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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 47D78C4332F for ; Thu, 5 May 2022 02:13:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237517AbiEECRO (ORCPT ); Wed, 4 May 2022 22:17:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48254 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230027AbiEECRM (ORCPT ); Wed, 4 May 2022 22:17:12 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0C5AF473A8; Wed, 4 May 2022 19:13:34 -0700 (PDT) Received: from dggpemm500021.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Ktxxj04q0zGpXB; Thu, 5 May 2022 10:10:49 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500021.china.huawei.com (7.185.36.109) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 5 May 2022 10:13:32 +0800 Received: from [10.174.178.55] (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 5 May 2022 10:13:31 +0800 Subject: Re: [PATCH v22 5/9] arm64: kdump: Reimplement crashkernel=X To: Catalin Marinas CC: Baoquan He , Thomas Gleixner , "Ingo Molnar" , Borislav Petkov , , "H . Peter Anvin" , , Dave Young , Vivek Goyal , Eric Biederman , , Will Deacon , , Rob Herring , Frank Rowand , , Jonathan Corbet , , Randy Dunlap , Feng Zhou , Kefeng Wang , "Chen Zhou" , John Donnelly , Dave Kleikamp References: <3fc41a94-4247-40f3-14e7-f11e3001ec33@huawei.com> <23e2dcf4-4e9a-5298-d5d8-8761b0bbbe21@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: <2b48d210-855b-fbf1-e2b9-3ed0b42bcd22@huawei.com> Date: Thu, 5 May 2022 10:13:30 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/5/4 6:00, Catalin Marinas wrote: > On Fri, Apr 29, 2022 at 04:25:37PM +0800, Leizhen (ThunderTown) wrote: >> On 2022/4/29 16:02, Leizhen (ThunderTown) wrote: >>> On 2022/4/29 11:24, Baoquan He wrote: >>>> On 04/28/22 at 05:33pm, Leizhen (ThunderTown) wrote: >>>>> On 2022/4/28 11:52, Baoquan He wrote: >>>>>> On 04/28/22 at 11:40am, Baoquan He wrote: >>>>>>> On 04/27/22 at 05:04pm, Catalin Marinas wrote: >>>>>>>> There will be some difference as the 4G limit doesn't always hold for >>>>>>>> arm64 (though it's true in most cases). Anyway, we can probably simplify >>>>>>>> things a bit while following the documented behaviour: >>>>>>>> >>>>>>>> crashkernel=Y - current behaviour within ZONE_DMA >>>>>>>> crashkernel=Y,high - allocate from above ZONE_DMA >>>>>>>> crashkernel=Y,low - allocate within ZONE_DMA > [...] >>>>>>> Sorry to interrupt. Seems the ,high ,low and fallback are main concerns >>>>>>> about this version. And I have the same concerns about them which comes >>>>>>> from below points: >>>>>>> 1) we may need to take best effort to keep ,high, ,low behaviour >>>>>>> consistent on all ARCHes. Otherwise user/admin may be confused when they >>>>>>> deploy/configure kdump on different machines of different ARCHes in the >>>>>>> same LAB. I think we should try to avoid the confusion. > > I guess by all arches you mean just x86 here. Since the code is not > generic, all arches do their own stuff. > >>> OK, I plan to remove optimization, fallback and default low size, to follow the >>> suggestion of Catalin first. But there's one minor point of contention. >>> >>> 1) Both "crashkernel=X,high" and "crashkernel=X,low" must be present. >>> 2) Both "crashkernel=X,high" and "crashkernel=X,low" are present. >>> or >>> Allow "crashkernel=X,high" to be present alone. Unlike x86, the default low size is zero. >>> >>> I prefer 2), how about you? > > (2) works for me as well. We keep these simple as "expert" options and Okay, so I'll follow 2) to update the code. > allow crashkernel= to fall back to 'high' if not sufficient memory in > ZONE_DMA. That would be a slight change from the current behaviour but, > as Zhen Lei said, with the old tools it's just moving the error around, > the crashkernel wouldn't be available in either case. > >>>>>>> 2) Fallback behaviour is important to our distros. The reason is we will >>>>>>> provide default value with crashkernel=xxxM along kernel of distros. In >>>>>>> this case, we hope the reservation will succeed by all means. The ,high >>>>>>> and ,low is an option if customer likes to take with expertise. > > OK, that's good feedback. > > So, to recap, IIUC you are