From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id BEDFBCFC28A for ; Tue, 15 Oct 2024 11:22:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=MWz2l/9S03xZcnl9h0vAyr7EgElAA52/SPPGteCg/AI=; b=YqIQSuQA/wfs2mqmuNDtq3IjVh MgrlDLgFIyWHgNzGUpuS+hZYFNEHb4UhTEqJj7ol9I8H4YKJDeht6gckyOPU8vVj2BYaz097WIwH8 bOdwaM91PK+kKpXNmMd9iVwYjj5Yg1slAfI24oza0NGraML2moszlThzUNcGy2fQI6PZFmSjRw7lo nCWD018lCFmnp1iqT50M+6zjGYkyL/LObXZtN/BNvPD/eVkPPAprvSVrOdGJfkRLxAWY4HsRwQFHI d/AgceO3Lj8+fcZ+0F4S5H+tPhYA607UJFVp9NmGH1Ug3B3b8b+2lDdK/ayz0nZk0NZLKoIWq2no2 Izsgo16A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1t0fdA-000000080Ph-3kCZ; Tue, 15 Oct 2024 11:22:24 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1t0fV3-00000007ylf-076n; Tue, 15 Oct 2024 11:14:02 +0000 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-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241015_041401_176178_EDE970A0 X-CRM114-Status: GOOD ( 20.04 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 >> >> >