Xen inside KVM on AMD: Linux HVM/PVH crashes on AP bring up

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

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Hi,

I' trying to boot Linux PVH on Xen, which is running inside KVM on AMD
hardware. As soon as secondary CPU is starting, domain crashes.
Strangely, without printing any related messages on the console. The
last message is "x86: Booting SMP configuration:".
This happens for both PVH and HVM with 2 vcpus. PVH/HVM domains with 1
vcpu works fine(*), as well as PV domains with multiple vcpus.

Using gdbsx I've managed to get the point where it crashes:

    (gdb) f 12
    #12 0xffffffff81025101 in do_error_trap (regs=0xffffc9000037fe78, error_code=-2401053088876204019, 
        str=0x40 <irq_stack_union+64> <error: Cannot access memory at address 0x40>, trapnr=6, signr=-2)
        at arch/x86/kernel/traps.c:302
    302	arch/x86/kernel/traps.c: No such file or directory.
    (gdb) p/x *regs
    $8 = {r15 = 0x0, r14 = 0x0, r13 = 0x0, r12 = 0x0, bp = 0x1, bx = 0xffff88007fd0f040, r11 = 0x0, 
      r10 = 0x0, r9 = 0x38, r8 = 0x0, ax = 0xffffffe4, cx = 0xffffffff82251e68, dx = 0x0, si = 0x96, 
      di = 0x82, orig_ax = 0xffffffffffffffff, ip = 0xffffffff81036bd3, cs = 0x10, flags = 0x10086, 
      sp = 0xffffc9000037ff20, ss = 0x0}
    (gdb) info symbol 0xffffffff81036bd3
    identify_secondary_cpu + 83 in section .text

It is BUG_ON(c == &boot_cpu_data). If I read it correctly, "c" is 0x82,
which indeed isn't &boot_cpu_data (0xffffffff8234fe00).

Any idea?

Version info:
Linux (L0, KVM): 4.4.114-42 (OpenSUSE Leap 42.3)
Xen (L1): 4.8.3
Linux dom0 (L1): 4.14.18
Linux guest: 4.14.18

(*) besides some 20s+ delay on flush_work in deferred_probe_initcall,
before actually calling deferred_probe_work_func.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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