During KVM tests on an RPi3 I had the following kernel warning:
[ 943.484105] ------------[ cut here ]------------
[ 943.484128] WARNING: at ../arch/arm64/kvm/../../../virt/kvm/arm/mmu.c:1634
[ 943.484261] Modules linked in: vhost_net vhost macvtap macvlan tun
ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter ip_tables
x_tables af_packet br_netfilter bridge stp llc smsc95xx uas usbnet mii
usb_storage nls_iso8859_1 nls_cp437 vfat fat dwc2 usbcore usb_common
pwm_bcm2835 i2c_bcm2835 bcm2835_rng bcm2835_dma bcm2835_wdt virt_dma leds_gpio
crc32_arm64 btrfs xor raid6_pq mmc_block vc4 drm_kms_helper syscopyarea
sysfillrect sysimgblt fb_sys_fops sdhci_iproc sdhci_pltfm sdhci mmc_core drm
dm_mirror dm_region_hash dm_log dm_mod sg efivarfs
[ 943.484263]
[ 943.484274] CPU: 0 PID: 2158 Comm: worker Not tainted 4.4.87-25-default #1
[ 943.484278] Hardware name: raspberrypi rpi/rpi, BIOS 2017.09 09/13/2017
[ 943.484284] task: ffff80000a89f180 ti: ffff80000a8a4000 task.ti:
ffff80000a8a4000
[ 943.484301] PC is at kvm_age_hva_handler+0xd4/0xdc
[ 943.484310] LR is at handle_hva_to_gpa+0xb0/0xec
[ 943.484315] pc : [<ffff0000080aeb10>] lr : [<ffff0000080ad3bc>] pstate:
80000145
[ 943.484318] sp : ffff80000a8a7070
[ 943.484325] x29: ffff80000a8a7070 x28: ffff800031290800
[ 943.484332] x27: ffff7e0000530060 x26: 0000000000000000
[ 943.484339] x25: ffff00000f2a4008 x24: 0000ffff5fa00200
[ 943.484346] x23: 0000000000000000 x22: ffff0000080aea3c
[ 943.484353] x21: ffff800032bf1000 x20: 0000000007fff000
[ 943.484360] x19: ffff800032bf1000 x18: ffff80003326fbb0
[ 943.484367] x17: ffff000008811878 x16: 000000000000000e
[ 943.484373] x15: 0000000000000007 x14: 0000000000000001
[ 943.484379] x13: 0000000000000019 x12: 0000000000000033
[ 943.484386] x11: 000000000000004c x10: 0000000000000a20
[ 943.484393] x9 : ffff80000a8a4000 x8 : ffff80000a89fc00
[ 943.484399] x7 : 0000000000000000 x6 : 0000ffff5fa00000
[ 943.484405] x5 : 0000000003fff200 x4 : 0000000000000000
[ 943.484411] x3 : 0000000000000000 x2 : 0000000000000e00
[ 943.484418] x1 : 0000000007fff000 x0 : ffff0000080ad3bc
[ 943.484419]
[ 943.484422] ---[ end trace c39c6649dbe43245 ]---
[ 943.484426] Call trace:
[ 943.678473] [<ffff0000080aeb10>] kvm_age_hva_handler+0xd4/0xdc
[ 943.684393] [<ffff0000080ad3bc>] handle_hva_to_gpa+0xb0/0xec
[ 943.690136] [<ffff0000080afdec>] kvm_age_hva+0x5c/0xbc
[ 943.695350] [<ffff0000080a3274>]
kvm_mmu_notifier_clear_flush_young+0x50/0x8c
[ 943.702595] [<ffff000008227788>] __mmu_notifier_clear_flush_young+0x6c/0xa8
[ 943.709660] [<ffff00000820b91c>] page_referenced_one+0x1a8/0x1c4
[ 943.715754] [<ffff00000822a980>] rmap_walk_ksm+0x118/0x19c
[ 943.721318] [<ffff00000820cf98>] rmap_walk+0x2c4/0x2e0
[ 943.726530] [<ffff00000820d070>] page_referenced+0xbc/0x12c
[ 943.732186] [<ffff0000081e4de8>] shrink_active_list+0x1e8/0x354
[ 943.738194] [<ffff0000081e59e0>] shrink_zone_memcg+0x4f0/0x610
[ 943.744112] [<ffff0000081e5bc8>] shrink_zone+0xc8/0x27c
[ 943.749414] [<ffff0000081e61a0>] do_try_to_free_pages+0x178/0x480
[ 943.755598] [<ffff0000081e6598>] try_to_free_pages+0xf0/0x1c0
[ 943.761429] [<ffff0000081d7a50>] __alloc_pages_nodemask+0x4a4/0x9e4
[ 943.767788] [<ffff000008225c04>] alloc_pages_vma+0x240/0x264
[ 943.773531] [<ffff000008235d18>] do_huge_pmd_anonymous_page+0x11c/0x524
[ 943.780244] [<ffff0000082027d4>] handle_mm_fault+0xdf4/0x16f4
[ 943.786074] [<ffff000008099f98>] do_page_fault+0x230/0x358
[ 943.791640] [<ffff00000809a190>] do_translation_fault+0xd0/0x100
[ 943.797734] [<ffff0000080812ac>] do_mem_abort+0x54/0xb4
[ 943.803033] Exception stack(0xffff80000a8a7a70 to 0xffff80000a8a7ba0)
[ 943.809567] 7a60: 0000000000001000
0001000000000000
[ 943.817514] 7a80: ffff80000a8a7c40 ffff0000083e3490 0000000000391a51
0000000100000021
[ 943.825459] 7aa0: ffff80000a89fc00 ffff80000a8a4000 0000000000000a20
000000010000000c
[ 943.833405] 7ac0: 0000000100000017 0000000100000019 000000010000001a
0000ffff902c6508
[ 943.841350] 7ae0: ffff00000825f8b8 0000ffff90224fe8 000000000000270f
ffff00000877de54
[ 943.849295] 7b00: ffff800036f6d900 0000000000000000 0000ffff721ff800
ffff8000050b8840
[ 943.857241] 7b20: 0000000000000780 ffff80000a8a7df8 0000000000000000
0000ffff72200800
[ 943.865186] 7b40: 0000ffff72200000 f3b2f3662da720e7 75cd0ed0b6e94ee2
32251e2d9531cceb
[ 943.873130] 7b60: ac3b60d4a515a70c 72f38aca0899a7a7 b81450f6d5f5a958
0105b4f7168e539d
[ 943.881076] 7b80: e6a95f859cc0fbf8 0003190df900b2ba ffff00000824c024
0000ffff914e4f50
[ 943.889021] [<ffff000008084508>] el1_da+0x24/0x84
[ 943.893796] [<ffff0000081d08c4>] generic_file_read_iter+0x2cc/0x594
[ 943.900158] [<ffff000008287d5c>] blkdev_read_iter+0x58/0x6c
[ 943.905814] [<ffff00000824a2f0>] __vfs_read+0xe0/0x144
[ 943.911025] [<ffff00000824ac0c>] vfs_read+0x84/0x14c
[ 943.916061] [<ffff00000824c0b0>] SyS_pread64+0x8c/0xa0
[ 943.921276] [<ffff000008084e60>] __sys_trace_return+0x0/0x4
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