On 7 November 2014 12:35, Mark Rutland <mark.rutland at arm.com> wrote: > On Fri, Nov 07, 2014 at 10:41:11AM +0000, Ard Biesheuvel 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. > > Grant took objection to that approach previously. > >> 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. > > We should not encourage use of /dev/mem. > Agreed. > Using /sys/firmware/efi/systab doesn't get us the memory map though, > unless that's also exposed? > The address of the memory map is in /chosen/linux,uefi-mmap-start, but -as I replied-to-self earlier- the DT UEFI configuration table does not contain the properties added by the stub, so that is not going to work anyway. >> 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. > > Secure boot has to be handled completely differently. That will require > new syscall support, in-kernel purgatory, and so on. > > That should not affect the non-secureboot cases where a user wants to > load their own DTB (or other objects) into memory for the next OS (which > might not be Linux). > OK, fair enough. So ideally, we should expose the binary blob somewhere, in a similar fashion to how config.gz is exposed, perhaps? -- Ard.
