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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 002E4C35272 for ; Sat, 10 Oct 2020 23:09:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D2F1E2075E for ; Sat, 10 Oct 2020 23:09:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390335AbgJJW44 (ORCPT ); Sat, 10 Oct 2020 18:56:56 -0400 Received: from mx2.suse.de ([195.135.220.15]:48184 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732220AbgJJTnz (ORCPT ); Sat, 10 Oct 2020 15:43:55 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 08B5CACAA; Sat, 10 Oct 2020 10:53:22 +0000 (UTC) Message-ID: Subject: Re: [PATCH 1/4] of/fdt: Update zone_dma_bits when running in bcm2711 From: Nicolas Saenz Julienne To: Ard Biesheuvel , Catalin Marinas Cc: Lorenzo Pieralisi , "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 Date: Sat, 10 Oct 2020 12:53:19 +0200 In-Reply-To: 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> <20201009171051.GL23638@gaia> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-qkulNlIkIv1qKYpoJFMk" User-Agent: Evolution 3.36.5 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org --=-qkulNlIkIv1qKYpoJFMk Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sat, 2020-10-10 at 12:36 +0200, Ard Biesheuvel wrote: > On Fri, 9 Oct 2020 at 19:10, Catalin Marinas wr= ote: > > 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. > > >=20 > > > 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? S= o > > > how is this going to fix the underlying issue? > >=20 > > If zone_dma_bits is 32, ZONE_DMA32 disappears into ZONE_DMA (GFP_DMA32 > > allocations fall back to ZONE_DMA). > >=20 > > 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. > >=20 > > In a separate thread, we try to fix kdump to use allocations above 4G a= s > > a fallback but this only fixes platforms with enough RAM (and maybe it'= s > > only those platforms that care about kdump). > >=20 >=20 > One thing that strikes me as odd is that we are applying the same > shifting logic to ZONE_DMA as we are applying to ZONE_DMA32, i.e., if > DRAM starts outside of the zone, it is shifted upwards. >=20 > On a typical ARM box, this gives me >=20 > [ 0.000000] Zone ranges: > [ 0.000000] DMA [mem 0x0000000080000000-0x00000000bfffffff] > [ 0.000000] DMA32 [mem 0x00000000c0000000-0x00000000ffffffff] > [ 0.000000] Normal [mem 0x0000000100000000-0x0000000fffffffff] >=20 > i.e., the 30-bit addressable range has bit 31 set, which is weird. Yes I agree it's weird, and IMO plain useless. I sent a series this summer = to address this[1], which ultimately triggered the discussion we're having rig= ht now. Although with with your latest patch and the DT counterpart, we should be O= K. It would be weird for a HW description to define DMA constraints that are impossible to reach on that system. > I wonder if it wouldn't be better (and less problematic in the general > case) to drop this logic for ZONE_DMA, and simply let it remain empty > unless there is really some memory there. =46rom my experience, you can't have empty ZONE_DMA when enabled. Empty ZONE_DMA32 is OK though. Although I'm sure it's something that can be chang= ed. Regards, Nicolas [1] https://lkml.org/lkml/2020/8/19/1022 --=-qkulNlIkIv1qKYpoJFMk Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEErOkkGDHCg2EbPcGjlfZmHno8x/4FAl+Bkp8ACgkQlfZmHno8 x/4HlwgAg+SxWz4q20kCmC4ZyKgZB1vQ1FPqNlfr3c+mE9y3v4chake0ZAe/Nvun bMlo04GRPutBFWflDzLSbnagQjBgv8J1nmIYPdrlYFYMRPSIm/lDPwRnhas+N5Ig Qx6P9sx+zhx4cXsLsSTOwueZoEvl6d7RAirq7H8PIjxGobQQ/lvRGGvQ18Rb57m1 2AE/iIiyVf6kp47STUlfk3iRjxYUjwu0P9vqyiRutle2Gk/bCY5vghD2qzrowhMg Dx9ZOICuom2mThtLThOlfBopsVbKMWJDAlzbiC6oJPO+Z2ERrP70MGU48DK0WYn4 CpWueu0wvWdi6CWYpIyKErMPl/7kcg== =HBry -----END PGP SIGNATURE----- --=-qkulNlIkIv1qKYpoJFMk--