From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [to-be-updated] kexec-prevent-removal-of-memory-in-use-by-a-loaded-kexec-image.patch removed from -mm tree Date: Mon, 11 May 2020 13:31:20 -0700 Message-ID: <20200511203120.-GPOoWpwn%akpm@linux-foundation.org> References: <20200507183509.c5ef146c5aaeb118a25a39a8@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:38504 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729517AbgEKUbX (ORCPT ); Mon, 11 May 2020 16:31:23 -0400 In-Reply-To: <20200507183509.c5ef146c5aaeb118a25a39a8@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: anshuman.khandual@arm.com, bhsharma@redhat.com, catalin.marinas@arm.com, david@redhat.com, dyoung@redhat.com, ebiederm@xmission.com, james.morse@arm.com, mhocko@kernel.org, mm-commits@vger.kernel.org, piliu@redhat.com, will@kernel.org The patch titled Subject: kexec: prevent removal of memory in use by a loaded kexec image has been removed from the -mm tree. Its filename was kexec-prevent-removal-of-memory-in-use-by-a-loaded-kexec-image.patch This patch was dropped because an updated version will be merged ------------------------------------------------------ From: James Morse Subject: kexec: prevent removal of memory in use by a loaded kexec image Patch series "kexec/memory_hotplug: Prevent removal and accidental use". 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). 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. This patch (of 3): An image loaded for kexec is not stored in place, instead its segments are scattered through memory, and are re-assembled when needed. In the meantime, the target memory may have been removed. Because mm is not aware that this memory is still in use, it allows it to be removed. Add a memory notifier to prevent the removal of memory regions that overlap with a loaded kexec image segment. e.g., when triggered from the Qemu console: | kexec_core: memory region in use | memory memory32: Offline failed. Kexec allows user-space to specify the address that the kexec image should be loaded to. Because this memory may be in use, an image loaded for kexec is not stored in place, instead its segments are scattered through memory, and are re-assembled when needed. In the meantime, the target memory may have been removed. The target is described by user space during kexec_load() and that user space - right now - parses /proc/iomem to find applicable system memory. Link: http://lkml.kernel.org/r/20200326180730.4754-1-james.morse@arm.com Link: http://lkml.kernel.org/r/20200326180730.4754-2-james.morse@arm.com Signed-off-by: James Morse Cc: Eric Biederman Cc: Catalin Marinas Cc: Will Deacon Cc: Anshuman Khandual Cc: Bhupesh Sharma Cc: David Hildenbrand Cc: Michal Hocko Cc: piliu Cc: Dave Young Signed-off-by: Andrew Morton --- kernel/kexec_core.c | 56 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 56 insertions(+) --- a/kernel/kexec_core.c~kexec-prevent-removal-of-memory-in-use-by-a-loaded-kexec-image +++ a/kernel/kexec_core.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -22,10 +23,12 @@ #include #include #include +#include #include #include #include #include +#include #include #include #include @@ -1219,3 +1222,56 @@ void __weak arch_kexec_protect_crashkres void __weak arch_kexec_unprotect_crashkres(void) {} + +/* + * If user-space wants to offline memory that is in use by a loaded kexec + * image, it should unload the image first. + */ +static int mem_remove_cb(struct notifier_block *nb, unsigned long action, + void *data) +{ + int rv = NOTIFY_OK, i; + struct memory_notify *arg = data; + unsigned long pfn = arg->start_pfn; + unsigned long nr_segments, sstart, send; + unsigned long end_pfn = arg->start_pfn + arg->nr_pages; + + might_sleep(); + + if (action != MEM_GOING_OFFLINE) + return NOTIFY_DONE; + + mutex_lock(&kexec_mutex); + if (kexec_image) { + nr_segments = kexec_image->nr_segments; + + for (i = 0; i < nr_segments; i++) { + sstart = PFN_DOWN(kexec_image->segment[i].mem); + send = PFN_UP(kexec_image->segment[i].mem + + kexec_image->segment[i].memsz); + + if ((pfn <= sstart && sstart < end_pfn) || + (pfn <= send && send < end_pfn)) { + pr_warn("Memory region in use\n"); + rv = NOTIFY_BAD; + break; + } + } + } + mutex_unlock(&kexec_mutex); + + return rv; +} + +static struct notifier_block mem_remove_nb = { + .notifier_call = mem_remove_cb, +}; + +static int __init register_mem_remove_cb(void) +{ + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) + return register_memory_notifier(&mem_remove_nb); + + return 0; +} +device_initcall(register_mem_remove_cb); _ Patches currently in -mm which might be from james.morse@arm.com are mm-memory_hotplug-allow-arch-override-of-non-boot-memory-resource-names.patch arm64-memory-give-hotplug-memory-a-different-resource-name.patch