On 7 November 2014 11:41, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote: > On 7 November 2014 11:16, Mark Rutland <mark.rutland at arm.com> wrote: >> On Fri, Nov 07, 2014 at 12:41:45AM +0000, Grant Likely wrote: >>> On Thu, Nov 6, 2014 at 3:08 PM, Mark Rutland <mark.rutland at arm.com> wrote: >>> > On Thu, Nov 06, 2014 at 01:56:42AM +0000, Dave Young wrote: >>> >> On 11/03/14 at 07:46pm, Mark Rutland wrote: >>> >> > On Fri, Oct 31, 2014 at 07:52:09AM +0000, Dave Young wrote: >>> >> > > Hi Geoff >>> >> > > >>> >> > > I tested your patches. The macihne is using spin-table cpu enable method >>> >> > > so I tried maxcpus=1 as you suggested. >>> >> > > >>> >> > > There's below issues for me, thoughts? >>> >> > > >>> >> > > 1. For acpi booting there's no /proc/device-tree so kexec can not find dtb >>> >> > > to use. >>> >> > >>> >> > Are you absolutely certain of this? >>> >> > >>> >> > To use ACPI, you must have booted via EFI, as the only mechanism for >>> >> > finding the ACPI tables is via EFI. If booted via EFI, the stub will >>> >> > have created a stub DTB if there is no provided DTB, to pass the command >>> >> > line and pointers to EFI data structures. This stub DTB should be >>> >> > present in the usual place. >>> >> >>> >> Mark, I used kexec-tools from Geoff's git tree, it will create dtb from procfs >>> >> maybe I can pass external dtb to kexec-tools. What you mentioned should be true >>> >> though but I have not get idea how to get the dtb which kernel is using for boot >>> >> since it is not unflattened. >>> > >>> > Ah, sorry. I see the problem now. For ACPI you don't unflatten the tree, >>> > so there's nothing to expose at in sysfs/procfs. >>> > >>> > Somehow we need to unflatten the DTB without exposing it to drivers, >>> > such that it can be exposed to userspace in the usual place but drivers >>> > don't being probing based off of it. >>> >>> Is that even necessary? If the tree isn't unflattened, then it is just >>> a stub tree. There really isn't anything interesting in it. >> >> We need to UEFI properties [1] from /chosen to access the memory map and >> system table (both of which are necessary to access any ACPI tables). >> >>> Kexec should recreate the tree from scratch in that case. >> >> I'm not sure if the required information is exposed to userspace >> elsewhere. Ard, Leif? >> > > Personally, I think we should not be using /proc/device-tree at all, > but instead retain the original blob in some way and expose that. > > We already have /sys/firmware/efi/systab which contains the physical > addresses of the UEFI configuration tables. We should probably add an > entry for the FDT there anyway, but we would still be looking at > mmap(/dev/mem) to access it, which is not a practice we want to > encourage, I suppose. > Nah, strike that. The configuration table entry contains the original fdt, so with the device nodes etc still present. The stub makes changes to the DTB, and /that/ is the version we want to retain so subsequent kexec reboots can use it. > Also, we *must* take the secure boot scenario into account. Booting > with an arbitrary user generated DTB is nice, but if you are doing > kexec without an initrd, for instance, it would also be nice if we > could just reuse the existing DTB without bothering the user for it at > all, which would be something we could also allow when running > securely. > > -- > Ard.
