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 AE27DC3DA4A for ; Mon, 5 Aug 2024 13:18:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=u6yYfWO+BnGwFresy5jD+txFb00ZVjUWRgZhpgih94I=; b=agswOzwsLxfSLdiHEelCLQbL63 Laga2iswBnJoXnYa8Vmv1skkCFGKld1cQSOwJWNFygCgTUUWUzLHGGsMHkyAkjULZCqfBGXwk5HoM St+3k7zYPaEScv5GoB7Wp8HghCt//qmlfdeEvJ9iVwlBglgYDzpyaLMwHMorQc7qccpnyAA2RNd13 XFr9t04HETVc80ZrUzEp5ii3CZndaC0Ra0fboZoRXozrXb0RJZvzMdBQrjEOXcuqoOes1oPOcdE+Y xwjUqMx7stzEeTpB/Y64wCXD6CuwUajqVszVWIQjQebGQrwRpo38AJHoZiRmz3GVGrWF6RJYxcQId jY/spppQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1saxbh-0000000FvIN-0rg0; Mon, 05 Aug 2024 13:18:37 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1saxbB-0000000FvET-1qIg for linux-arm-kernel@lists.infradead.org; Mon, 05 Aug 2024 13:18:06 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id F0DEB60B96; Mon, 5 Aug 2024 13:18:03 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7B640C32782; Mon, 5 Aug 2024 13:18:02 +0000 (UTC) Date: Mon, 5 Aug 2024 14:18:00 +0100 From: Catalin Marinas To: "Russell King (Oracle)" Cc: Jinjie Ruan , bhe@redhat.com, akpm@linux-foundation.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] ARM: Support allocating crashkernel above 4G for LPAE Message-ID: References: <20240802092510.3915986-1-ruanjinjie@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240805_061805_563070_3EC97DA7 X-CRM114-Status: GOOD ( 18.65 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Aug 02, 2024 at 12:01:43PM +0100, Russell King wrote: > On Fri, Aug 02, 2024 at 05:25:10PM +0800, Jinjie Ruan wrote: > > As ARM LPAE feature support accessing memory beyond the 4G limit, define > > HAVE_ARCH_CRASHKERNEL_RESERVATION_HIGH macro to support reserving crash At least in 6.11-rc1, there's no trace of such macro anywhere. So not sure this patch has any effect (I haven't checked linux-next though). > > memory above 4G for ARM32 LPAE. > > > > No test because there is no LPAE ARM32 hardware. > > Why are you submitting patches for features you can't test? > > I'm not going to apply this without it being properly tested, because I > don't believe that this will work in the generic case. > > If the crash kernel is located in memory outside of the lower 4GiB of > address space, and there is no alias within physical address space > for that memory, then there is *no* *way* for such a kernel to boot. > > So, right now I believe this patch to be *fundamentally* wrong. Indeed. Even on arm64, we keep some crashkernel reservations in the lower parts of the memory for ZONE_DMA allocations. On arch/arm with LPAE, we could do something similar like forcing some lowmem reservation and allowing explicit allocation in the higher ranges with crashkernel=,high. We should, of course, force the kdump image placement in the lower memory. The user kexec tools must be taught to interpret this information and provide a DT accordingly to the crash kernel. -- Catalin