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Thu, 11 Feb 2021 12:35:59 +0000 (UTC) Received: from [10.36.114.52] (ovpn-114-52.ams2.redhat.com [10.36.114.52]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3616360BF1; Thu, 11 Feb 2021 12:35:57 +0000 (UTC) To: Anshuman Khandual , Will Deacon References: <1612239114-28428-1-git-send-email-anshuman.khandual@arm.com> <1612239114-28428-2-git-send-email-anshuman.khandual@arm.com> <20210202123215.GA16868@willie-the-truck> <20210202123524.GB16868@willie-the-truck> <20210202125152.GC16868@willie-the-truck> <4d8f5156-8628-5531-1485-322ad92aa15c@redhat.com> <0e649f28-4d54-319d-f876-8a93870cda7f@arm.com> <20210205185552.GA23216@willie-the-truck> <20210211115354.GB29894@willie-the-truck> <23e5eb93-a39c-c68e-eac1-c5ccf9036079@arm.com> From: David Hildenbrand Organization: Red Hat GmbH Subject: Re: [PATCH V2 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory Message-ID: Date: Thu, 11 Feb 2021 13:35:56 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <23e5eb93-a39c-c68e-eac1-c5ccf9036079@arm.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210211_073606_923892_E1E31778 X-CRM114-Status: GOOD ( 27.89 ) 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-kernel@vger.kernel.org, Mike Rapoport , linux-mm@kvack.org, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , James Morse , Dan Williams , Robin Murphy , Ard Biesheuvel , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 11.02.21 13:10, Anshuman Khandual wrote: > > > On 2/11/21 5:23 PM, Will Deacon wrote: >> On Fri, Feb 05, 2021 at 06:55:53PM +0000, Will Deacon wrote: >>> On Wed, Feb 03, 2021 at 09:20:39AM +0530, Anshuman Khandual wrote: >>>> On 2/2/21 6:26 PM, David Hildenbrand wrote: >>>>> On 02.02.21 13:51, Will Deacon wrote: >>>>>> On Tue, Feb 02, 2021 at 01:39:29PM +0100, David Hildenbrand wrote: >>>>>>> As I expressed already, long term we should really get rid of the arm64 >>>>>>> variant and rather special-case the generic one. Then we won't go out of >>>>>>> sync - just as it happened with ZONE_DEVICE handling here. >>>>>> >>>>>> Why does this have to be long term? This ZONE_DEVICE stuff could be the >>>>>> carrot on the stick :) >>>>> >>>>> Yes, I suggested to do it now, but Anshuman convinced me that doing a >>>>> simple fix upfront might be cleaner --- for example when it comes to >>>>> backporting :) >>>> >>>> Right. The current pfn_valid() breaks for ZONE_DEVICE memory and this fixes >>>> the problem in the present context which can be easily backported if required. >>>> >>>> Changing or rather overhauling the generic code with new configs as proposed >>>> earlier (which I am planning to work on subsequently) would definitely be an >>>> improvement for the current pfn_valid() situation in terms of maintainability >>>> but then it should not stop us from fixing the problem now. >>> >>> Alright, I've mulled this over a bit. I don't agree that this patch helps >>> with maintainability (quite the opposite, in fact), but perfection is the >>> enemy of the good so I'll queue the series for 5.12. However, I'll revert >>> the changes at the first sign of a problem, so please do work towards a >>> generic solution which can replace this in the medium term. >> >> ... and dropped. These patches appear to be responsible for a boot >> regression reported by CKI: > > Ahh, boot regression ? These patches only change the behaviour > for non boot memory only. > >> >> https://lore.kernel.org/r/cki.8D1CB60FEC.K6NJMEFQPV@redhat.com > > Will look into the logs and see if there is something pointing to > the problem. > It's strange. One thing I can imagine is a mis-detection of early sections. However, I don't see that happening: In sparse_init_nid(), we: 1. Initialize the memmap 2. Set SECTION_IS_EARLY | SECTION_HAS_MEM_MAP via sparse_init_one_section() Only hotplugged sections (DIMMs, dax/kmem) set SECTION_HAS_MEM_MAP without SECTION_IS_EARLY - which is correct, because these are not early. So once we know that we have valid_section() -- SECTION_HAS_MEM_MAP is set -- early_section() should be correct. Even if someone would be doing a pfn_valid() after memblocks_present()->memory_present() but before sparse_init_nid(), we should be fine (!valid_section() -> return 0). As it happens early during boot, I doubt that some NVDIMMs that get detected and added early during boot as system RAM (via dax/kmem). Are the problem. -- Thanks, David / dhildenb _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel