On 23 February 2016 at 13:16, Will Deacon <will.deacon@xxxxxxx> wrote: > On Tue, Feb 23, 2016 at 11:58:05AM +0000, Mark Rutland wrote: >> On Mon, Feb 22, 2016 at 05:58:19PM -0800, David Daney wrote: >> > From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> >> > >> > There are two problems with the UEFI stub DT memory node removal >> > routine: >> > - it deletes nodes as it traverses the tree, which happens to work >> > but is not supported, as deletion invalidates the node iterator; >> > - deleting memory nodes entirely may discard annotations in the form >> > of additional properties on the nodes. >> > >> > Since the discovery of DT memory nodes occurs strictly before the >> > UEFI init sequence, we can simply clear the memblock memory table >> > before parsing the UEFI memory map. This way, it is no longer >> > necessary to remove the nodes, so we can remove that logic from the >> > stub as well. >> >> This is a little bit scary, but I guess this works. >> >> My only concern is that when we get kexec, a subsequent kernel must also >> have EFI memory map support, or things go bad for the next EFI-aware >> kernel after that (as things like the runtime services may have been >> corrupted by the kernel in the middle). It's difficult to fix the >> general case later. >> >> A different option would be to support status="disabled" for the memory >> nodes, and ignore these in early_init_dt_scan_memory. That way a kernel >> cannot use memory without first having parsed the EFI memory map, and we >> can still get NUMA info from the disabled nodes. > > So in that case, the middle, non-EFI kernel would fail to boot? > Realistically, once you've kexec'd a non-EFI payload, I don't think you > can rely on the EFI state remaining intact for future EFI applications. > > Is this really something we should be trying to police in the kernel? > Well, we could add entries to /reserved-memory in the stub for all the regions UEFI cares about, that would probably be sufficient to fix this case. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
