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 918D8D3C544 for ; Fri, 18 Oct 2024 03:02:25 +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:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=B+PqcdpWNS4u7ZHFgo8/hLkbYu5t2LAmdihHzmnrPdo=; b=KhDR87sxEmGamMJ3e/n0QCvu9y m+P1NvCEhXFo2aRsyCgAA2tGCkKX5mP+UiXyY0bpmF0vZO6XrnjG2YAxrZSZPulDXz/4Clxr5JGdN n/0ngKQYlvWSV350Ox7OwiTD507Gfe5yV2r2v1d9xylnOHu6k61qb+HYnFrIKOjprJAVqbBd8Y+Hg +FElFGcW7H0qgKH8wN5chD0SygTCr4w6jJ7kE9aWGjdrliu2QVa8abxqafyId3uUP4F7zdNgUbmEx Gf21AHyZiF2BO+aJKgLSC1OkyamP6Gt7rgt2W32rG93iJ2nvQeh5q7f01jkASa+i5tK2sXz7xItuE c1SsOGrw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1t1dFl-0000000Gjzo-3sUA; Fri, 18 Oct 2024 03:02:13 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1t1dEH-0000000Gjfo-0sAJ for linux-arm-kernel@lists.infradead.org; Fri, 18 Oct 2024 03:00:43 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1729220440; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=B+PqcdpWNS4u7ZHFgo8/hLkbYu5t2LAmdihHzmnrPdo=; b=Ycs27AlHHtHvM8ZfaiMiczYrGKD5hMS0/PN5Od2G42D4fbCU/etx175ysntQDhvGBdRKtQ WnroIgfN/ZoRyU2FQAvnX0N08fsXnheuC0cp1e+guIalEl16/FlEPxSk27meLAW2jK4Xqo lzV+nH67QWUA2LpKIY/tJqCypB0t0kk= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-256-15MAYLMPP6OTtrhbesPwiw-1; Thu, 17 Oct 2024 23:00:36 -0400 X-MC-Unique: 15MAYLMPP6OTtrhbesPwiw-1 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B5F2C195608B; Fri, 18 Oct 2024 03:00:32 +0000 (UTC) Received: from localhost (unknown [10.72.112.28]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 08F5A19560A3; Fri, 18 Oct 2024 03:00:29 +0000 (UTC) Date: Fri, 18 Oct 2024 11:00:23 +0800 From: Baoquan He To: Ryan Roberts 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 Subject: Re: [RFC PATCH v1 19/57] crash: Remove PAGE_SIZE compile-time constant assumption Message-ID: References: <20241014105514.3206191-1-ryan.roberts@arm.com> <20241014105912.3207374-1-ryan.roberts@arm.com> <20241014105912.3207374-19-ryan.roberts@arm.com> <2e561511-ab20-4aa9-9b92-bd6ac6678087@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2e561511-ab20-4aa9-9b92-bd6ac6678087@arm.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241017_200041_348310_8044DA43 X-CRM114-Status: GOOD ( 28.88 ) 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 10/15/24 at 12:13pm, Ryan Roberts wrote: > 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. Makes sense, thanks for your explanation. > > > 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 > >> > >> > > >