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Date: Mon, 21 Aug 2017 21:12:03 +0200
From: Adam Borowski <kilobyte@angband.pl>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        kvm <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: kvm splat in mmu_spte_clear_track_bits
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On Mon, Aug 21, 2017 at 09:26:57AM +0800, Wanpeng Li wrote:
> 2017-08-21 7:13 GMT+08:00 Adam Borowski <kilobyte@angband.pl>:
> > Hi!
> > I'm afraid I keep getting a quite reliable, but random, splat when running
> > KVM:
> 
> I reported something similar before. https://lkml.org/lkml/2017/6/29/64

Your problem seems to require OOM; I don't have any memory pressure at all:
running a single 2GB guest while there's nothing big on the host (bloatfox,
xfce, xorg, terminals + some minor junk); 8GB + (untouched) swap.  There's
no memory pressure inside the guest either -- none was Linux (I wanted to
test something on hurd, kfreebsd) and I doubt they even got to use all of
their frames.

Also, it doesn't reproduce for me on 4.12.

> > ------------[ 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?

-- 
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