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a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1728990794; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=MWz2l/9S03xZcnl9h0vAyr7EgElAA52/SPPGteCg/AI=; b=8ZTrNtUiFfLG28YwjnBWMy8aH7cgBib3JoKjmLFEupdMQTEAjlOnsctpqZFDtWf+vcaVt9 zgk8vFLJmi7Do69zkgS6dPjHwKxN5sDGHW5lzovpf6YwVtHZVnzAZb8TiM3Yqa1+QRl2S+ HQp01tu+3EKGpNr8TNzCW8VffnHrkh0= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 011011007; Tue, 15 Oct 2024 04:14:30 -0700 (PDT) Received: from [10.57.86.207] (unknown [10.57.86.207]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 94A2A3F51B; Tue, 15 Oct 2024 04:13:57 -0700 (PDT) Message-ID: <2e561511-ab20-4aa9-9b92-bd6ac6678087@arm.com> Date: Tue, 15 Oct 2024 12:13:55 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 19/57] crash: Remove PAGE_SIZE compile-time constant assumption Content-Language: en-GB To: Baoquan He Cc: Andrew Morton , Anshuman Khandual , Ard Biesheuvel , Catalin Marinas , David Hildenbrand , Greg Marsden , Ivan Ivanov , Kalesh Singh , Marc Zyngier , Mark Rutland , Matthias Brugger , Miroslav Benes , Will Deacon , kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20241014105514.3206191-1-ryan.roberts@arm.com> <20241014105912.3207374-1-ryan.roberts@arm.com> <20241014105912.3207374-19-ryan.roberts@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 6290C40008 X-Rspamd-Server: rspam01 X-Stat-Signature: mrxtyqsafka6wksje46kd835cn4tj77m X-HE-Tag: 1728990835-612421 X-HE-Meta: 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 WBVhmTZn vMRS6g1jBg0HbaxsCVpS0Zv1ZMYvm8Yuxp+AfVIQAnD0VAZ4jkdyKdYGgpy0y8soMhSSAZ1Ml6Ljai0VlEyg0Shu+zUSTAyTI+cor1v5LbI+m0JgO9JPtQXP5ZtURVH0Ul/aIA5VsSyKu4VnzvVjLD4vaKx9PfmYvYztISWjQgwhIqONq6feg/2WxfgK3/gMUW5ZD+X/OjSC+ZgPa1Dxf5fhMIAxLPnLbRoSoaq6EvGnl4xh7D+Akv4P+Xxt0gNAXaxv4Tjgm5QAI7k/+J7ccsgy+pugq9dcsm+s6YLrHn0CKlVE= 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 15/10/2024 04:47, Baoquan He wrote: > On 10/14/24 at 11:58am, Ryan Roberts wrote: >> To prepare for supporting boot-time page size selection, refactor code >> to remove assumptions about PAGE_SIZE being compile-time constant. Code >> intended to be equivalent when compile-time page size is active. >> >> Updated BUILD_BUG_ON() to test against limit. >> >> Signed-off-by: Ryan Roberts >> --- >> >> ***NOTE*** >> Any confused maintainers may want to read the cover note here for context: >> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/ >> >> kernel/crash_core.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/crash_core.c b/kernel/crash_core.c >> index 63cf89393c6eb..978c600a47ac8 100644 >> --- a/kernel/crash_core.c >> +++ b/kernel/crash_core.c >> @@ -465,7 +465,7 @@ static int __init crash_notes_memory_init(void) >> * Break compile if size is bigger than PAGE_SIZE since crash_notes >> * definitely will be in 2 pages with that. >> */ >> - BUILD_BUG_ON(size > PAGE_SIZE); >> + BUILD_BUG_ON(size > PAGE_SIZE_MIN); > > This should be OK. While one thing which could happen is if selected size > is 64K, PAGE_SIZE_MIN is 4K, it will issue a false-positive warning when > compiling while actual it's not a problem during running. PAGE_SIZE can only ever be bigger than PAGE_SIZE_MIN if compiling a "boot-time page size" build. And in this case, you need to know that size is small enough to work with any of the boot-time selectable page sizes. Since size (=sizeof(note_buf_t)) is invariant to PAGE_SIZE, we can do this by checking against PAGE_SIZE_MIN. So I don't think this could ever lead to a false-positive. Not sure if > that could happen on arm64. Anyway, we can check the crash_notes to get > why it's so big when it really happens. So, > > Acked-by: Baoquan He Thanks! > >> >> crash_notes = __alloc_percpu(size, align); >> if (!crash_notes) { >> -- >> 2.43.0 >> >> >