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 14C56CD37B6 for ; Wed, 13 May 2026 10:29:10 +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-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Ht2QQ6l2QMI3jjLbrMSGg7m47Ftunylr0Q1SqunvI3Q=; b=twU/5iEyQ9gelbtHgguWiGgils WFYpZ0hs9FGPImJ2QICD6z4cV5tkGmcMcmM1UTPinDLrFE7J4VBc/QBdtLTfurvIALSFbz8Tbe1Pn 2lbhjtHTEFzJnBe0EVdhHqGqMTmilIpsqaxNIH07Ts6jsvQvLXCnf7CSXKEQl96SYdN9HqOHZmxbX 9swrs2Zxv9mfTdP5yKZNsHf6u/bCFSYWf0xbaYjIfzlcX3QP6BKQgCJx0jMT3KbflmOMfs/vRWVuZ vhiuRNY00/I1VGaf5djMp67SZFSjmzHokeROWGFuoPbw2SDzTExxDiKXETwrMqNVyymnaQUS9CSwA /mP8TJUw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wN6pr-00000002Bey-4054; Wed, 13 May 2026 10:29:03 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wN6pp-00000002BeV-2fca for linux-arm-kernel@lists.infradead.org; Wed, 13 May 2026 10:29:03 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id E1B6340A1C; Wed, 13 May 2026 10:29:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6F393C2BCB7; Wed, 13 May 2026 10:28:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778668140; bh=SMSduI5AnAM9kqchaE8jYdlaOT2npCWPyM5+zGPU3o0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=oqTXi24HsgBOAFuKC6Vi/Jw3ToZ3ix8HWddmTwJTDN0Un1xAN5BkYQzXEShkWawTo GbwdlpXAgWvDqvcNS4fj4SamaL21POucJDoSE7gUJ+y6jgqAQeAzM1iOpDyFP3dDYj RbhQq9r3uXj5eja2m/YDTvPvES31K7BtxsHNPpQukkzx1jXDmNwQs88p5AhLbZkYxo WYY1U+LSv7W2Mu8THlmQACiifeBWhl6VW8dk+ILwXNmNO/9dTqLE3RnuJo2ptdVwoS hfHoLk3RKGkwl/5TkgZ09NqeNYyFzaQwl3SN0CdD5rL7XU7NeUhJHKrDEBwv+tCA7/ ezv48qxYD1c9Q== Date: Wed, 13 May 2026 13:28:51 +0300 From: Mike Rapoport To: Ard Biesheuvel Cc: Jann Horn , Ard Biesheuvel , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Will Deacon , Catalin Marinas , Mark Rutland , Ryan Roberts , Anshuman Khandual , Liz Prucka , Seth Jenkins , Kees Cook , David Hildenbrand , Andrew Morton , linux-mm@kvack.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v4 02/15] mm: Make empty_zero_page __ro_after_init Message-ID: References: <20260427153416.2103979-17-ardb+git@google.com> <20260427153416.2103979-19-ardb+git@google.com> <31252c1d-a98d-4635-ab61-ce5b649e256f@app.fastmail.com> <49d30ffe-b7e1-4b05-89e0-c3fe01348bb6@app.fastmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <49d30ffe-b7e1-4b05-89e0-c3fe01348bb6@app.fastmail.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260513_032901_730423_4B8D7521 X-CRM114-Status: GOOD ( 30.45 ) 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 Wed, May 13, 2026 at 10:53:08AM +0200, Ard Biesheuvel wrote: > > On Wed, 13 May 2026, at 10:50, Mike Rapoport wrote: > > On Tue, May 12, 2026 at 02:56:16PM +0200, Ard Biesheuvel wrote: > >> On Mon, 11 May 2026, at 16:40, Jann Horn wrote: > >> > On Mon, May 11, 2026 at 10:59 AM Ard Biesheuvel wrote: > >> >> I think we should simply do something along the lines of the below, > >> >> considering that the size of a data object tends to correlate with > >> >> its minimum alignment. > >> >> > >> >> I do find it rather puzzling that the compiler emits empty_zero_page > >> >> *after* zero_page_pfn - ideally, we'd combine the below with > >> >> -fdata-sections so that the linker sees all individual objects, but > >> >> I suspect that would create some problems elsewhere. > >> >> > >> >> > >> >> --- a/include/asm-generic/vmlinux.lds.h > >> >> +++ b/include/asm-generic/vmlinux.lds.h > >> >> @@ -452,7 +452,7 @@ > >> >> #define RO_AFTER_INIT_DATA \ > >> >> . = ALIGN(8); \ > >> >> __start_ro_after_init = .; \ > >> >> - *(.data..ro_after_init) \ > >> >> + *(SORT_BY_ALIGNMENT(.data..ro_after_init)) \ > >> > > >> > Oh, neat, I didn't realize that's possible. That seems like a nicer > >> > approach... > >> > >> Neat but rather ineffective, unfortunately. (I don't see a size > >> difference with the arm64 defconfig kernel) > >> > >> Given that empty_zero_page only ever gets its address taken, we > >> might just move it into the linker script if that requires tweaking > >> anyway. We can just place it at the start of .rodata, which is > >> already page aligned on most architectures (and will become page > >> aligned unless EMPTY_ZERO_PAGE is #define'd by the arch linker > >> script to something else) > >> > >> > >> --- a/include/asm-generic/vmlinux.lds.h > >> +++ b/include/asm-generic/vmlinux.lds.h > >> @@ -472,6 +472,17 @@ > >> #endif > >> #endif > >> > >> +#ifndef EMPTY_ZERO_PAGE > >> +#ifndef __HAVE_COLOR_ZERO_PAGE > > > > I don't think we want let architectures that don't use colored zero pages > > redefine it. > > If it will be really required we can add the ability to redefine > > EMPTY_ZERO_PAGE later. > > > > I was actually intending to add use this for arm64 in the next patch. It > already has a reserved_pg_dir in .rodata which is page-sized (i.e., up > to 64k in size) and guaranteed to remain all zeroes, so empty_zero_page > could actually be an alias for that. This is what I had in a previous > revision, before you turned the empty_zero_page definition into common > code: Works for me if from arm64 perspective that's ok :) > https://lore.kernel.org/all/20260320145934.2349881-16-ardb+git@google.com/ -- Sincerely yours, Mike.