On 08/13/16 at 12:18am, Thiago Jung Bauermann wrote:

Hello,

This patch series implements a mechanism which allows the kernel to pass
on a buffer to the kernel that will be kexec'd. This buffer is passed
as a segment which is added to the kimage when it is being prepared
by kexec_file_load.

How the second kernel is informed of this buffer is architecture-specific.
On powerpc, this is done via the device tree, by checking
the properties /chosen/linux,kexec-handover-buffer-start and
/chosen/linux,kexec-handover-buffer-end, which is analogous to how the
kernel finds the initrd.

This is needed because the Integrity Measurement Architecture subsystem
needs to preserve its measurement list accross the kexec reboot. The
following patch series for the IMA subsystem uses this feature for that
purpose:

https://lists.infradead.org/pipermail/kexec/2016-August/016745.html

This is so that IMA can implement trusted boot support on the OpenPower
platform, because on such systems an intermediary Linux instance running
as part of the firmware is used to boot the target operating system via
kexec. Using this mechanism, IMA on this intermediary instance can
hand over to the target OS the measurements of the components that were
used to boot it.

Because there could be additional measurement events between the
kexec_file_load call and the actual reboot, IMA needs a way to update the
buffer with those additional events before rebooting. One can minimize
the interval between the kexec_file_load and the reboot syscalls, but as
small as it can be, there is always the possibility that the measurement
list will be out of date at the time of reboot.

To address this issue, this patch series also introduces
kexec_update_segment, which allows a reboot notifier to change the
contents of the image segment during the reboot process.

Patch 5 makes kimage_load_normal_segment and kexec_update_segment share
code. It's not much code that they can share though, so I'm not sure if
the result is actually better.

The last patch is not intended to be merged, it just demonstrates how
this feature can be used.

This series applies on top of v5 of the "kexec_file_load implementation
for PowerPC" patch series (which applies on top of v4.8-rc1):

https://lists.infradead.org/pipermail/kexec/2016-August/016843.html

I'm trying to review your patches, but seems I can not apply them
cleanly to mainline kernel or v4.8-rc1

Apply the kexec_file_load series failed as below on v4.8-rc1:

Applying: kexec_file: Allow arch-specific memory walking for
kexec_add_buffer
error: patch failed: include/linux/kexec.h:149
error: include/linux/kexec.h: patch does not apply
Patch failed at 0001 kexec_file: Allow arch-specific memory walking for
kexec_add_buffer
The copy of the patch that failed is found in: .git/rebase-apply/patch
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

What is the order of your patch series of the three patchset?

[PATCH v2 0/2] extend kexec_file_load system call
[PATCH v5 00/13] kexec_file_load implementation for PowerPC
[PATCH v2 0/6] kexec_file: Add buffer hand-over for the next kernel

Do they depend on other patches?

Thanks
Dave