kvm splat in mmu_spte_clear_track_bits

[Adam Borowski]

Hi!
I'm afraid I keep getting a quite reliable, but random, splat when running
KVM:

------------[ cut here ]------------
WARNING: CPU: 5 PID: 5826 at arch/x86/kvm/mmu.c:717 mmu_spte_clear_track_bits+0x123/0x170
Modules linked in: tun nbd arc4 rtl8xxxu mac80211 cfg80211 rfkill nouveau video ttm
CPU: 5 PID: 5826 Comm: qemu-system-x86 Not tainted 4.13.0-rc5-vanilla-ubsan-00211-g7f680d7ec315 #1
Hardware name: System manufacturer System Product Name/M4A77T, BIOS 2401    05/18/2011
task: ffff880207ef0400 task.stack: ffffc900035e4000
RIP: 0010:mmu_spte_clear_track_bits+0x123/0x170
RSP: 0018:ffffc900035e7ab0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 000000010501cc67 RCX: 0000000000000001
RDX: dead0000000000ff RSI: ffff88020e501df8 RDI: 0000000004140700
RBP: ffffc900035e7ad8 R08: 0000000000000100 R09: 0000000000000003
R10: 0000000000000003 R11: 0000000000000005 R12: 000000000010501c
R13: ffffea0004140700 R14: ffff88020e1d0000 R15: 0000000000000000
FS:  00007f0213fbd700(0000) GS:ffff88022fd40000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000022187f000 CR4: 00000000000006e0
Call Trace:
 drop_spte+0x26/0x130
 mmu_page_zap_pte+0xc4/0x160
 kvm_mmu_prepare_zap_page+0x65/0x660
 kvm_mmu_invalidate_zap_all_pages+0xc5/0x1f0
 kvm_mmu_invalidate_zap_pages_in_memslot+0x9/0x10
 kvm_page_track_flush_slot+0x86/0xd0
 kvm_arch_flush_shadow_memslot+0x9/0x10
 __kvm_set_memory_region+0x8fb/0x14f0
 kvm_set_memory_region+0x2f/0x50
 kvm_vm_ioctl+0x559/0xcc0
 ? kvm_vcpu_ioctl+0x171/0x620
 ? __switch_to+0x30b/0x740
 do_vfs_ioctl+0xbb/0x8d0
 ? find_vma+0x23/0x100
 ? __fget_light+0x94/0x110
 SyS_ioctl+0x86/0xa0
 entry_SYSCALL_64_fastpath+0x17/0x98
RIP: 0033:0x7f021c80ddc7
RSP: 002b:00007f0213fbc518 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f021c80ddc7
RDX: 00007f0213fbc5b0 RSI: 000000004020ae46 RDI: 000000000000000a
RBP: 0000000000000000 R08: 00007f020c1698a0 R09: 0000000000000000
R10: 00007f020c1698a0 R11: 0000000000000246 R12: 0000000000000006
R13: 00007f022201c000 R14: 0000000000000002 R15: 0000558c3899e550
Code: ae fc 01 48 85 c0 75 1c 4c 89 e7 e8 98 de fd ff 48 8b 05 81 ae fc 01 48 85 c0 74 ba 48 85 c3 0f 95 c3 eb b8 48 85 c3 74 e7 eb dd <0f> ff eb 97 4c 89 e7 66 0f 1f 44 00 00 e8 6b de fd ff eb 97 31 
---[ end trace 16c196134f0dd0a9 ]---

After this, there are hundreds of repeats and lots of secondary damage which
kills the host quickly.

Usually this happens within a few minutes, but sometimes it takes ~half an
hour to reproduce.  Because of this, it'd be unpleasant to bisect -- is this
problem already known?


Meow!
-- 
âââââââ 
âââââââ Vat kind uf sufficiently advanced technology iz dis!?
âââââââ                                        -- Genghis Ht'rok'din
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