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 80089C6FD1C for ; Thu, 23 Mar 2023 17:26:20 +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:References: Message-ID:Subject:Cc: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=PVCAdZ7cvXsM1CoaEQDf8vSZYReeI7b2CBFm+oBOKJM=; b=sl4tHJSWe46ey5 rpMDghnHKdrncK6bNM7ivORqHd/jtZjA2VyPdQk6y3qff9/JD/JSxtZpEL2rGgCP0U3dsOvY3j/+P nEOxoR8b2sYl8EvyqrV8IsHl0/02M8xX2kDb+Lkw0g4Farb16JS1PM8Vwl0kLFXND+hAHY82MWV3i vySBnbW5qsPIu7kYm5H1wCho1j9E10JlO7XZfkgzMNfq3L9VUDqtDoBxWZSq9UrvuaOiKHmWDjEu8 xbtszj+byGQEK4TB2RK2mjTOZrusdpGcZGdwUT1YjGim4o7rkNbaGqOU6MiUzgMfyS1HbTpsMPsDb vAZQakR3PrJska/+It9g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1pfOgs-002akw-22; Thu, 23 Mar 2023 17:25:30 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1pfOgp-002ak7-09; Thu, 23 Mar 2023 17:25:28 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 9A8F662827; Thu, 23 Mar 2023 17:25:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EC4A4C433A8; Thu, 23 Mar 2023 17:25:24 +0000 (UTC) Date: Thu, 23 Mar 2023 17:25:21 +0000 From: Catalin Marinas To: Baoquan He Cc: linux-kernel@vger.kernel.org, horms@kernel.org, thunder.leizhen@huawei.com, John.p.donnelly@oracle.com, will@kernel.org, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v4] arm64: kdump: simplify the reservation behaviour of crashkernel=,high Message-ID: References: <20230306084124.300584-1-bhe@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230323_102527_167065_5445FD09 X-CRM114-Status: GOOD ( 34.54 ) 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 Mon, Mar 20, 2023 at 09:12:08PM +0800, Baoquan He wrote: > On 03/17/23 at 06:05pm, Catalin Marinas wrote: > > On Fri, Mar 17, 2023 at 11:09:13PM +0800, Baoquan He wrote: > > > In fact, what I want to achieve is we set CRASH_ADDR_LOW_MAX to 4G > > > fixedly on arm64, just like what we do on x86_64. As for RPi4 platform, > > > we leave it to crashkernel=size@offset syntax. Two reasons for this: > > > 1) crashkernel is needed on enterprise platform, such as workstation or > > > server. While RPi4 is obviously not the target. I contacted several RPi4 > > > players in Redhat and my friends, none of them ever played kdump > > > testing. If they really have to, crashkernel=size@offset is enough for > > > them to set. > > > > I'd like crashkernel=size (without @offset) on RPi4 to still do the > > right thing: a low allocation at least as we had until recently (or > > high+low where high here is maybe above 1GB). IOW, no regression for > > this crashkernel=size case. We can then change the explicit > > crashkernel=x,high to mean only above 4GB irrespective of the platform > > and crashkernel=x,low to be below arm64_dma_phys_limit. > > Since crashkernel=,high and crashkernel=size fallback was added in arm64 > recently, with my understanding, you are suggesting: > > on arm64: > RPi4: > crashkernel=size > 0~1G: low memory (no regression introduced) And, if not enough low memory, fall back to memory above 1GB (for RPi4; it would be above 4GB for any other system). > crashkernel=size,high > 0~1G: low memory | 4G~top: high memory Yes. > Other normal system: > crashkernel=size|crashkernel=size,high > 0~4G: low memory | 4G~top: high memory Yes. IOW, specifying 'high' only forces the high allocation above 4GB instead of arm64_dma_phys_limit, irrespective of the platform. If no 'high' specified search_base remains CRASH_ADDR_LOW_MAX (1GB on RPi4, 4GB for the rest). > > > 2) with the fixed CRASH_ADDR_LOW_MAX as 4G, we can easily fix the > > > problem of base page mapping for the whole linear mapping if crsahkernel= > > > is set in kernel parameter shown in [1] at bottom. > > > > That's a different problem ;). I should re-read that thread, forgot most > > of the details but I recall one of the counter arguments was that there > > isn't a strong case to unmap the crashkernel reservation. Now, if we > > place crashdump kernel image goes in the 'high' reservation, can we not > > leave the 'low' reservation mapped? We don't really care about it as it > > wouldn't have any meaningful code/data to be preserved. If the 'high' > > one goes above 4G always, we don't depend on the arm64_dma_phys_limit. > > Yes, this looks ideal. While it only works when crashkernel=,high case and > it succeeds to reserve a memory region for the specified size of crashkernel > high memory. At below, we have 4 cases of crashkernel= syntax: > > crashkernel=size > 1)first attempt: low memory under arm64_dma_phys_limit > 2)fallback: finding memory above 4G (2) should be 'finding memory above arm64_dma_phys_limit' to keep the current behaviour for RPi4. > crashkernel=size,high > 3)first attempt: finding memory above 4G > 4)fallback: low memory under arm64_dma_phys_limit Yes. > case 3) works with your suggestion. However, 1), 2), 4) all need to > defer to bootmem_init(). With these cases and different handling, > reserve_crashkernel() could be too complicated. Ah, because of the fallback below arm64_dma_phys_limit as in (4), we still can't move the full crashkernel reservation early. Well, we could do it in two steps: (a) early attempt at crashkernel reservation above 4G if 'high' was specified and we avoid mapping it if successful and (b) do the late crashkernel reservation below arm64_dma_phys_limit and skip unmapping as being too late. This way most server-like platforms would get a reservation above 4G, unmapped. > I am wondering if we can cancel the protection of crashkernel memory > region on arm64 for now. In earlier discussion, people questioned if the > protection is necessary on arm64. After comparison, I would rather take > away the protection method of crashkernel region since they try to > protect in a chance in one million , while the base page mapping for the > whole linear mapping is mitigating arm64 high end server always. This works for me. We can add the protection later for addresses above 4GB only as mentioned above. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel