On 01/20/2016 11:59 PM, Ard Biesheuvel wrote: > On 20 January 2016 at 13:36, Mark Rutland <mark.rutland at arm.com> wrote: >> 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. >> > > I think we should simply allow the BE kernel to deal with a UEFI > memory map. It only involves a bit of byte swapping (which I already > implemented at some point) Just from my curiosity, will runtime services be also available on BE kernel with LE uefi? -Takahiro AKASHI > It would require some minor refactoring to make the UEFI init code > separate from all the other bits, but I don't see any major issues > here >
