Hi Eric, On Fri, Nov 22, 2019 at 02:00:22PM -0600, Eric W. Biederman wrote: > > esrt: Unsupported ESRT version 2904149718861218184. > > > > (The image is rather large at 18MiB as it has a built-in initrd.) > When did x86_64 get support for ARCH_KEEP_MEMBLOCK? I can't find it > anywhere. No, is hasn't. I temporarily hacked that in to see if it'd change anything and it did. Sorry to not be more clear about that. > Fundamentally when deciding where to place a new kernel kexec (either > user space or the in kernel kexec_file implementation) needs to be able > to ask the question which memory ares are reserved. > What the buddy > allocator does is unimportant as kexec copies memory from all over > the place and places it in the destined memory addresses at the > time of the kexec operation. > So my question is why doesn't the ESRT reservation wind up in > /proc/iomem? My guess is that the focus was that some EFI structures need to be kept around accross the life cycle of *one* running kernel and memblock_reserve() was enough for that. Marking them so they survive kexecing another kernel might just never have cropped up thus far. Ard or Matt would know. > Are you dealing with an embedded port that is being clever? I'm not an expert but think it's rather the opposite: It's just a memory area provided by EFI containing some potentially interesting information about the EFI firmware structure itself. The aim is to aid firmware upgrades. This information needs to survive kexec so the user would be able to use that information (e.g. for upgrades) after a kexec. So apart from leaving that memory untouched, I guess it could also be copied over to a staging area by kexec explicitly to be preserved across the kexec. Or it could be blanked out in such a way that the esrt driver would not find it after kexec and just be unavailable, if it's decided that you should only use data about a firmware for upgrades that you really just used to boot. I guess a bigger question could be asked whether it would actually be useful and safe for esrt to be available after kexec. > Or is there some subtle breakage now that x86 has memblock support that > /proc/iomem is no longer being properly maintained? Uuuh, let me backpaddle very hard here: x86 has not gained memblock preserve support. That was just me mucking about. Sorry. -- Thanks, Michael
