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Mon, 22 Sep 2025 12:27:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1758544030; bh=ETZgDSgeAnuggoKdC3R7s5QdUGOaFw9qEYrwj+PQwxM=; h=Subject:To:Cc:From:Date:In-Reply-To:From; b=T3S6PeR46N0y3ffZh4wlLo++iHwIpWjXiSk+l7zC2WNVttThnfCMo3M5g+UQquH3f nz33sIMaOVel3qFAgxOyeWChXXTkXan6MDnaFH6VxkOgyedxyWcKtZDXsYCgIWnN6y DHwbYgJJO/Dn/dUQWRqm6jDQiXDj792r3JtcH5ps= Subject: Patch "minmax: avoid overly complicated constant expressions in VM code" has been added to the 6.6-stable tree To: David.Laight@ACULAB.COM, David.Laight@aculab.com, Rodrigo.Siqueira@amd.com, Xinhui.Pan@amd.com, agk@redhat.com, airlied@gmail.com, akpm@linux-foundation.org, alexander.deucher@amd.com, alexandre.torgue@foss.st.com, amd-gfx@lists.freedesktop.org, andriy.shevchenko@linux.intel.com, anton.ivanov@cambridgegreys.com, arnd@kernel.org, artur.paszkiewicz@intel.com, bp@alien8.de, christian.koenig@amd.com, clm@fb.com, daniel@ffwll.ch, dave.hansen@linux.intel.com, davem@davemloft.net, dm-devel@lists.linux.dev, dmitry.torokhov@gmail.com, dri-devel@lists.freedesktop.org, dsahern@kernel.org, dsterba@suse.com, edumazet@google.com, evan.quan@amd.com, farbere@amazon.com, gregkh@linuxfoundation.org, harry.wentland@amd.com, hdegoede@redhat.com, hpa@zytor.com, ilpo.jarvinen@linux.intel.com, james.morse@arm.com, jdelvare@suse.com, jejb@linux.ibm.com, jernej.skrabec@gmail.com, joabreu@synopsys.com, johannes@sipsolutions.net, josef@toxicpanda.com, keescook@chromium.org, krzysztof.kozlowski@linaro.org, kuba@kernel.org, linus.walleij@linaro.org, l@kvack.org, inux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-staging@lists.linux.dev, linux-stm32@st-md-mailman.stormreply.com, linux-sunxi@lists.linux.dev, linux-um@lists.infradead.org, linux@rasmusvillemoes.dk, linux@roeck-us.net, lorenzo.stoakes@oracle.com, luc.vanoostenryck@gmail.com, luto@kernel.org, maarten.lankhorst@linux.intel.com, mailhol.vincent@wanadoo.fr, malattia@linux.it, markgross@kernel.org, martin.petersen@oracle.com, mchehab@kernel.org, mcoquelin.stm32@gmail.com, mhiramat@kernel.org, minchan@kernel.org, mingo@redhat.com, mkl@pengutronix.de, mripard@kernel.org, pabeni@redhat.com, peterz@infradead.org, pmladek@suse.com, qiuxu.zhuo@intel.com, richard@nod.at, rostedt@goodmis.org, rric@kernel.org, sakari.ailus@linux.intel.com, samuel@sholland.org, senozhatsky@chromium.org, shuah@kernel.org, snitzer@kernel.org, sunpeng.li@amd.com, tglx@linutronix.de, tony.luck@intel.com, torvalds@linux-foundation.org, tzimmermann@suse.de, wad@chromium.org, wens@csie.org, wg@grandegger.com, x86@kernel.org Cc: From: Date: Mon, 22 Sep 2025 14:26:59 +0200 In-Reply-To: <20250922103241.16213-2-farbere@amazon.com> Message-ID: <2025092259-oppose-platform-c13d@gregkh> MIME-Version: 1.0 Content-Type: text/plain; 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If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >From linux-staging+bounces-34536-greg=kroah.com@lists.linux.dev Mon Sep 22 12:34:42 2025 From: Eliav Farber Date: Mon, 22 Sep 2025 10:32:27 +0000 Subject: minmax: avoid overly complicated constant expressions in VM code To: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Cc: Linus Torvalds , Lorenzo Stoakes , David Laight Message-ID: <20250922103241.16213-2-farbere@amazon.com> From: Linus Torvalds [ Upstream commit 3a7e02c040b130b5545e4b115aada7bacd80a2b6 ] The minmax infrastructure is overkill for simple constants, and can cause huge expansions because those simple constants are then used by other things. For example, 'pageblock_order' is a core VM constant, but because it was implemented using 'min_t()' and all the type-checking that involves, it actually expanded to something like 2.5kB of preprocessor noise. And when that simple constant was then used inside other expansions: #define pageblock_nr_pages (1UL << pageblock_order) #define pageblock_start_pfn(pfn) ALIGN_DOWN((pfn), pageblock_nr_pages) and we then use that inside a 'max()' macro: case ISOLATE_SUCCESS: update_cached = false; last_migrated_pfn = max(cc->zone->zone_start_pfn, pageblock_start_pfn(cc->migrate_pfn - 1)); the end result was that one statement expanding to 253kB in size. There are probably other cases of this, but this one case certainly stood out. I've added 'MIN_T()' and 'MAX_T()' macros for this kind of "core simple constant with specific type" use. These macros skip the type checking, and as such need to be very sparingly used only for obvious cases that have active issues like this. Reported-by: Lorenzo Stoakes Link: https://lore.kernel.org/all/36aa2cad-1db1-4abf-8dd2-fb20484aabc3@lucifer.local/ Cc: David Laight Signed-off-by: Linus Torvalds Signed-off-by: Eliav Farber Signed-off-by: Greg Kroah-Hartman --- include/linux/minmax.h | 7 +++++++ include/linux/pageblock-flags.h | 2 +- 2 files changed, 8 insertions(+), 1 deletion(-) --- a/include/linux/minmax.h +++ b/include/linux/minmax.h @@ -270,4 +270,11 @@ static inline bool in_range32(u32 val, u #define swap(a, b) \ do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0) +/* + * Use these carefully: no type checking, and uses the arguments + * multiple times. Use for obvious constants only. + */ +#define MIN_T(type,a,b) __cmp(min,(type)(a),(type)(b)) +#define MAX_T(type,a,b) __cmp(max,(type)(a),(type)(b)) + #endif /* _LINUX_MINMAX_H */ --- a/include/linux/pageblock-flags.h +++ b/include/linux/pageblock-flags.h @@ -41,7 +41,7 @@ extern unsigned int pageblock_order; * Huge pages are a constant size, but don't exceed the maximum allocation * granularity. */ -#define pageblock_order min_t(unsigned int, HUGETLB_PAGE_ORDER, MAX_ORDER) +#define pageblock_order MIN_T(unsigned int, HUGETLB_PAGE_ORDER, MAX_ORDER) #endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */ Patches currently in stable-queue which might be from farbere@amazon.com are queue-6.6/minmax-don-t-use-max-in-situations-that-want-a-c-constant-expression.patch queue-6.6/minmax-make-generic-min-and-max-macros-available-everywhere.patch queue-6.6/minmax-fix-up-min3-and-max3-too.patch queue-6.6/minmax-add-a-few-more-min_t-max_t-users.patch queue-6.6/minmax-improve-macro-expansion-and-type-checking.patch queue-6.6/minmax-avoid-overly-complicated-constant-expressions-in-vm-code.patch queue-6.6/minmax-simplify-min-max-clamp-implementation.patch queue-6.6/minmax-simplify-and-clarify-min_t-max_t-implementation.patch