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From: Joel Stanley <joel@jms.id.au>
Date: Wed, 24 Feb 2021 08:03:56 +0000
Message-ID: <CACPK8XdmbXK4CVfydO5yq4Qka--wT1fR-vuqFKD_rg29fAquMA@mail.gmail.com>
Subject: Re: My kexec test patches for OpenBMC
To: Bruce Mitchell <Bruce.Mitchell@ibm.com>
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On Fri, 19 Feb 2021 at 00:53, Bruce Mitchell <Bruce.Mitchell@ibm.com> wrote=
:
>
> Hello Joel,
>
> Per your request yesterday, I am emailing the details of my kexec/kdump d=
evelopment 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.ke=
rnel -dtb /tmp/tmp.BWkadwNbTf.dtb -initrd /tmp/tmp.jRpFbzfpBs.initrd -drive=
 file=3Dobmc-phosphor-image-witherspoon-tacoma.wic,if=3Dsd,format=3Draw,ind=
ex=3D2 -net nic -net user,hostfwd=3D:127.0.0.1:2222-:22,hostfwd=3D:127.0.0.=
1:2443-:443,hostname=3Dqemu -nographic -append "crashkernel=3D64M console=
=3DttyS4,115200n8 rootwait root=3DPARTLABEL=3Drofs-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=3D::2222-:22,tftp=3D/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=3D/home/kexe=
c_files/tmp.jRpFbzfpBs.initrd --dtb=3D/home/kexec_files/tmp.BWkadwNbTf.dtb =
--append=3D"earlycon console=3DttyS4,115200n8 rootwait root=3DPARTLABEL=3Dr=
ofs-a 1 maxcpus=3D1 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=3DttyS4,115200n8).

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