Hi James, On 05/01/20 at 05:57pm, James Morse wrote: > On x86, the kexec payload contains a copy of the current memory map. > If memory is added or removed, this copy of the memory map becomes > stale. Getting this wrong may prevent the next kernel from booting. > The first kernel may die if it tries to re-assemble the next kernel > in memory that has been removed. > > Discard the loaded kexec image when the memory map changes, user-space > should reload it. As we have discarded in your patches thread, adding a kexec service to reload kexec should fix this. Do you mean there's still another issue that we need fix? I may not get it clearly. > > Kdump is unaffected, as it is placed within the crashkernel reserved > memory area and only uses this memory. The stale memory map may affect > generation of the vmcore, but the kdump kernel should be in a position > to validate it. > > Signed-off-by: James Morse <james.morse@xxxxxxx> > --- > This patch obsoletes: > * kexec/memory_hotplug: Prevent removal and accidental use > https://lore.kernel.org/linux-arm-kernel/20200326180730.4754-1-james.morse@xxxxxxx/ > > kernel/kexec_core.c | 40 ++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 40 insertions(+) > > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c > index c19c0dad1ebe..e1901e5bd4b5 100644 > --- a/kernel/kexec_core.c > +++ b/kernel/kexec_core.c > @@ -12,6 +12,7 @@ > #include <linux/slab.h> > #include <linux/fs.h> > #include <linux/kexec.h> > +#include <linux/memory.h> > #include <linux/mutex.h> > #include <linux/list.h> > #include <linux/highmem.h> > @@ -22,10 +23,12 @@ > #include <linux/elf.h> > #include <linux/elfcore.h> > #include <linux/utsname.h> > +#include <linux/notifier.h> > #include <linux/numa.h> > #include <linux/suspend.h> > #include <linux/device.h> > #include <linux/freezer.h> > +#include <linux/pfn.h> > #include <linux/pm.h> > #include <linux/cpu.h> > #include <linux/uaccess.h> > @@ -1219,3 +1222,40 @@ void __weak arch_kexec_protect_crashkres(void) > > void __weak arch_kexec_unprotect_crashkres(void) > {} > + > +/* > + * If the memory layout changes, any loaded kexec image should be evicted > + * as it may contain a copy of the (now stale) memory map. This also means > + * we don't need to check the memory is still present when re-assembling the > + * new kernel at machine_kexec() time. > + */ > +static int mem_change_cb(struct notifier_block *nb, unsigned long action, > + void *data) > +{ > + /* > + * Actions are either a change, or a change being cancelled. > + * A second discard for 'cancel's is harmless. > + */ > + > + mutex_lock(&kexec_mutex); > + if (kexec_image) { > + kimage_free(xchg(&kexec_image, NULL)); > + pr_warn("loaded image discarded due to memory hotplug"); > + } > + mutex_unlock(&kexec_mutex); > + > + return NOTIFY_DONE; > +} > + > +static struct notifier_block mem_change_nb = { > + .notifier_call = mem_change_cb, > +}; > + > +static int __init register_mem_change_cb(void) > +{ > + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) > + return register_memory_notifier(&mem_change_nb); > + > + return 0; > +} > +device_initcall(register_mem_change_cb); > -- > 2.26.1 > >