fine with: > > crashkernel=Y - allocate within ZONE_DMA with fallback > above with a default in ZONE_DMA (like > x86, 256M or swiotlb size) > crashkernel=Y,high - allocate from above ZONE_DMA > crashkernel=Y,low - allocate within ZONE_DMA > > 'crashkernel' overrides the high and low while the latter two can be > passed independently. > >>>>>>> After going through arm64 memory init code, I got below summary about >>>>>>> arm64_dma_phys_limit which is the first zone's upper limit. I think we >>>>>>> can make use of it to facilitate to simplify code. >>>>>>> ================================================================================ >>>>>>> DMA DMA32 NORMAL >>>>>>> 1)Raspberry Pi4 0~1G 3G~4G (above 4G) >>>>>>> 2)Normal machine 0~4G 0 (above 4G) >>>>>>> 3)Special machine (above 4G)~MAX >>>>>>> 4)No DMA|DMA32 (above 4G)~MAX >>>>> >>>>> arm64_memblock_init() >>>>> reserve_crashkernel() --------------- 0a30c53573b0 ("arm64: mm: Move reserve_crashkernel() into mem_init()") >>>> We don't need different code for this place of reservation as you are >>>> doing in this patchset, since arm64_dma_phys_limit is initialized as >>>> below. In fact, in arm64_memblock_init(), we have made memblock ready, >>>> we can initialize arm64_dma_phys_limit as memblock_end_of_DRAM(). And if >>>> memblock_start_of_DRAM() is bigger than 4G, we possibly can call >>>> reserve_crashkernel() here too. >>> >>> Yes. Maybe all the devices in this environment are 64-bit. One way I >>> know of allowing 32-bit devices to access high memory without SMMU >>> is: Set a fixed value for the upper 32 bits. In this case, the DMA >>> zone should be [phys_start, phys_start + 4G). > > We decided that this case doesn't really exists for arm64 platforms (no > need for special ZONE_DMA). > >> I just read the message of commit 791ab8b2e3 ("arm64: Ignore any DMA >> offsets in the max_zone_phys() calculation") >> >> Currently, the kernel assumes that if RAM starts above 32-bit (or >> zone_bits), there is still a ZONE_DMA/DMA32 at the bottom of the RAM and >> such constrained devices have a hardwired DMA offset. In practice, we >> haven't noticed any such hardware so let's assume that we can expand >> ZONE_DMA32 to the available memory if no RAM below 4GB. Similarly, >> ZONE_DMA is expanded to the 4GB limit if no RAM addressable by >> zone_bits. > > I think the above log is slightly confusing. If the DRAM starts above > 4G, ZONE_DMA goes to the end of DRAM. If the DRAM starts below 4G but > above the zone_bits for ZONE_DMA as specified in DT/ACPI, it pushes > ZONE_DMA to 4G. I don't remember why we did this last part, maybe in > case we get incorrect firmware tables, otherwise we could have extended > ZONE_DMA to end of DRAM. > > Zhen Lei, if we agreed on the crashkernel behaviour, could you please > post a series that does the above parsing allocation? Ignore the > optimisations, we can look at them afterwards. OK, I've changed the code before the festival, and I'll test it today. > > Thanks. > -- Regards, Zhen Lei 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 E5890C433F5 for ; Thu, 5 May 2022 02:14:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:CC:To:Subject:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=QqoCMI4YZzWZUypkAdHiMXVWC3iOxfc556y5xzSJgmA=; b=yIAwfnRKQik/1DqanO4yWCT5+H FejdmMMF5uqVJc+/A6W2rT97ciSZZSe4y/rmeJn2kKjaz9AIRMgKrPw7epPvvoJea007K2Wlr8Qba fSQMQDnMoPPR5YC5olNKe892u//4xLAT8h7bn9Wvfm0Yc29OZXx4g4A+pLyPiWUFCg4FbYuZtWd4c wgO6KqaADv7+y5lSySjhdcwKWBYmpzDiq1X94CHTFKy6z1z9CDIIxr9Ma0mJgHmdP0HTrqqBOYSSM BrD2ccBtP6NfLNng/YYEEoHPwj2FSUA2QHKfmEPgyFlIyVnklXzlK2Vi4DnLzvSH5PG4Vu0SkQuaZ 1aBWErnw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nmQzy-00DZsv-E4; Thu, 05 May 2022 02:13:46 +0000 Received: from szxga02-in.huawei.com ([45.249.212.188]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nmQzt-00DZph-4J; Thu, 05 May 2022 02:13:43 +0000 Received: from dggpemm500021.