Comment 0 for bug 2045223

[summary]
Fail to boot VM with console=hvc0 in VM kernel cmdline and qemu cmd -serial stdio

[Reproduce steps]
1. Boot host with Ubuntu23.10 default kernel
root@emr-111:~# uname -a
Linux emr-111 6.5.0-13-generic #13-Ubuntu SMP PREEMPT_DYNAMIC Fri Nov 3 12:16:05 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

2. Install qemu
apt install qemu-system-common=1:8.0.4+dfsg-1ubuntu3
apt install qemu-system-x86=1:8.0.4+dfsg-1ubuntu3

3. Boot VM with Ubuntu23.10 default kernel, change guest kernel cmdline in it.
Modify /boot/grub/grub.cfg, find kernel cmdline of it's default kernel:
linux /vmlinuz-6.5.0-9-generic root=UUID=fc270810-beba-4cec-a2a4-7a9a7f104ec7 ro console=tty1 console=ttyS0 ima_hash=sha384 ima_policy=critical_data
Remove "console=tty1 console=ttyS0", add "console=hvc0 earlyprintk=ttyS0,115200", it should be like:
linux /vmlinuz-6.5.0-9-generic root=UUID=fc270810-beba-4cec-a2a4-7a9a7f104ec7 ro console=hvc0 earlyprintk=ttyS0,115200 ima_hash=sha384 ima_policy=critical_data
Poweroff VM

4. Ctrl+C to kill qemu process, boot VM again with virtio-serial qemu cmd
img=/home/ubuntu-23.10.qcow2
qemu-system-x86_64 \
    -accel kvm -smp 2 -m 4G -cpu host \
    -drive file=${img},if=none,id=virtio-disk0,format=qcow2 \
    -device virtio-blk-pci,drive=virtio-disk0,bootindex=0 \
    -bios /usr/share/qemu/OVMF.fd \
    -device virtio-net-pci,netdev=nic0 -netdev user,id=nic0,hostfwd=tcp::10023-:22 \
    -chardev stdio,id=mux,mux=on,signal=off -device virtio-serial -device virtconsole,chardev=mux \
    -serial chardev:mux \
VM boot up successfully

Poweroff VM

5. Boot VM again with -serial stdio qemu cmd
img=/home/ubuntu-23.10.qcow2
qemu-system-x86_64 \
    -accel kvm -smp 2 -m 4G -cpu host \
    -drive file=${img},if=none,id=virtio-disk0,format=qcow2 \
    -device virtio-blk-pci,drive=virtio-disk0,bootindex=0 \
    -bios /usr/share/qemu/OVMF.fd \
    -device virtio-net-pci,netdev=nic0 -netdev user,id=nic0,hostfwd=tcp::10023-:22 \
    -serial stdio

Fail to boot VM, guest crash with kernel panic
......
[ 2.305104] Btrfs loaded, zoned=yes, fsverity=yes
[ 32.446015] EXT4-fs (vda1): mounted filesystem fc270810-beba-4cec-a2a4-7a9a7f104ec7 ro with ordered data mode. Quota mode: none.
[ 32.484041] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000100
[ 32.484571] CPU: 0 PID: 1 Comm: init Not tainted 6.5.0-9-generic #9-Ubuntu
[ 32.485060] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 2023.05-2+tdx1.0 11/05/2023
[ 32.485749] Call Trace:
[ 32.485948] <TASK>
[ 32.486114] dump_stack_lvl+0x48/0x70
[ 32.486406] dump_stack+0x10/0x20
[ 32.486664] panic+0x1bb/0x3a0
[ 32.486905] do_exit+0x6a1/0x6f0
[ 32.487160] ? __count_memcg_events+0x64/0xf0
[ 32.487506] do_group_exit+0x35/0x90
[ 32.487786] __x64_sys_exit_group+0x18/0x20
[ 32.488119] do_syscall_64+0x59/0x90
[ 32.488393] ? do_user_addr_fault+0x17a/0x6b0
[ 32.488732] ? exit_to_user_mode_prepare+0x30/0xb0
[ 32.489105] ? irqentry_exit_to_user_mode+0x17/0x20
[ 32.489488] ? irqentry_exit+0x43/0x50
[ 32.489776] ? exc_page_fault+0x94/0x1b0
[ 32.490081] entry_SYSCALL_64_after_hwframe+0x6e/0xd8
[ 32.490472] RIP: 0033:0x7f583c09b2ed
[ 32.490747] Code: 02 ba ff ff ff ff 89 d0 c3 0f 1f 40 00 f3 0f 1e fa 48 8b 35 1d 3b 11 00 ba e7 00 00 00 eb 07 66 0f 1f 44 00 00 f4 89 d0 0f 05 <48> 3d 00 f0 ff ff 76 f3 f7 d8 64 89 06 eb ec 0f 1f 40 00 f3 0f 1e
[ 32.492180] RSP: 002b:00007ffe86621b88 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7
[ 32.492761] RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 00007f583c09b2ed
[ 32.493306] RDX: 00000000000000e7 RSI: ffffffffffffff88 RDI: 0000000000000001
[ 32.493849] RBP: 00007ffe86621f01 R08: 000056221af7e010 R09: 0000000000000007
[ 32.494397] R10: 000056221af7ffd0 R11: 0000000000000202 R12: 0000000000000000
[ 32.494940] R13: 00007ffe86621f40 R14: 0000562219b31598 R15: 00007f583c1f8000
[ 32.495479] </TASK>
[ 32.496940] Kernel Offset: 0x30200000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
[ 32.497737] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000100 ]---

[Expected Result]
VM boot up successfully with qemu cmd -serial stdio, no output from stdio after earlyprint

[Actual Result]
guest crash with kernel panic

<Build: version, kernel>
Host/Guest OS: Ubuntu 23.10
Host kernel: 6.5.0-13-generic
Qemu:1:8.0.4+dfsg-1ubuntu3
Guest kernel:6.5.0-9-generic

<Environment: HW version, SKU#>
CPU: EMR
CPU(s): 224
Vendor ID: GenuineIntel
    CPU family: 6
    Model: 207
    Stepping: 1