[PATCH 00/10] arm64 kexec kernel patches V5

[ard.biesheuvel@linaro.org (Ard Biesheuvel)]

On 7 November 2014 11:41, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> On 7 November 2014 11:16, Mark Rutland <mark.rutland@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@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.