[PATCH 0/8] arm64 kexec kernel patches V7

[Grant Likely]

On Mon, Jan 26, 2015 at 5:44 PM, Catalin Marinas
<catalin.marinas at arm.com> wrote:
> Hi Geoff,
>
> On Sat, Jan 17, 2015 at 12:23:34AM +0000, Geoff Levand wrote:
>> This series adds the core support for kexec re-boots on arm64.  This v7 of the
>> series is mainly just a rebase to the latest arm64 for-next/core branch
>> (v3.19-rc4), and a few very minor changes requested for v6.
>
> I haven't looked at the series in detail before, so some of my comments
> may have already been discussed.
>
>> Several things are known to have problems on kexec re-boot:
>>
>> spin-table
>
> I think that's not too bad, for complete kexec support (SMP->SMP) we can
> require some CPU unplug mechanism and PSCI is one of them.
>
>> FIX: Upgrade system firmware to provide PSCI enable method support or add
>> missing spin-table support to the kernel.
>
> What's the missing spin-table support?
>
>> ACPI
>> ----
>>
>> PROBLEM: The kernel for ACPI based systems does not export a device tree to the
>> standard user space location of 'proc/device-tree'.  Current applications
>> expect to access device tree information from this standard location.
>>
>> WORK-AROUND: Disable ACPI in firmware, OR pass 'acpi=off' on the first stage
>> kernel command line, OR pass a user specified DTB using the kexec --dtb option.
>>
>> FIX: FIX: An interface to expose a binary device tree to user space has been
>> proposed.  User kexec utilities will need to be updated to add support for this
>> new interface.

The new interface is merged into mainline. /sys/firmware/fdt

> So the fix here is to boot the second stage kernel with dtb, which means
> that we mandate the existence of a DT file for any ACPI system. Are
> there plans to make the kexec'ed kernel reuse the ACPI tables?

Yes, the kexec'ed kernel will reuse the ACPI tables, and any other
data passed by UEFI. The DT we're talking about here is the DT
generated by the kernel's UEFI stub, and the kexec tools want access
to it so they can find the UEFI system table pointer.

g.