Ard, Ganapatrao, the below is something we need to consider for the combination of the NUMA & kexec approaches. It only becomes a problem if/when we preserve DT memory nodes in the presence of EFI, though it would be nice to not box ourselves into a corner. On Wed, Jan 20, 2016 at 12:02:58PM +0000, Mark Rutland wrote: > On Wed, Jan 20, 2016 at 02:25:07PM +0900, AKASHI Takahiro wrote: > > On 01/19/2016 11:01 PM, Mark Rutland wrote: > > >For NUMA topology in !ACPI kernels, we might need to also retain and > > >parse memory nodes, but only for toplogy information. The kernel would > > >still only use memory as described by the EFI memory map. > > > > > >There's a horrible edge case I've spotted if performing a chain of > > >cross-endian kexecs: LE -> BE -> LE, as the BE kernel would have to > > >respect the EFI memory map so as to avoid corrupting it for the > > >subsequent LE kernel. Other than this I believe everything should just > > >work. > > > > BE kernel doesn't support UEFI yet and cannot access UEFI memmap table. So, > > for LE -> BE, we don't use a dtb generated from /sys/firmware/fdt (or /proc/device-tree) > > (as in the case of LE -> LE) and require users to provide a dtb file explicitly. > > As I mentioned above, the problem exists when memory nodes also exist > (for describing NUMA topology). In that case the BE kernel would try to > use the information from the memory nodes. > > > For BE -> LE, BE kernel doesn't know wther UEFI memmap table is available or not > > and so use the same (explicitly-provided) dtb (as LE -> LE in !UEFI) > > See above. The problem I imagine is: > > LE kernel - uses EFI mmap, takes NUMA information from DT memory nodes > > v kexec > > BE kernel - uses DT memory nodes > - clobbers EFI runtime regions as it sees them as available > > v kexec > > LE kernel - uses EFI mmap, takes NUMA information from DT memory nodes > - tries to call EFI runtime services, and explodes. I'm not really sure what the best approach is here, but I thought that it would be good to raise awareness of the edge-case. Mark.
