On 27.03.20 17:56, James Morse wrote: > Hi David, > > On 3/27/20 9:30 AM, David Hildenbrand wrote: >> On 26.03.20 19:07, James Morse wrote: >>> 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. >>> >>> Signed-off-by: James Morse <james.morse@xxxxxxx> >>> --- >>> kernel/kexec_core.c | 56 +++++++++++++++++++++++++++++++++++++++++++++ >>> 1 file changed, 56 insertions(+) >>> >>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c >>> index c19c0dad1ebe..ba1d91e868ca 100644 >>> --- a/kernel/kexec_core.c >>> +++ b/kernel/kexec_core.c > >> E.g., in kernel/kexec_core.c:kimage_alloc_pages() >> >> "SetPageReserved(pages + i);" >> >> Pages that are reserved cannot get offlined. How are you able to trigger >> that before this patch? (where is the allocation path for kexec, which >> will not set the pages reserved?) > > This sets page reserved on the memory it gets back from > alloc_pages() in kimage_alloc_pages(). This is when you load the image[0]. > > The problem I see is for the target or destination memory once you execute the > image. Once machine_kexec() runs, it tries to write to this, assuming it is > still present... Let's recap 1. You load the image. You allocate memory for e.g., the kexec kernel. The pages will be marked PG_reserved, so they cannot be offlined. 2. You do the kexec. The kexec kernel will only operate on a reserved memory region (reserved via e.g., kernel cmdline crashkernel=128M). Is it that in 2., the reserved memory region (for the crashkernel) could have been offlined in the meantime? -- Thanks, David / dhildenb
