On Mon, Sep 21, 2026 at 09:59:02PM +0200, David Hildenbrand (Arm) wrote: > enum { > - SECTION_MARKED_PRESENT_BIT, > SECTION_HAS_MEM_MAP_BIT, > SECTION_IS_ONLINE_BIT, > SECTION_IS_EARLY_BIT, Hi David,

It seems dropping SECTION_MARKED_PRESENT_BIT shifts the other section flags down one bit. crash hardcodes SECTION_HAS_MEM_MAP as (1UL << 1) in pfn_to_map(), so it now tests SECTION_IS_ONLINE: offline and ZONE_DEVICE sections no longer resolve to a struct page. makedumpfile only checks bit 0 and is fine.

Keep bit 0 reserved, or export the bits via vmcoreinfo?

Cced kexec list. On Mon, Sep 28, 2026 at 09:28:08AM +0200, David Hildenbrand (Arm) wrote: > On 9/27/26 21:20, David Carlier wrote: >> >> Hi David, > > Hi! > >> >> It seems dropping SECTION_MARKED_PRESENT_BIT shifts the other section flags down >> one bit. crash hardcodes SECTION_HAS_MEM_MAP as (1UL << 1) in >> pfn_to_map(), so it now tests SECTION_IS_ONLINE: offline and >> ZONE_DEVICE sections no longer resolve to a struct page. makedumpfile >> only checks bit 0 and is fine. > > Thanks. To be expected when relying on kernel internals. > > Which makes me wonder why makedumpfile > (https://github.com/makedumpfile/makedumpfile) not require any such information. > >> >> Keep bit 0 reserved, or export the bits via vmcoreinfo? > We could export it, or crash can simply detect the change based on the kernel > version. I remember the latter was done in makedumpfile in the past (although we > export it). > > I can send a separate patch to export it. Thanks David. Checking kernel internals via kernel version is not a good idea due to the downstream kernels.