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). Do you mean you use 'kexec -l /boot/vmlinuz-xxxx --initrd ...' to load a kernel, next you hot remove some memory regions, then you execute 'kexec -e' to trigger kexec reboot? I may not get the point clearly, but we usually do the loading and triggering of kexec-ed kernel at the same time. > > 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. Currently, we will monitor udev events of mem hot add/remove, then reload kdump kernel. That reloading is only update the elfcorehdr, because crashkernel has to be reserved during 1st kernel bootup. I don't think this will have problem. > > > 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 > >
