QEMU TCG AMD64 error running Xen

[Stefano Stabellini]

Hi Paolo,

It has been a long time :-)  Nowadays I work on Xen on both ARM and AMD
x86, and our x86 configuration has only hardware-assisted guests (PVH
guests). Even Dom0 is hardware-assisted.

I am trying to run Xen with Dom0 as PVH guest in QEMU TCG. If I enable
KVM, it works, but with KVM disabled it does not.

Xen gets all the way to doing "vmrun" on Dom0, but then it keeps getting
VMEXITs (svm_vmexit_handler) with vmcb->exitcode=0x60, which is
VMEXIT_INTR. QEMU is executing
target/i386/tcg/system/seg_helper.c:x86_cpu_exec_interrupt with
interrupt_request == CPU_INTERRUPT_HARD.

This is my QEMU command line, I am using the staging branch:

/local/repos/qemu/build/qemu-system-x86_64 \
    -cpu EPYC-v3,+svm \
    -machine q35 \
    -smp 1 -m 4G \
    -monitor none -serial stdio \
    -nographic \
    -no-reboot \
    -device virtio-net-pci,netdev=n0 \
    -netdev user,id=n0,tftp=/local/qemu-x86/binaries,bootfile=/pxelinux.0

This is my pxelinux.0 file:

#!ipxe
  
kernel xen console=com1 dom0=pvh dom0-iommu=none dom0_mem=1G sync_console
module bzImage console=hvc0
boot

If it helps make things easier, you can even take the Xen and Linux
bzImage binaries from the Xen CI-loop:
https://gitlab.com/xen-project/hardware/xen/-/jobs/8980862961/artifacts/browse/binaries/
https://gitlab.com/xen-project/hardware/xen/-/jobs/8980862959/artifacts/browse/binaries/

Do you have any ideas of what could be the source of the problem?

Cheers,

Stefano