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Ktxxj04q0zGpXB; Thu, 5 May 2022 10:10:49 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500021.china.huawei.com (7.185.36.109) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 5 May 2022 10:13:32 +0800 Received: from [10.174.178.55] (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 5 May 2022 10:13:31 +0800 Subject: Re: [PATCH v22 5/9] arm64: kdump: Reimplement crashkernel=X To: Catalin Marinas CC: Baoquan He , Thomas Gleixner , "Ingo Molnar" , Borislav Petkov , , "H . Peter Anvin" , , Dave Young , Vivek Goyal , Eric Biederman , , Will Deacon , , Rob Herring , Frank Rowand , , Jonathan Corbet , , Randy Dunlap , Feng Zhou , Kefeng Wang , "Chen Zhou" , John Donnelly , Dave Kleikamp References: <3fc41a94-4247-40f3-14e7-f11e3001ec33@huawei.com> <23e2dcf4-4e9a-5298-d5d8-8761b0bbbe21@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: <2b48d210-855b-fbf1-e2b9-3ed0b42bcd22@huawei.com> Date: Thu, 5 May 2022 10:13:30 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220504_191341_543945_F7D26CBD X-CRM114-Status: GOOD ( 33.34 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2022/5/4 6:00, Catalin Marinas wrote: > On Fri, Apr 29, 2022 at 04:25:37PM +0800, Leizhen (ThunderTown) wrote: >> On 2022/4/29 16:02, Leizhen (ThunderTown) wrote: >>> On 2022/4/29 11:24, Baoquan He wrote: >>>> On 04/28/22 at 05:33pm, Leizhen (ThunderTown) wrote: >>>>> On 2022/4/28 11:52, Baoquan He wrote: >>>>>> On 04/28/22 at 11:40am, Baoquan He wrote: >>>>>>> On 04/27/22 at 05:04pm, Catalin Marinas wrote: >>>>>>>> There will be some difference as the 4G limit doesn't always hold for >>>>>>>> arm64 (though it's true in most cases). Anyway, we can probably simplify >>>>>>>> things a bit while following the documented behaviour: >>>>>>>> >>>>>>>> crashkernel=Y - current behaviour within ZONE_DMA >>>>>>>> crashkernel=Y,high - allocate from above ZONE_DMA >>>>>>>> crashkernel=Y,low - allocate within ZONE_DMA > [...] >>>>>>> Sorry to interrupt. Seems the ,high ,low and fallback are main concerns >>>>>>> about this version. And I have the same concerns about them which comes >>>>>>> from below points: >>>>>>> 1) we may need to take best effort to keep ,high, ,low behaviour >>>>>>> consistent on all ARCHes. Otherwise user/admin may be confused when they >>>>>>> deploy/configure kdump on different machines of different ARCHes in the >>>>>>> same LAB. I think we should try to avoid the confusion. > > I guess by all arches you mean just x86 here. Since the code is not > generic, all arches do their own stuff. > >>> OK, I plan to remove optimization, fallback and default low size, to follow the >>> suggestion of Catalin first. But there's one minor point of contention. >>> >>> 1) Both "crashkernel=X,high" and "crashkernel=X,low" must be present. >>> 2) Both "crashkernel=X,high" and "crashkernel=X,low" are present. >>> or >>> Allow "crashkernel=X,high" to be present alone. Unlike x86, the default low size is zero. >>> >>> I prefer 2), how about you? > > (2) works for me as well. We keep these simple as "expert" options and Okay, so I'll follow 2) to update the code. > allow crashkernel= to fall back to 'high' if not sufficient memory in > ZONE_DMA. That would be a slight change from the current behaviour but, > as Zhen Lei said, with the old tools it's just moving the error around, > the crashkernel wouldn't be available in either case. > >>>>>>> 2) Fallback behaviour is important to our distros. The reason is we will >>>>>>> provide default value with crashkernel=xxxM along kernel of distros. In >>>>>>> this case, we hope the reservation will succeed by all means. The ,high >>>>>>> and ,low is an option if customer likes to take with expertise. > > OK, that's good feedback. > > So, to recap, IIUC you are fine with: > > crashkernel=Y - allocate within ZONE_DMA with fallback > above with a default in ZONE_DMA (like > x86, 256M or swiotlb size) > crashkernel=Y,high - allocate from above ZONE_DMA > crashkernel=Y,low - allocate within ZONE_DMA > > 'crashkernel' overrides the high and low while the latter two can be > passed independently. > >>>>>>> After going through arm64 memory init code, I got below summary about >>>>>>> arm64_dma_phys_limit which is the first zone's upper limit. I think we >>>>>>> can make use of it to facilitate to simplify code. >>>>>>> ================================================================================ >>>>>>> DMA DMA32 NORMAL >>>>>>> 1)Raspberry Pi4 0~1G 3G~4G (above 4G) >>>>>>> 