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 X-Spam-Level: X-Spam-Status: No, score=-5.7 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 826ACC43331 for ; Mon, 30 Mar 2020 14:28:19 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 539542073B for ; Mon, 30 Mar 2020 14:28:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Dw1JAcnk"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="XNblZkoN" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 539542073B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject: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=l2mdm0lqh2GPdgURB+66zNgSS2hv5hVrIk4UUSzuL3E=; b=Dw1JAcnkf74BlF J7MUF1OvRZPJjInUadoKVBEGS0+ERtERpKshR1o93sRIxxy3LQP9EfzyrwKAhQEgeb1IruVoOLSD2 J3k0Ku71jguzg0XS8l7/RvOazK3xMJ3kZ1yGlVf2KVoTpxBOAhZbIP+QUT9Dz4gZ23wDSnvMxHftr RPJI7sGHcvTCNiQ86sjdVjEvrWGa/n+ptJ8qIiyQIuqPoxBhEpNgYBQvZQDz0Yfdv291YWCsTlpJ/ HFWeZnahZvvYv4YVzO1whJPVOywug9QrmtUi+o+JjUTFt6F2m9ycwofBqUdDiII8pE4+6y7c4YcAS kc9vvl0oZKmUNrknAPtw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jIvOg-0003mv-2t; Mon, 30 Mar 2020 14:28:14 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jIvOc-0003mH-V9 for linux-arm-kernel@lists.infradead.org; Mon, 30 Mar 2020 14:28:12 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7EE0020675; Mon, 30 Mar 2020 14:28:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585578490; bh=85ALpUpc/X35vGswsxKBqkjPj2xZrOJvnB1DddBDMZA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XNblZkoNvj7W1OGCUQTb3NYn/of4v49KGSVP5Fx5FXofPYzIQq/HG8rGv8cGqxOMV n64oS5KtVdYanc5t7/fUA+qjFQwDE1PD4mD9fPEWNohfNr2jkZuqTFi17PUO8dCjSJ l2czSpN9T4OZTp0iJoQgXk+kgUGSIePZe6ceDB3o= Date: Mon, 30 Mar 2020 15:28:06 +0100 From: Will Deacon To: Ard Biesheuvel Subject: Re: [RFC PATCH] arm64: remove CONFIG_DEBUG_ALIGN_RODATA feature Message-ID: <20200330142805.GA11312@willie-the-truck> References: <20200329141258.31172-1-ardb@kernel.org> <20200330135121.GD10633@willie-the-truck> <20200330140441.GE10633@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200330_072811_045433_D41EF812 X-CRM114-Status: GOOD ( 23.85 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Catalin Marinas , Linux ARM , kernel-hardening@lists.openwall.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Mar 30, 2020 at 04:22:24PM +0200, Ard Biesheuvel wrote: > On Mon, 30 Mar 2020 at 16:04, Will Deacon wrote: > > > > On Mon, Mar 30, 2020 at 03:53:04PM +0200, Ard Biesheuvel wrote: > > > On Mon, 30 Mar 2020 at 15:51, Will Deacon wrote: > > > > > > > > On Sun, Mar 29, 2020 at 04:12:58PM +0200, Ard Biesheuvel wrote: > > > > > When CONFIG_DEBUG_ALIGN_RODATA is enabled, kernel segments mapped with > > > > > different permissions (r-x for .text, r-- for .rodata, rw- for .data, > > > > > etc) are rounded up to 2 MiB so they can be mapped more efficiently. > > > > > In particular, it permits the segments to be mapped using level 2 > > > > > block entries when using 4k pages, which is expected to result in less > > > > > TLB pressure. > > > > > > > > > > However, the mappings for the bulk of the kernel will use level 2 > > > > > entries anyway, and the misaligned fringes are organized such that they > > > > > can take advantage of the contiguous bit, and use far fewer level 3 > > > > > entries than would be needed otherwise. > > > > > > > > > > This makes the value of this feature dubious at best, and since it is not > > > > > enabled in defconfig or in the distro configs, it does not appear to be > > > > > in wide use either. So let's just remove it. > > > > > > > > > > Signed-off-by: Ard Biesheuvel > > > > > --- > > > > > arch/arm64/Kconfig.debug | 13 ------------- > > > > > arch/arm64/include/asm/memory.h | 12 +----------- > > > > > drivers/firmware/efi/libstub/arm64-stub.c | 8 +++----- > > > > > 3 files changed, 4 insertions(+), 29 deletions(-) > > > > > > > > Acked-by: Will Deacon > > > > > > > > But I would really like to go a step further and rip out the block mapping > > > > support altogether so that we can fix non-coherent DMA aliases: > > > > > > > > https://lore.kernel.org/lkml/20200224194446.690816-1-hch@lst.de > > > > > > > > > > I'm not sure I follow - is this about mapping parts of the static > > > kernel Image for non-coherent DMA? > > > > Sorry, it's not directly related to your patch, just that if we're removing > > options relating to kernel mappings then I'd be quite keen on effectively > > forcing page-granularity on the linear map, as is currently done by default > > thanks to RODATA_FULL_DEFAULT_ENABLED, so that we can nobble cacheable > > aliases for non-coherent streaming DMA mappings by hooking into Christoph's > > series above. > > > > Right. I don't remember seeing any complaints about > RODATA_FULL_DEFAULT_ENABLED, but maybe it's too early for that. > > > This series just reminded me of it because it's another > > "off-by-default-behaviour-for-block-mappings-probably-because-of-performance- > > but-never-actually-measured" type of thing which really just gets in the > > way. > > > > Well, even though I agree that the lack of actual numbers is a bit > disturbing here, I'd hate to penalize all systems even more than they > already are (due to ARCH_KMALLOC_MINALIGN == ARCH_DMA_MINALIGN) by > adding another workaround that is only needed on devices that have > non-coherent masters. Fair enough, but I'd still like to see some numbers. If they're compelling, then we could explore something like CONFIG_OF_DMA_DEFAULT_COHERENT, but that doesn't really help the kconfig maze :( Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel