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b=AEut25SD+vng87R7XeaR2L7VNOmfVGVWR8pCR4lj6hxHh+55pTmQmBMT709BMzQLW CB/33no3pprN6vVOd2QzKCvVyeULRCz3POv7imFfjNXyGnZTpLULF7gmChlyxwBifx pBM03+YdvpYUyEb5DO+ZToSnYQnEoNcMiWFJC3HIx7Lt9yCKjPR8KvwMpxj8mVU4L5 Ltm+Q3RxvDJeHTPxK3sM8R/KE/U0juXpWlQchg5c9iqzn1pEyIyhtDISzxaM6ecoar 6N4e9v5BZe1yCJ2dlVWTg8rTnzyUCPkRtIwv1+4NfrhW73SqcchrVEgB77yJ5EWk8k zEwKllGgjkRyg== From: SeongJae Park To: Joshua Hahn Cc: SeongJae Park , 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} Date: Mon, 24 Nov 2025 17:18:07 -0800 Message-ID: <20251125011808.74845-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251124225408.2243564-2-joshua.hahnjy@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0D2E7100004 X-Stat-Signature: y9ckpipg7y6chxt8sk79dikib71ski8n X-Rspam-User: X-HE-Tag: 1764033496-631873 X-HE-Meta: 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 mdlN687u YpVKgU+EGOjwbsRiWLaMdAqg4mZCaaSdlrR8gVP3+j4JXLjfYA/OI0Rew4zIVg6N1il10PmcBkcejzf3cDoc0nw6dPQ3o76yVuMee9NoLQzUvrBqCuTynkBQ8rAFU9mdv4Z4VXWxQJpi4O2Ipl0Ux2zHkPKc/mtKVnjo4oqu7NkYH8GvDA7PmPUvzghxaTV3ULgrYAgmesW13JTyYF/TxfsHXY7IeWZLZtvaoWeDIuCszTx/hr22iMCR+fDVBJgXxTEGrJjKQZV8A9dAdhmL6fR2i/uN1mIGhVh1EVtbhXFcc5fKDF+N/PdqJZgACx9CNIrijcqD5ed3Id1RUAbjL/78a1RACUJwNdpjArjIsyOzBatGorfgUDJuaKw== 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 Nov 2025 14:54:07 -0800 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 I think 12 digits for commit hash id is enough. > 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. > > Suggested-by: Vlastimil Babka > Signed-off-by: Joshua Hahn Acked-by: SeongJae Park Thanks, SJ [...]