP5bSq6Cgg+2RlnkP/4ALgCmpSQ4w3uds6VtVfQ9AWu9rbvVgkbPmYK+25nIRl68c0pHaQfkpmQoNNLdR3JHO8s1L8Bz4u8YA6JNimNE2aJfnFFIPHwLvOLlW3BGg70pLRGgQ7gH4UG/i0IqIWkDGmfyyz86YO19uBE9SuyeOpmHx12hlIz3ZKFGntzXne9fIrSyr5bfC9CblYi5bCxjNyesnAP0leUbpEi7WIBvXab+et7uzEzslviivWQkXfMpqyyokwxuqLY+jBvtQZBYPq0/4pc8j0H7q+mnw9oNKhtpuOam3Adqq8QZkYHOn6gZTwvMOC6rS9tM79b9S9vowvs X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon 24-11-25 14:54:07, Joshua Hahn wrote: > init_on_alloc and init_on_free protect the kernel by initializing > allocated and freed pages to 0 on allocation time / deletion. > Commit 700d2e9a36b93601270c1e15550acde2521386c5 ("mm, page_alloc: reduce > page alloc/free sanity checks") removed page checking from hot pcp > drain and refill paths, and instead coupled it with CONFIG_DEBUG_VM, > debug_pagealloc, page poisoning, and init_on_{alloc, free}. > > As the commit suggests, the first three turn the kernel into a debug > kernel, while the last hardens the kernel against leaking sensitive memory. > While enabling page checking is relatively low-cost and tying it > together with page initialization is not unreasonable, it does feel like > a bit of a side-effect, rather than an obvious consequence. > > With page checking now pulled out as a boot time parameter that can be > set independently, let's decouple page checking and init_on_alloc and > init_on_free. > > As a direct side effect, systems that have init_on_alloc or init_on_free > will no longer have page checking enabled by default; they will either > have to pass the check_pages boot parameter, build the kernel with > CONFIG_DEBUG_VM, or enable debug_pagealloc / page poisoning. How come this will not break existing users? What is an actual upside to get for the risk involved? -- Michal Hocko SUSE Labs