Comment 3 for bug 1891931

I can confirm now hibernation can work with 5.4.0-1023, despite a harmless warning:

root@decui-tmp-2004:~# echo disk >/sys/power/state
[ 56.945758] PM: hibernation entry
[ 57.165520] Filesystems sync: 0.007 seconds
[ 57.169492] Freezing user space processes ... (elapsed 0.001 seconds) done.
[ 57.177529] OOM killer disabled.
[ 57.180702] PM: Marking nosave pages: [mem 0x00000000-0x00000fff]
[ 57.185925] PM: Marking nosave pages: [mem 0x0009f000-0x000fffff]
[ 57.191239] PM: Marking nosave pages: [mem 0x3fff0000-0xffffffff]
[ 57.197810] PM: Basic memory bitmaps created
[ 57.201563] PM: Preallocating image memory... done (allocated 210160 pages)
[ 57.623616] PM: Allocated 840640 kbytes in 0.41 seconds (2050.34 MB/s)
[ 57.629195] Freezing remaining freezable tasks ... (elapsed 0.000 seconds) done.
[ 57.637795] serial 00:04: disabled
[ 58.847939] Disabling non-boot CPUs ...
[ 58.852140] smpboot: CPU 1 is now offline
[ 58.857921] smpboot: CPU 2 is now offline
[ 58.863623] smpboot: CPU 3 is now offline
[ 58.869363] unchecked MSR access error: WRMSR to 0x40000106 (tried to write 0x412d4f49 000100ee) at rIP: 0xffffffff9ee1d9b8 (hv_cpu_die+0xe8/0x110)
[ 58.870052] Call Trace:
[ 58.870052] hv_suspend+0x5a/0x87
[ 58.870052] syscore_suspend+0x59/0x1a0
[ 58.870052] hibernation_snapshot+0x1bc/0x460
[ 58.870052] hibernate.cold+0x6d/0x1f6
[ 58.870052] state_store+0xde/0xe0
[ 58.870052] kobj_attr_store+0x12/0x20
[ 58.870052] sysfs_kf_write+0x3e/0x50
[ 58.870052] kernfs_fop_write+0xda/0x1b0
[ 58.870052] __vfs_write+0x1b/0x40
[ 58.870052] vfs_write+0xb9/0x1a0
[ 58.870052] ksys_write+0x67/0xe0
[ 58.870052] __x64_sys_write+0x1a/0x20
[ 58.870052] do_syscall_64+0x5e/0x200
[ 58.870052] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 58.870052] RIP: 0033:0x7f2f9dfcb057
[ 58.870052] Code: 64 89 02 48 c7 c0 ff ff ff ff eb bb 0f 1f 80 00 00 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
[ 58.870052] RSP: 002b:00007ffe96046608 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 58.870052] RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00007f2f9dfcb057
[ 58.870052] RDX: 0000000000000005 RSI: 000055ca5250c450 RDI: 0000000000000001
[ 58.870052] RBP: 000055ca5250c450 R08: 000000000000000a R09: 0000000000000004
[ 58.870052] R10: 000055ca50a2d017 R11: 0000000000000246 R12: 0000000000000005
[ 58.870052] R13: 00007f2f9e0a66a0 R14: 00007f2f9e0a74a0 R15: 00007f2f9e0a68a0
[ 58.870052] PM: Creating hibernation image:
[ 58.870052] PM: Need to copy 201788 pages
[ 58.870052] PM: Normal pages needed: 201788 + 1024, available pages: 3992087
[ 58.870052] PM: Hibernation image created (201788 pages copied)
[ 58.870052] Enabling non-boot CPUs ...
[ 58.870052] x86: Booting SMP configuration:
[ 58.871862] smpboot: Booting Node 0 Processor 1 APIC 0x1
[ 58.875719] CPU1 is up
[ 58.877194] smpboot: Booting Node 0 Processor 2 APIC 0x2
[ 58.881047] CPU2 is up
[ 58.882499] smpboot: Booting Node 0 Processor 3 APIC 0x3
[ 58.886033] CPU3 is up
[ 58.891099] hv_utils: KVP IC version 4.0
[ 58.893181] hv_utils: Shutdown IC version 3.2
[ 58.896580] hv_balloon: Using Dynamic Memory protocol version 2.0
[ 60.186366] hv_utils: Heartbeat IC version 3.0
[ 61.952674] hv_utils: TimeSync IC version 4.0
[ 68.108243] hv_balloon: Max. dynamic memory size: 16384 MB
[ 70.552511] serial 00:03: activated
[ 70.620778] serial 00:04: activated
[ 70.692760] PM: Using 3 thread(s) for compression
[ 70.716148] ata1.01: host indicates ignore ATA devices, ignored
[ 70.760736] PM: Compressing and saving image data (202183 pages)...
[ 70.760749] PM: Image saving progress: 0%
[ 70.831492] ata1.00: host indicates ignore ATA devices, ignored
[ 74.568857] PM: Image saving progress: 10%
[ 89.707652] PM: Image saving progress: 20%
[ 109.659651] PM: Image saving progress: 30%
[ 125.565315] PM: Image saving progress: 40%
[ 140.112605] PM: Image saving progress: 50%
[ 146.074334] PM: Image saving progress: 60%
[ 152.507964] PM: Image saving progress: 70%
[ 161.068827] PM: Image saving progress: 80%
[ 170.115167] PM: Image saving progress: 90%
[ 177.616417] PM: Image saving progress: 100%
[ 178.566922] PM: Image saving done
[ 178.623924] PM: Wrote 808732 kbytes in 107.80 seconds (7.50 MB/s)
[ 178.686742] PM: S|
[ 178.791430] kvm: exiting hardware virtualization
[ 178.851852] sd 0:0:0:0: [sdb] Synchronizing SCSI cache
[ 178.913444] ACPI: Preparing to enter system sleep state S5
[ 178.975244] reboot: Power down
[ 179.043250] acpi_power_off called

This warning can be fixed by this upstream fix:
38dce4195f0d ("x86/hyperv: Properly suspend/resume reenlightenment notifications")

How to reproduce the warning: before following https://bugs.launchpad.net/ubuntu/+source/linux-azure/+bug/1880032/comments/14 to test hibernation, make sure that "lsmod" shows kvm-intel is loaded (if not, please run "modprobe kvm-intel").

IMO this patch is not urgent so it can be combined with the next kernel relesae.