Re: domU crash when resuming from suspend - Xen 4.22

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Sat, Jul 18, 2026 at 04:03:29PM +0200, Marek Marczykowski-Górecki wrote:
> On Fri, Jul 17, 2026 at 09:22:47PM +0100, Frediano Ziglio wrote:
> > On Tue, 14 Jul 2026 at 18:12, Marek Marczykowski-Górecki
> > <marmarek@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > On Fri, Jun 19, 2026 at 01:24:09PM +0200, Marek Marczykowski-Górecki 
> > > wrote:
> > > > Hi,
> > > >
> > > > I'm continuing testing 4.22 and found this:
> > > >
> > > > When a domU is suspended (even without host suspend) it crashes on
> > > > resume with:
> > > >
> > > >     [   24.374629] BUG: kernel NULL pointer dereference, address: 
> > > > 0000000000000020
> > > >     [   24.374647] #PF: supervisor read access in kernel mode
> > > >     [   24.374657] #PF: error_code(0x0000) - not-present page
> > > >     [   24.374668] PGD 0 P4D 0
> > > >     [   24.374675] Oops: Oops: 0000 [#1] SMP NOPTI
> > > >     [   24.374685] CPU: 0 UID: 0 PID: 19 Comm: migration/0 Not tainted 
> > > > 6.18.31-1.qubes.13.fc41.x86_64 #1 PREEMPT(full)
> > > >     [   24.374705] Stopper: multi_cpu_stop+0x0/0x140 <- 
> > > > __stop_cpus.constprop.0+0x6f/0xb0
> > > >     [   24.374723] RIP: 0010:multi_cpu_stop+0x63/0x140
> > > >     [   24.374734] Code: 49 0f a3 1c 24 41 0f 92 c6 c7 44 24 04 00 00 
> > > > 00 00 31 ed 49 8d 5f 24 eb 2d 41 83 fd 02 74 6e 41 83 fd 03 74 49 f0 ff 
> > > > 0b 75 13 <41> 8b 47 20 41 8b 77 10 83 c0 01 41 89 77 24 41 89 47 20 41 
> > > > 83 fd
> > > >     [   24.374764] RSP: 0018:ffffc900000abe30 EFLAGS: 00010046
> > > >     [   24.374775] RAX: 0000000000000000 RBX: ffffc90000a13de4 RCX: 
> > > > 0000000000000404
> > > >     [   24.374790] RDX: 0000000000000040 RSI: ffffffffffffffff RDI: 
> > > > 0000000000770ef0
> > > >     [   24.374801] RBP: 0000000000000002 R08: ffffc900000abc80 R09: 
> > > > ffffc900000abc8c
> > > >     [   24.374813] R10: 0000000000000000 R11: ffff88801e81cdc0 R12: 
> > > > ffffffff81835ac0
> > > >     [   24.374825] R13: 0000000000000000 R14: 0000000000000000 R15: 
> > > > 0000000000000000
> > > >     [   24.374837] FS:  0000000000000000(0000) 
> > > > GS:ffff88809b369000(0000) knlGS:0000000000000000
> > > >     [   24.374850] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > >     [   24.374860] CR2: 0000000000000020 CR3: 000000000d6a2002 CR4: 
> > > > 0000000000770ef0
> > > >     [   24.374873] PKRU: 00000000
> > > >     [   24.374877] Call Trace:
> > > >     [   24.374884]  <TASK>
> > > >     [   24.374891]  ? __pfx_multi_cpu_stop+0x10/0x10
> > > >     [   24.374900]  cpu_stopper_thread+0xa3/0x170
> > > >     [   24.374908]  ? __pfx_smpboot_thread_fn+0x10/0x10
> > > >     [   24.374917]  smpboot_thread_fn+0xf3/0x220
> > > >     [   24.374925]  kthread+0xfc/0x240
> > > >     [   24.374933]  ? __pfx_kthread+0x10/0x10
> > > >     [   24.374940]  ? __pfx_kthread+0x10/0x10
> > > >     [   24.374949]  ret_from_fork+0x158/0x170
> > > >     [   24.374957]  ? __pfx_kthread+0x10/0x10
> > > >     [   24.374965]  ret_from_fork_asm+0x1a/0x30
> > > >     [   24.374973]  </TASK>
> > > >     [   24.374978] Modules linked in: snd_seq_dummy snd_hrtimer snd_seq 
> > > > snd_seq_device snd_timer snd soundcore cfg80211 rfkill vfat fat xenfs 
