Linux HVM fails to start with PANIC: early exception 0x00 IP 0010:clear_page_orig+0x12/0x40 error 0

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

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Hi,

I've got a report[1] that after some update Linux HVM fails to start with the
error as in the subject. It looks to be caused by some change between
Xen 4.17.3 and 4.17.4. Here the failure is on Linux 6.6.25 (both dom0
and domU), but the 6.1.62 that worked with older Xen before, now fails
too. The full error (logged via earlyprintk=xen) is:

    [    0.009500] Using GB pages for direct mapping
    PANIC: early exception 0x00 IP 10:ffffffffb01c32e2 error 0 cr2 0xffffa08649801000
    [    0.009606] CPU: 0 PID: 0 Comm: swapper Not tainted 6.6.25-1.qubes.fc37.x86_64 #1
    [    0.009665] Hardware name: Xen HVM domU, BIOS 4.17.4 04/26/2024
    [    0.009710] RIP: 0010:clear_page_orig+0x12/0x40
    [    0.009766] Code: 84 00 00 00 00 00 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 31 c0 b9 40 00 00 00 0f 1f 44 00 00 ff c9 <48> 89 07 48 89 47 08 48 89 47 10 48 89 47 18 48 89 47 20 48 89 47
    [    0.009862] RSP: 0000:ffffffffb0e03d58 EFLAGS: 00010016 ORIG_RAX: 0000000000000000
    [    0.009915] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 000000000000003f
    [    0.009967] RDX: 0000000000009801 RSI: 0000000000000000 RDI: ffffa08649801000
    [    0.010015] RBP: 0000000000000001 R08: 0000000000000001 R09: 6b7f283562d74b16
    [    0.010063] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
    [    0.010112] R13: 0000000000000000 R14: ffffffffb0e22a08 R15: ffffa08640000000
    [    0.010161] FS:  0000000000000000(0000) GS:ffffffffb16ea000(0000) knlGS:0000000000000000
    [    0.010214] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    [    0.010257] CR2: ffffa08649801000 CR3: 0000000008e80000 CR4: 00000000000000b0
    [    0.010310] Call Trace:
    [    0.010341]  <TASK>
    [    0.010372]  ? early_fixup_exception+0xf7/0x190
    [    0.010416]  ? early_idt_handler_common+0x2f/0x3a
    [    0.010460]  ? clear_page_orig+0x12/0x40
    [    0.010501]  ? alloc_low_pages+0xeb/0x150
    [    0.010541]  ? __kernel_physical_mapping_init+0x1d2/0x630
    [    0.010588]  ? init_memory_mapping+0x83/0x160
    [    0.010631]  ? init_mem_mapping+0x9a/0x460
    [    0.010669]  ? memblock_reserve+0x6d/0xf0
    [    0.010709]  ? setup_arch+0x796/0xf90
    [    0.010748]  ? start_kernel+0x63/0x420
    [    0.010787]  ? x86_64_start_reservations+0x18/0x30
    [    0.010828]  ? x86_64_start_kernel+0x96/0xa0
    [    0.010868]  ? secondary_startup_64_no_verify+0x18f/0x19b
    [    0.010918]  </TASK>

I'm pretty sure the exception 0 is misleading here, I don't see how it
could be #DE.

More logs (including full hypervisor log) are attached to the linked
issue.

This is on HP 240 g7, and my educated guess is it's Intel Celeron N4020
CPU. I cannot reproduce the issue on different hardware.

PVH domains seems to work.

Any ideas what could have happened here?

[1] https://github.com/QubesOS/qubes-issues/issues/9217

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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