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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 D4130C43457 for ; Fri, 9 Oct 2020 17:10:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 986C222265 for ; Fri, 9 Oct 2020 17:10:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389939AbgJIRK5 (ORCPT ); Fri, 9 Oct 2020 13:10:57 -0400 Received: from mail.kernel.org ([198.145.29.99]:50658 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389529AbgJIRK5 (ORCPT ); Fri, 9 Oct 2020 13:10:57 -0400 Received: from gaia (unknown [95.149.105.49]) (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 8A42E22267; Fri, 9 Oct 2020 17:10:54 +0000 (UTC) Date: Fri, 9 Oct 2020 18:10:52 +0100 From: Catalin Marinas To: Ard Biesheuvel Cc: Lorenzo Pieralisi , Nicolas Saenz Julienne , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Will Deacon , Linux Kernel Mailing List , Linux Memory Management List , iommu@lists.linux-foundation.org, Rob Herring , linux-rpi-kernel@lists.infradead.org, Frank Rowand , Christoph Hellwig , Linux ARM , Robin Murphy Subject: Re: [PATCH 1/4] of/fdt: Update zone_dma_bits when running in bcm2711 Message-ID: <20201009171051.GL23638@gaia> References: <20201001172320.GQ21544@gaia> <20201002115541.GC7034@gaia> <12f33d487eabd626db4c07ded5a1447795eed355.camel@suse.de> <20201009071013.GA12208@lst.de> <513833810c15b5efeab7c3cbae1963a78c71a79f.camel@suse.de> <20201009152433.GA19953@e121166-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 09, 2020 at 06:23:06PM +0200, Ard Biesheuvel wrote: > On Fri, 9 Oct 2020 at 17:24, Lorenzo Pieralisi > wrote: > > We can move this check to IORT code and call it from arm64 if it > > can be made to work. > > Finding the smallest value in the IORT, and assigning it to > zone_dma_bits if it is < 32 should be easy. But as I understand it, > having these separate DMA and DMA32 zones is what breaks kdump, no? So > how is this going to fix the underlying issue? If zone_dma_bits is 32, ZONE_DMA32 disappears into ZONE_DMA (GFP_DMA32 allocations fall back to ZONE_DMA). kdump wants DMA-able memory and, without a 30-bit ZONE_DMA, that would be the bottom 32-bit. With the introduction of ZONE_DMA, this suddenly became 1GB. We could change kdump to allocate ZONE_DMA32 but this one may also be small as it lost 1GB to ZONE_DMA. However, the kdump kernel would need to be rebuilt without ZONE_DMA since it won't have any. IIRC (it's been a while since I looked), the kdump allocation couldn't span multiple zones. In a separate thread, we try to fix kdump to use allocations above 4G as a fallback but this only fixes platforms with enough RAM (and maybe it's only those platforms that care about kdump). -- Catalin