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h=Date:From:To:Cc:Subject:References:In-Reply-To; b=aNTbB+EJz4n3/fVzL99OxKi/yQ7LVSH5J6kc6Jo9gU+zr3YPO5nCdRI7Zzcd6gYZv Yo/mOVlnPijDK3bwYnF7YKw8z3B7jAT31Fh5qGtC3xYdcqh1G1W+lEi8yQ0ap15uLg G50OnTuSIoXaO5drPd4o28nKQThc+FTZJqTQDYhwCYz3Ug1NZvDrAgiXRUaDRWHkId tYBF1spAr4DG+g6tzrfafOd7CnXkOHDj7qgA7jGuWmZMjVe6m3u8pRSHGmSMCd3jDn w+V2ReHymkGyG3RRc9V7uWs7OdQbfNuP0xshxE6mhTjhNrno1Jvi+P38MozjWubqgx K1ZAbQgfIDxqA== Date: Fri, 13 Nov 2026 09:54:01 -0800 From: Kees Cook To: Chris Down Cc: Vlastimil Babka , Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Marco Elver , GONG Ruiqi , Jonathan Corbet , linux-mm@kvack.org, linux-hardening@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v2 5/6] mm/slab: Support disabling KMALLOC_PARTITION_CACHES at boot Message-ID: <202611130951.3B6741770@keescook> References: <617bbfdce4fb2689c2510f0cd7f9adbb3ab8edfa.1793253633.git.chris@chrisdown.name> <202610302123.687A961@keescook> <20261113005212.556c6f234712bdfe@chrisdown.name> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261113005212.556c6f234712bdfe@chrisdown.name> X-Spam-Status: No, score=-5.8 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-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E11DD40004 X-Stat-Signature: mw7jtayj471pmrdaksy97nys9s4i3hza X-Rspam-User: X-HE-Tag: 1794592442-400924 X-HE-Meta: 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 Re67xWsc seaa8Em/OTPck7LpH5PmKXWgIGMsC+MMMz4OmZuZBKoFfxRhgkTo4lMFKSqgHOGikBFT/PA2a/XYK7ZbGaXsjVE8evFbEwmkSrQlv9TfKPtG8rXWugCYbuJbtRr599gm59RzyVyKwnwbULT9lEdevbmN9i1+iSxAg6ZnVptVk/N8ygoQt98IcGyaA39x2nUe+tyXeYEHVjANYwdAmemoW9NttbZgBoo61W4UZ8JpufTIeb6VN4SmQ9ABSV/h2fp8xICg4xjqU8XQ73Op63ciNaX81aqP5uVG8bQSfDgZZFjDhUCE= 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 Fri, Nov 13, 2026 at 12:52:12AM -0800, Chris Down wrote: > Kees Cook writes: > > Swap the ifdef for a CONFIG-controlled static branch that defaults off > > without CONFIG_KMALLOC_PARTITION_CACHES. > > I've dropped the #ifdef in v3. kmalloc_partition_enabled now defaults to > IS_ENABLED(CONFIG_KMALLOC_PARTITION_CACHES), and kmalloc_partition= is > ignored without that option, so new_kmalloc_cache() doesn't need any > #ifdef. > > I've kept it as a bool rather than a static key, for the same reason as > on 3/6: the only reader is new_kmalloc_cache(), at boot. When > partitioning is off, kmalloc_type() still picks a partition index, but > every one of them resolves to the normal cache. So the flag is never > read on the allocation path. > > The one place a static key would actually help is kmalloc_type(), where > it could skip picking a partition and go straight to KMALLOC_NORMAL. > Since kmalloc_type() is inline, that means exporting the key to modules. > That seemed like more than this series needs, but if you think it's > worth it I'm happy to add it. I'll go look at v3. The goal was both immutability after init and avoiding a branch in an allocation path. -- Kees Cook