Re: BUG: unable to handle kernel paging request in __kvm_mmu_prepare_zap_page

[Sean Christopherson]

On Mon, Feb 25, 2019 at 06:50:05AM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    94a47529a645 Add linux-next specific files for 20190222
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=13c1c692c00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=51cd1c8c39e8a207
> dashboard link: https://syzkaller.appspot.com/bug?extid=222746e0104bbb617d51
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11fcba7cc00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+222746e0104bbb617d51@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> BUG: unable to handle kernel paging request at ffff88809c0e1000
> #PF error: [PROT] [WRITE] [RSVD]
> PGD b201067 P4D b201067 PUD 21ffff067 PMD 800000009c0001e3
> Oops: 000b [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 7863 Comm: syz-executor.2 Not tainted 5.0.0-rc7-next-20190222
> #41
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:__write_once_size include/linux/compiler.h:224 [inline]
> RIP: 0010:__update_clear_spte_fast arch/x86/kvm/mmu.c:558 [inline]
> RIP: 0010:mmu_spte_clear_no_track arch/x86/kvm/mmu.c:859 [inline]
> RIP: 0010:drop_parent_pte arch/x86/kvm/mmu.c:2051 [inline]
> RIP: 0010:kvm_mmu_unlink_parents arch/x86/kvm/mmu.c:2645 [inline]
> RIP: 0010:__kvm_mmu_prepare_zap_page+0x1ee/0x11a0 arch/x86/kvm/mmu.c:2683
> Code: f8 30 60 00 48 89 de 4c 89 e7 e8 bd ad fe ff 4c 89 e0 48 b9 00 00 00
> 00 00 fc ff df 48 c1 e8 03 80 3c 08 00 0f 85 a5 0d 00 00 <49> c7 04 24 00 00
> 00 00 e8 c5 30 60 00 4c 89 ea 4c 89 fe 48 89 df
> RSP: 0018:ffff88809e96faf0 EFLAGS: 00010246
> RAX: 1ffff1101381c200 RBX: ffff888098149820 RCX: dffffc0000000000
> RDX: 0000000000000000 RSI: ffffffff810ed2f4 RDI: 0000000000000007
> RBP: ffff88809e96fbd0 R08: ffff888094052700 R09: ffffed100e339d92
> R10: ffffed100e339d91 R11: ffff8880719cec8b R12: ffff88809c0e1000
> R13: ffff88809e96fb70 R14: ffffc90006a39000 R15: ffff88809e96fb68
> FS:  000000000239b940(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffff88809c0e1000 CR3: 00000000a143a000 CR4: 00000000001426e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  __kvm_mmu_zap_all+0x1f6/0x350 arch/x86/kvm/mmu.c:5856

This strongly suggests the recent MMU zapping changes[1] are to blame,
but I haven't had any luck reproducing the bug.

Paolo, were you able to make any headway on the kvm-unit-test issues
that are potentially due to the MMU changes?

[1] https://patchwork.kernel.org/cover/10798425/

>  kvm_mmu_zap_all+0x18/0x20 arch/x86/kvm/mmu.c:5870
>  kvm_arch_flush_shadow_all+0x16/0x20 arch/x86/kvm/x86.c:9473
>  kvm_mmu_notifier_release+0x63/0xb0
> arch/x86/kvm/../../../virt/kvm/kvm_main.c:499
>  mmu_notifier_unregister+0x137/0x440 mm/mmu_notifier.c:356
>  kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:745 [inline]
>  kvm_put_kvm+0x553/0xc70 arch/x86/kvm/../../../virt/kvm/kvm_main.c:770
>  kvm_vcpu_release+0x7b/0xa0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2500
>  __fput+0x2e5/0x8d0 fs/file_table.c:278
>  ____fput+0x16/0x20 fs/file_table.c:309
>  task_work_run+0x14a/0x1c0 kernel/task_work.c:113
>  tracehook_notify_resume include/linux/tracehook.h:188 [inline]
>  exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:166
>  prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
>  syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
>  do_syscall_64+0x52d/0x610 arch/x86/entry/common.c:293
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x411d31
> Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 94 19 00 00 c3 48
> 83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 89
> c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
> RSP: 002b:00007ffe9da10de0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
> RAX: 0000000000000000 RBX: 0000000000000006 RCX: 0000000000411d31
> RDX: 0000000000000000 RSI: 0000000000740528 RDI: 0000000000000005
> RBP: 0000000000000000 R08: 0000000000740520 R09: 000000000000dec8
> R10: 00007ffe9da10d00 R11: 0000000000000293 R12: 0000000000000000
> R13: 0000000000000001 R14: 0000000000000007 R15: 0000000000000002
> Modules linked in:
> CR2: ffff88809c0e1000
> ---[ end trace 4b53a3c1b491aa63 ]---
> RIP: 0010:__write_once_size include/linux/compiler.h:224 [inline]
> RIP: 0010:__update_clear_spte_fast arch/x86/kvm/mmu.c:558 [inline]
> RIP: 0010:mmu_spte_clear_no_track arch/x86/kvm/mmu.c:859 [inline]
> RIP: 0010:drop_parent_pte arch/x86/kvm/mmu.c:2051 [inline]
> RIP: 0010:kvm_mmu_unlink_parents arch/x86/kvm/mmu.c:2645 [inline]
> RIP: 0010:__kvm_mmu_prepare_zap_page+0x1ee/0x11a0 arch/x86/kvm/mmu.c:2683
> Code: f8 30 60 00 48 89 de 4c 89 e7 e8 bd ad fe ff 4c 89 e0 48 b9 00 00 00
> 00 00 fc ff df 48 c1 e8 03 80 3c 08 00 0f 85 a5 0d 00 00 <49> c7 04 24 00 00
> 00 00 e8 c5 30 60 00 4c 89 ea 4c 89 fe 48 89 df
> RSP: 0018:ffff88809e96faf0 EFLAGS: 00010246
> RAX: 1ffff1101381c200 RBX: ffff888098149820 RCX: dffffc0000000000
> RDX: 0000000000000000 RSI: ffffffff810ed2f4 RDI: 0000000000000007
> RBP: ffff88809e96fbd0 R08: ffff888094052700 R09: ffffed100e339d92
> R10: ffffed100e339d91 R11: ffff8880719cec8b R12: ffff88809c0e1000
> R13: ffff88809e96fb70 R14: ffffc90006a39000 R15: ffff88809e96fb68
> FS:  000000000239b940(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffff88809c0e1000 CR3: 00000000a143a000 CR4: 00000000001426e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 
> 
> ---
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