> > > > binfmt_misc nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject 
> > > > nft_ct nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables 
> > > > intel_rapl_msr intel_rapl_common intel_uncore_frequency_common 
> > > > intel_pmc_ssram_telemetry intel_vsec polyval_clmulni 
> > > > ghash_clmulni_intel xen_netfront xen_privcmd xen_gntdev xen_gntalloc 
> > > > xen_blkback xen_evtchn fuse loop nfnetlink ip_tables overlay 
> > > > xen_blkfront
> > > >     [   24.375064] CR2: 0000000000000020
> > > >     [   24.375071] ---[ end trace 0000000000000000 ]---
> > > >     [   24.375080] RIP: 0010:multi_cpu_stop+0x63/0x140
> > > >     [   24.375089] Code: 49 0f a3 1c 24 41 0f 92 c6 c7 44 24 04 00 00 
> > > > 00 00 31 ed 49 8d 5f 24 eb 2d 41 83 fd 02 74 6e 41 83 fd 03 74 49 f0 ff 
> > > > 0b 75 13 <41> 8b 47 20 41 8b 77 10 83 c0 01 41 89 77 24 41 89 47 20 41 
> > > > 83 fd
> > > >     [   24.375115] RSP: 0018:ffffc900000abe30 EFLAGS: 00010046
> > > >     [   24.375124] RAX: 0000000000000000 RBX: ffffc90000a13de4 RCX: 
> > > > 0000000000000404
> > > >     [   24.375142] RDX: 0000000000000040 RSI: ffffffffffffffff RDI: 
> > > > 0000000000770ef0
> > > >     [   24.375155] RBP: 0000000000000002 R08: ffffc900000abc80 R09: 
> > > > ffffc900000abc8c
> > > >     [   24.375170] R10: 0000000000000000 R11: ffff88801e81cdc0 R12: 
> > > > ffffffff81835ac0
> > > >     [   24.375184] R13: 0000000000000000 R14: 0000000000000000 R15: 
> > > > 0000000000000000
> > > >     [   24.375200] FS:  0000000000000000(0000) 
> > > > GS:ffff88809b369000(0000) knlGS:0000000000000000
> > > >     [   24.375214] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > >     [   24.375226] CR2: 0000000000000020 CR3: 000000000d6a2002 CR4: 
> > > > 0000000000770ef0
> > > >     [   24.375241] PKRU: 00000000
> > > >     [   24.375247] Kernel panic - not syncing: Fatal exception
> > > >     [   25.417403] Shutting down cpus with NMI
> > > >     [   25.417447] Kernel Offset: disabled
> > > >
> > > > There is no change on the Linux kernel side (neither dom0 nor domU), the
> > > > only change is updating Xen 4.19.4 -> 4.22-rc2 (seems to be already
> > > > broken on -rc1 too). This happens for both HVM and PVH domains. Haven't
> > > > tried PV domU (but dom0 survives host suspend).
> > >
> > > Any ideas?
> > >
> > 
> > Hi,
> >    not many ideas but while testing my libxenguest changes I found
> > similar failures using xl create/save/restore. But I was testing more
> > PV guests.
> > Does 4.21 work ?
> 
> It seems 4.21 also has this issue:
> https://gitlab.com/xen-project/people/marmarek/xen/-/jobs/15414211523
> But 4.20 is okay:
> https://gitlab.com/xen-project/people/marmarek/xen/-/jobs/15414227095
> 
> I guess I can bisect it further.

So, bisect says the first bad commit is:

    commit 9f892f84c27970840d255aef7e2851b762967de7
    Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Date:   Mon Dec 30 11:49:14 2024 +0000

        x86/domctl: Stop using XLAT_cpu_user_regs()

My test isn't 100% reliable, but I retested parent of this commit a
couple of times and it was good every time.

I wanted to test reverting it on top of 4.21, but there is a lot of
FRED-related work on top that makes such revert quite hard, to say the
least...

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

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