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Mon, 30 Mar 2020 23:38:38 -0400 X-MC-Unique: sNsFbYK-O0GHoJvQelgsiw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 65558107ACC4; Tue, 31 Mar 2020 03:38:36 +0000 (UTC) Received: from dhcp-128-65.nay.redhat.com (ovpn-12-247.pek2.redhat.com [10.72.12.247]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 487A750BEE; Tue, 31 Mar 2020 03:38:31 +0000 (UTC) Date: Tue, 31 Mar 2020 11:38:27 +0800 From: Dave Young To: James Morse Subject: Re: [PATCH 0/3] kexec/memory_hotplug: Prevent removal and accidental use Message-ID: <20200331033827.GA83248@dhcp-128-65.nay.redhat.com> References: <20200326180730.4754-1-james.morse@arm.com> MIME-Version: 1.0 In-Reply-To: <20200326180730.4754-1-james.morse@arm.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200330_203846_139739_927DB8B7 X-CRM114-Status: GOOD ( 22.80 ) 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: Anshuman Khandual , Catalin Marinas , Bhupesh Sharma , kexec@lists.infradead.org, linux-mm@kvack.org, Eric Biederman , Andrew Morton , Will Deacon , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi James, On 03/26/20 at 06:07pm, James Morse wrote: > Hello! > > arm64 recently queued support for memory hotremove, which led to some > new corner cases for kexec. > > If the kexec segments are loaded for a removable region, that region may > be removed before kexec actually occurs. This causes the first kernel to > lockup when applying the relocations. (I've triggered this on x86 too). Does a kexec reload work for your case? If yes then I would suggest to do it in userspace, for example have a udev rule to reload kexec if needed. Actually we have a rule to restart kdump loading, but not for kexec, it sounds also need a service to load kexec, and an udev rule to reload for memory hotplug. > > The first patch adds a memory notifier for kexec so that it can refuse > to allow in-use regions to be taken offline. > > > This doesn't solve the problem for arm64, where the new kernel must > initially rely on the data structures from the first boot to describe > memory. These don't describe hotpluggable memory. > If kexec places the kernel in one of these regions, it must also provide > a DT that describes the region in which the kernel was mapped as memory. > (and somehow ensure its always present in the future...) > > To prevent this from happening accidentally with unaware user-space, > patches two and three allow arm64 to give these regions a different > name. > > This is a change in behaviour for arm64 as memory hotadd and hotremove > were added separately. > > > I haven't tried kdump. > Unaware kdump from user-space probably won't describe the hotplug > regions if the name is different, which saves us from problems if > the memory is no longer present at kdump time, but means the vmcore > is incomplete. > > > These patches are based on arm64's for-next/core branch, but can all > be merged independently. > > Thanks, > > James Morse (3): > kexec: Prevent removal of memory in use by a loaded kexec image > mm/memory_hotplug: Allow arch override of non boot memory resource > names > arm64: memory: Give hotplug memory a different resource name > > arch/arm64/include/asm/memory.h | 11 +++++++ > kernel/kexec_core.c | 56 +++++++++++++++++++++++++++++++++ > mm/memory_hotplug.c | 6 +++- > 3 files changed, 72 insertions(+), 1 deletion(-) > > -- > 2.25.1 > > > _______________________________________________ > kexec mailing list > kexec@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/kexec > Thanks Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel