PREEMPT_RT Linux kernel does not boot on pre-launched VM

[daichifukui]

Describe the bug
A Linux kernel with PREEMPT_RT configuration does not boot on top of a pre-launched VM.

Platform
UP Squared (Apollo Lake E3950)
https://up-board.org/upsquared/specifications/

For details, see:
up2.board.xml.txt

Codebase

• ACRN release 3.0.2
• Linux kernel 5.10.120-rt70-acrn-kernel-rtvm

Scenario
Hybrid

For details, see:
scenario.xml.txt

How to Reproduce
Steps to reproduce the behavior:
1 Build Pre-launched VM0 with scenario.xml and up2.board.xml given
2 Run acrn and boot Linux kernel with PREEMPT_RT on top of VM0
3 Get acrn shell and switch to console vm0
4 No output on console vm0

Expected behaviour
Linux kernel with PREEMPT_RT boots and runs smoothly on top of pre-launched VM

Actual behaviour
Linux kernel with PREEMPT_RT does not boot on top of pre-launched VM and it looks like the kernel falls into a loop or get stuck at some point while booting

Additional context 1

Zephyr.elf successfully boots on the pre-launched VM.
Note that the Linux kernel mentioned above is a bzimage.

Additional context 2

It looks like the Linux kernel on the pre-launched VM falls into a loop or get stuck at some point as the register dump shows the same values repeatedly and continuously.

Register dump with 5.10.120-rt70-acrn-kernel-rtvm

ACRN:>vcpu_dumpreg 0 0
= VM ID 0 ==== CPU ID 0========================
= RIP=0xffffffff9b0987af RSP=0x0000000000000000 RFLAGS=0x0000000000000246
= CR0=0x0000000080050033 CR2=0x0000000000000000
= CR3=0x0000000019a10000 CR4=0x00000000003506f0
= RAX=0x00000000fffb6c20 RBX=0xffffffff9a87d0a0 RCX=0x00000000fffb6c20
= RDX=0x0000000000000000 RDI=0xffffffff9b09878c RSI=0xffffffff9a872f00
= RBP=0xffffb0d34000be98 R8=0x0000000000000001 R9=0x0000000000000000
= R10=0x0000000000000001 R11=0x0000000000000010 R12=0x0000000000000000
= R13=0xffffa067819b0000 R14=0xffffffff9a869970 R15=0xffffb0d34000be28
Cannot handle user gva yet!

ACRN:>vcpu_dumpreg 0 0
= VM ID 0 ==== CPU ID 0========================
= RIP=0xffffffff9b0987ad RSP=0x0000000000000000 RFLAGS=0x0000000000000246
= CR0=0x0000000080050033 CR2=0x0000000000000000
= CR3=0x0000000019a10000 CR4=0x00000000003506f0
= RAX=0x00000000fffb6c20 RBX=0xffffffff9a87d0a0 RCX=0x00000000fffb6c20
= RDX=0x0000000000000000 RDI=0xffffffff9b09878c RSI=0xffffffff9a872f00
= RBP=0xffffb0d34000be98 R8=0x0000000000000001 R9=0x0000000000000000
= R10=0x0000000000000001 R11=0x0000000000000010 R12=0x0000000000000000
= R13=0xffffa067819b0000 R14=0xffffffff9a869970 R15=0xffffb0d34000be28
Cannot handle user gva yet!

ACRN:>vcpu_dumpreg 0 0
= VM ID 0 ==== CPU ID 0========================
= RIP=0xffffffff9b0987af RSP=0x0000000000000000 RFLAGS=0x0000000000000246
= CR0=0x0000000080050033 CR2=0x0000000000000000
= CR3=0x0000000019a10000 CR4=0x00000000003506f0
= RAX=0x00000000fffb6c20 RBX=0xffffffff9a87d0a0 RCX=0x00000000fffb6c20
= RDX=0x0000000000000000 RDI=0xffffffff9b09878c RSI=0xffffffff9a872f00
= RBP=0xffffb0d34000be98 R8=0x0000000000000001 R9=0x0000000000000000
= R10=0x0000000000000001 R11=0x0000000000000010 R12=0x0000000000000000
= R13=0xffffa067819b0000 R14=0xffffffff9a869970 R15=0xffffb0d34000be28
Cannot handle user gva yet!

[daichifukui]

Actually, the Linux kernel is booting on a pre-launched VM but there is no output on the VM0 console. We need more configuration to get some outputs on the console. See #8703 for more details.