My kexec test patches for OpenBMC

[Joel Stanley]

On Fri, 19 Feb 2021 at 00:53, Bruce Mitchell <Bruce.Mitchell at ibm.com> wrote:
>
> Hello Joel,
>
> Per your request yesterday, I am emailing the details of my kexec/kdump development efforts.

Thanks. Here's what I tested:

https://github.com/shenki/linux/commits/ast2600-kexec

>
> I am running QEMU
>
> qemu-system-arm --version
> QEMU emulator version 5.2.0 (v5.1.0-3479-g27ca38d3db)

That looks fine. I'm using cedric's tree, but anything that will boot
your kernel is fine.

> qemu-system-arm -d cpu_reset -M tacoma-bmc -kernel /tmp/tmp.y2fpdAXM1h.kernel -dtb /tmp/tmp.BWkadwNbTf.dtb -initrd /tmp/tmp.jRpFbzfpBs.initrd -drive file=obmc-phosphor-image-witherspoon-tacoma.wic,if=sd,format=raw,index=2 -net nic -net user,hostfwd=:127.0.0.1:2222-:22,hostfwd=:127.0.0.1:2443-:443,hostname=qemu -nographic -append "crashkernel=64M console=ttyS4,115200n8 rootwait root=PARTLABEL=rofs-a"

You could simplify your qemu setup if you want. Here's how I tested:

 $ qemu-system-arm -M tacoma-bmc -nographic -net nic -nic
user,hostfwd=::2222-:22,tftp=/srv/tftp/ -kernel
aspeed-g5-dev/arch/arm/boot/zImage -dtb
aspeed-g5-dev/arch/arm/boot/dts/aspeed-bmc-opp-tacoma.dtb -initrd
~/dev/kernels/misc/rootfs.cpio.xz

This uses a small initramfs with the kexec utility, and has a copy of
the kernel, initrd and dtb inside to make testing easy.

Or, if you want, you can copy files into the system over the ssh port:

I have this in my ~/.ssh/config:

Host qemu
    Hostname localhost
    Port 2222
    User root
    UserKnownHostsFile /dev/null
    StrictHostKeyChecking no

And then you can use scp like this:

scp aspeed-g5-dev/arch/arm/boot/zImage
aspeed-g5-dev/arch/arm/boot/dts/aspeed-bmc-opp-tacoma.dtb
/home/joel/dev/kernels/misc/rootfs.cpio.xz  qemu:

> From OpenBMC within QEMU I am using the following to test kexec
>
> kexec -d -l /home/kexec_files/tmp.y2fpdAXM1h.kernel --initrd=/home/kexec_files/tmp.jRpFbzfpBs.initrd --dtb=/home/kexec_files/tmp.BWkadwNbTf.dtb --append="earlycon console=ttyS4,115200n8 rootwait root=PARTLABEL=rofs-a 1 maxcpus=1 reset_devices"
> kexec -d -e

Here's how I was running it:

# kexec -l zImage --dtb aspeed-bmc-opp-tacoma.dtb --initrd rootfs.cpio.xz
# kexec -e

I haven't set a new command line, so it uses the command line from the
device tree (console=ttyS4,115200n8).

With my patch we will not get the secondary CPU:

[    0.039517] ASPEED AST2600 rev A1 (05010303)
[    0.042030] smp: Bringing up secondary CPUs ...
[    1.163950] CPU1: failed to come online
[    1.167999] smp: Brought up 1 node, 1 CPU
[    1.168164] SMP: Total of 1 processors activated (2250.00 BogoMIPS).

That should be the next step in working on the kexec patches. We want
the secondary CPU to be in a state such that the new kernel can take
control as it would in a firmware boot.

Note that this didn't require any changes to the system beyond the
kernel patch. I'm using the same defconfig as we have in the tree.

Cheers,

Joel