2)Normal machine 0~4G 0 (above 4G) >>>>>>> 3)Special machine (above 4G)~MAX >>>>>>> 4)No DMA|DMA32 (above 4G)~MAX >>>>> >>>>> arm64_memblock_init() >>>>> reserve_crashkernel() --------------- 0a30c53573b0 ("arm64: mm: Move reserve_crashkernel() into mem_init()") >>>> We don't need different code for this place of reservation as you are >>>> doing in this patchset, since arm64_dma_phys_limit is initialized as >>>> below. In fact, in arm64_memblock_init(), we have made memblock ready, >>>> we can initialize arm64_dma_phys_limit as memblock_end_of_DRAM(). And if >>>> memblock_start_of_DRAM() is bigger than 4G, we possibly can call >>>> reserve_crashkernel() here too. >>> >>> Yes. Maybe all the devices in this environment are 64-bit. One way I >>> know of allowing 32-bit devices to access high memory without SMMU >>> is: Set a fixed value for the upper 32 bits. In this case, the DMA >>> zone should be [phys_start, phys_start + 4G). > > We decided that this case doesn't really exists for arm64 platforms (no > need for special ZONE_DMA). > >> I just read the message of commit 791ab8b2e3 ("arm64: Ignore any DMA >> offsets in the max_zone_phys() calculation") >> >> Currently, the kernel assumes that if RAM starts above 32-bit (or >> zone_bits), there is still a ZONE_DMA/DMA32 at the bottom of the RAM and >> such constrained devices have a hardwired DMA offset. In practice, we >> haven't noticed any such hardware so let's assume that we can expand >> ZONE_DMA32 to the available memory if no RAM below 4GB. Similarly, >> ZONE_DMA is expanded to the 4GB limit if no RAM addressable by >> zone_bits. > > I think the above log is slightly confusing. If the DRAM starts above > 4G, ZONE_DMA goes to the end of DRAM. If the DRAM starts below 4G but > above the zone_bits for ZONE_DMA as specified in DT/ACPI, it pushes > ZONE_DMA to 4G. I don't remember why we did this last part, maybe in > case we get incorrect firmware tables, otherwise we could have extended > ZONE_DMA to end of DRAM. > > Zhen Lei, if we agreed on the crashkernel behaviour, could you please > post a series that does the above parsing allocation? Ignore the > optimisations, we can look at them afterwards. OK, I've changed the code before the festival, and I'll test it today. > > Thanks. > -- Regards, Zhen Lei _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel From mboxrd@z Thu Jan 1 00:00:00 1970 From: Leizhen (ThunderTown) Date: Thu, 5 May 2022 10:13:30 +0800 Subject: [PATCH v22 5/9] arm64: kdump: Reimplement crashkernel=X In-Reply-To: References: <3fc41a94-4247-40f3-14e7-f11e3001ec33@huawei.com> <23e2dcf4-4e9a-5298-d5d8-8761b0bbbe21@huawei.com> Message-ID: <2b48d210-855b-fbf1-e2b9-3ed0b42bcd22@huawei.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: kexec@lists.infradead.org On 2022/5/4 6:00, Catalin Marinas wrote: > On Fri, Apr 29, 2022 at 04:25:37PM +0800, Leizhen (ThunderTown) wrote: >> On 2022/4/29 16:02, Leizhen (ThunderTown) wrote: >>> On 2022/4/29 11:24, Baoquan He wrote: >>>> On 04/28/22 at 05:33pm, Leizhen (ThunderTown) wrote: >>>>> On 2022/4/28 11:52, Baoquan He wrote: >>>>>> On 04/28/22 at 11:40am, Baoquan He wrote: >>>>>>> On 04/27/22 at 05:04pm, Catalin Marinas wrote: >>>>>>>> There will be some difference as the 4G limit doesn't always hold for >>>>>>>> arm64 (though it's true in most cases). Anyway, we can probably simplify >>>>>>>> things a bit while following the documented behaviour: >>>>>>>> >>>>>>>> crashkernel=Y - current behaviour within ZONE_DMA >>>>>>>> crashkernel=Y,high - allocate from above ZONE_DMA >>>>>>>> crashkernel=Y,low - allocate within ZONE_DMA > [...] >>>>>>> Sorry to interrupt. Seems the ,high ,low and fallback are main concerns >>>>>>> about this version. And I have the same concerns about them which comes >>>>>>> from below points: >>>>>>> 1) we may need to take best effort to keep ,high, ,low behaviour >>>>>>> consistent on all ARCHes. Otherwise user/admin may be confused when they >>>>>>> deploy/configure kdump on different machines of different ARCHes in the >>>>>>> same LAB. I think we should try to avoid the confusion. > > I guess by all arches you mean just x86 here. Since the code is not > generic, all arches do their own stuff. > >>> OK, I