Re: [PATCH] target/ppc: Fix e6500 boot

["mario@locati.it" <mario@locati.it>]

>From: "Cédric Le Goater" clg@kaod.org
>To: "mario@locati.it" mario@locati.it, balaton@eik.bme.hu
>Cc: farosas@linux.ibm.com, qemu-devel@nongnu.org, qemu-ppc@nongnu.org, danielhb413@gmail.com
>Date: Mon, 10 Jan 2022 09:04:39 +0100
>Subject: Re: [PATCH] target/ppc: Fix e6500 boot
>
>Hello Mario,
> 
>> 
>> I have tried to launch a freshly compiled qemu from git master on a NXP T2080RDB devkit that has a e6500 CPU in combination with a freshly compiled kernel 5.16-rc6
>> I have Debian SID ppc64 up and running using such a kernel, and when I launch qemu to run a VM with the same debian sid for ppc64 and the same kernel using --enable-kvm I end up with a kernel panic
>> 
>> [....]
>> Run /sbin/init as init process
>> random: fast init done
>> systemd[1]: illegal instruction (4) at 3fff96562ac8 nip 3fff96562ac8 lr 3fff96562aa8 code 1 in libc-2.32.so[3fff96516000+1f7000]
>> systemd[1]: code: 60000000 38600006 9122b7e8 4801bead 60000000 60000000 8122b7e8 2c090004
>> systemd[1]: code: 40820014 39200005 60000000 9122b7e8 <00000000> 60000000 8122b7e8 2c090005
>> Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
>> Rebooting in 180 seconds..
> 
>I spend sometime looking at the kernel and QEMU and I noticed that
>TCG e6500 machines have an issue when the kernel has KVM support.
>I have limited knowledge on that topic but e6500 has extra MMU
>features that an hypervisor could use for the guest and the e6500
>emulation clearly doesn't have support for it.
> 
>In the guest, could you try with to run the KVM guest with a kernel
>without KVM support and let us know ?
> 
>Thanks,
> 
>C.

Unfortunately using a kernel with KVM disabled on the guest did not solve the problem on the NXP T2080RDB devkit, here's how qemu log ends

[...]
Loading compiled-in X.509 certificates
zswap: loaded using pool lzo/zbud
Key type ._fscrypt registered
Key type .fscrypt registered
Key type fscrypt-provisioning registered
Btrfs loaded, crc32c=crc32c-generic, zoned=no, fsverity=no
Key type encrypted registered
ALSA device list:
  #0: Virtual MIDI Card 1
EXT4-fs (vda): recovery complete
EXT4-fs (vda): mounted filesystem with ordered data mode. Opts: (null). Quota mode: none.
VFS: Mounted root (ext4 filesystem) on device 254:0.
devtmpfs: mounted
Freeing unused kernel image (initmem) memory: 460K
This architecture does not have kernel memory protection.
Run /sbin/init as init process
random: fast init done
systemd[1]: illegal instruction (4) at 3fffb412415c nip 3fffb412415c lr 3fffb412413c code 1 in libc-2.33.so[3fffb40d7000+1fe000]
systemd[1]: code: 60000000 38600006 9122b7d0 4801bf19 60000000 60000000 8122b7d0 2c090004 
systemd[1]: code: 40820014 39200005 60000000 9122b7d0 <00000000> 60000000 8122b7d0 2c090005 
Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
Rebooting in 180 seconds..


However, when using such a kernel without KVM on my x86_64 linux machine, qemu works just fine with an e6500 cpu using the following parameters
qemu-system-ppc64 -M ppce500 -cpu e6500 -m 2G -kernel uImage_5.16_no_kvm -append "root=/dev/vda rw" -drive format=qcow2,file=hdd_debian_sid_ppc64.qcow2,index=0,if=virtio -net nic -net user -vga none -nographic


Here the recompiled kernel 5.16 configuration used on the host that has KVM enable
https://repo.powerprogress.org/t2080rdb/qemu/2022-01-11_kernel_5.16_with_kvm.config
And here the compiled kernel
https://repo.powerprogress.org/t2080rdb/qemu/uImage_5.16_with_kvm

Here the recompiled kernel 5.16 configuration without KVM enabled for the guest
https://repo.powerprogress.org/t2080rdb/qemu/2022-01-11_kernel_5.16_no_kvm.config
And here the compiled kernel
https://repo.powerprogress.org/t2080rdb/qemu/uImage_5.16_no_kvm

Here the complete log of QEMU I have just recompiled today from git
https://repo.powerprogress.org/t2080rdb/qemu/2022-01-11_qemu_git_log_kernel_5.16_no_kvm_guest.txt

Cédric, I can provide you remote access (either ssh or remote desktop) to the computer with the NXP T2080 cpu for doing some debugging if you want, just drop me a private email and we will arrange the time for a session.