[PATCH 00/10] arm64 kexec kernel patches V5

[Ard Biesheuvel]

On 7 November 2014 11:45, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> 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

*memory* nodes not device nodes

> changes to the DTB, and /that/ is the version we want to retain so
> subsequent kexec reboots can use it.
>

Sorry for the noise.

-- 
Ard.