plan to remove optimization, fallback and default low size, to follow the >>> suggestion of Catalin first. But there's one minor point of contention. >>> >>> 1) Both "crashkernel=X,high" and "crashkernel=X,low" must be present. >>> 2) Both "crashkernel=X,high" and "crashkernel=X,low" are present. >>> or >>> Allow "crashkernel=X,high" to be present alone. Unlike x86, the default low size is zero. >>> >>> I prefer 2), how about you? > > (2) works for me as well. We keep these simple as "expert" options and Okay, so I'll follow 2) to update the code. > allow crashkernel= to fall back to 'high' if not sufficient memory in > ZONE_DMA. That would be a slight change from the current behaviour but, > as Zhen Lei said, with the old tools it's just moving the error around, > the crashkernel wouldn't be available in either case. > >>>>>>> 2) Fallback behaviour is important to our distros. The reason is we will >>>>>>> provide default value with crashkernel=xxxM along kernel of distros. In >>>>>>> this case, we hope the reservation will succeed by all means. The ,high >>>>>>> and ,low is an option if customer likes to take with expertise. > > OK, that's good feedback. > > So, to recap, IIUC you are fine with: > > crashkernel=Y - allocate within ZONE_DMA with fallback > above with a default in ZONE_DMA (like > x86, 256M or swiotlb size) > crashkernel=Y,high - allocate from above ZONE_DMA > crashkernel=Y,low - allocate within ZONE_DMA > > 'crashkernel' overrides the high and low while the latter two can be > passed independently. > >>>>>>> After going through arm64 memory init code, I got below summary about >>>>>>> arm64_dma_phys_limit which is the first zone's upper limit. I think we >>>>>>> can make use of it to facilitate to simplify code. >>>>>>> ================================================================================ >>>>>>> DMA DMA32 NORMAL >>>>>>> 1)Raspberry Pi4 0~1G 3G~4G (above 4G) >>>>>>> 2)Normal machine 0~4G 0 (above 4G) >>>>>>> 3)Special machine (above 4G)~MAX >>>>>>> 4)No DMA|DMA32 (above 4G)~MAX >>>>> >>>>> arm64_memblock_init() >>>>> reserve_crashkernel() --------------- 0a30c53573b0 ("arm64: mm: Move reserve_crashkernel() into mem_init()") >>>> We don't need different code for this place of reservation as you are >>>> doing in this patchset, since arm64_dma_phys_limit is initialized as >>>> below. In fact, in arm64_memblock_init(), we have made memblock ready, >>>> we can initialize arm64_dma_phys_limit as memblock_end_of_DRAM(). And if >>>> memblock_start_of_DRAM() is bigger than 4G, we possibly can call >>>> reserve_crashkernel() here too. >>> >>> Yes. Maybe all the devices in this environment are 64-bit. One way I >>> know of allowing 32-bit devices to access high memory without SMMU >>> is: Set a fixed value for the upper 32 bits. In this case, the DMA >>> zone should be [phys_start, phys_start + 4G). > > We decided that this case doesn't really exists for arm64 platforms (no > need for special ZONE_DMA). > >> I just read the message of commit 791ab8b2e3 ("arm64: Ignore any DMA >> offsets in the max_zone_phys() calculation") >> >> Currently, the kernel assumes that if RAM starts above 32-bit (or >> zone_bits), there is still a ZONE_DMA/DMA32 at the bottom of the RAM and >> such constrained devices have a hardwired DMA offset. In practice, we >> haven't noticed any such hardware so let's assume that we can expand >> ZONE_DMA32 to the available memory if no RAM below 4GB. Similarly, >> ZONE_DMA is expanded to the 4GB limit if no RAM addressable by >> zone_bits. > > I think the above log is slightly confusing. If the DRAM starts above > 4G, ZONE_DMA goes to the end of DRAM. If the DRAM starts below 4G but > above the zone_bits for ZONE_DMA as specified in DT/ACPI, it pushes > ZONE_DMA to 4G. I don't remember why we did this last part, maybe in > case we get incorrect firmware tables, otherwise we could have extended > ZONE_DMA to end of DRAM. > > Zhen Lei, if we agreed on the crashkernel behaviour, could you please > post a series that does the above parsing allocation? Ignore the > optimisations, we can look at them afterwards. OK, I've changed the code before the festival, and I'll test it today. > > Thanks. > -- Regards, Zhen Lei