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[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

Darn, I was chasing my own stupidity. Seems that when I added the memory
limit I got the syntax wrong (which seems to cause less issues for 64bit
than it does for 32bit). I was using "dom0_mem=xM:max=xM" which is
wrong. The correct syntax is "dom0_mem=xM,max:xM". The result of the bad
syntax most likely is that dom0 gets xM of memory active but the full
memory as possible spare.

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https://bugs.launchpad.net/bugs/1576564

Title:
  Xen 32bit dom0 on 64bit hypervisor: bad page flags

Status in linux package in Ubuntu:
  Triaged
Status in xen package in Ubuntu:
  Triaged

Bug description:
  This problem is a mix between running certain versions of 32bit Linux
  kernel dom0 on certain versions of 64bit Xen hypervisor, combined with
  certain memory clamping settings.

  Xen 4.4.2 + Linux 3.13.x
   -> at least boots without messages
  Xen 4.5.0 + linux 3.19.x
   -> at least boots without messages
  Xen 4.5.1 + Linux 4.2.x
   * dom0_mem 512M, 4096M, or unlimited
     -> boot without messages
   * dom0_mem between 1024M and 3072M (inclusive)
     -> bad page messages (but finishes boot)
  Xen 4.6 + Linux 4.2.x
   -> all cases as with Xen 4.5.1
  Xen 4.6 + Linux 4.4.x..4.6-rc5
   The boot for 512M,4096M, and unlimited looks good as well. Though trying to
   start a domU without dom0_mem set caused a crash when ballooning (but I
   think this should be a seperate bug)
   Using a dom0_mem range between 1G and 3G it looks like still producing the
   bad page flags bug message and additionally panicking + reboot.
   Unfortunately there is no clear panic message, the serial console
   seems to be overwhelmed.

  The bad page bug generally looks like this (the pfn numbers seem to be
  towards the end of the allocated range.

  [    8.980150] BUG: Bad page state in process swapper/0  pfn:7fc22
  [    8.980238] page:f4566550 count:0 mapcount:0 mapping:  (null) index:0x0
  [    8.980328] flags: 0x7000400(reserved)
  [    8.980486] page dumped because: PAGE_FLAGS_CHECK_AT_PREP flag set
  [    8.980575] bad because of flags:
  [    8.980688] flags: 0x400(reserved)
  [    8.980844] Modules linked in:
  [    8.980960] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G    B           4.2.0-19-
  generic #23-Ubuntu
  [    8.981084] Hardware name: Supermicro H8SGL/H8SGL, BIOS 3.0        08/31/2012
  [    8.981177]  c1a649a7 23e07668 00000000 e9cafce4 c175e501 f4566550 e9cafd08 c
  1166897
  [    8.981608]  c19750a4 e9d183ec 0007fc22 007fffff c1975630 c1978e86 00000001 e
  9cafd74
  [    8.982074]  c1169f83 00000002 00000141 0004a872 c1af3644 00000000 ee44bce4 e
  e44bce4
  [    8.982506] Call Trace:
  [    8.982582]  [<c175e501>] dump_stack+0x41/0x52
  [    8.982666]  [<c1166897>] bad_page+0xb7/0x110
  [    8.982749]  [<c1169f83>] get_page_from_freelist+0x2d3/0x610
  [    8.982838]  [<c116a4f3>] __alloc_pages_nodemask+0x153/0x910
  [    8.982926]  [<c122ee62>] ? find_entry.isra.13+0x52/0x90
  [    8.983013]  [<c11b0f75>] ? kmem_cache_alloc_trace+0x175/0x1e0
  [    8.983102]  [<c10b1c96>] ? __raw_callee_save___pv_queued_spin_unlock+0x6/0x10
  [    8.983223]  [<c11b0ddd>] ? __kmalloc+0x21d/0x240
  [    8.983308]  [<c119cc2e>] __vmalloc_node_range+0x10e/0x210
  [    8.983433]  [<c1148fa7>] ? bpf_prog_alloc+0x37/0xa0
  [    8.983518]  [<c119cd96>] __vmalloc_node+0x66/0x70
  [    8.983604]  [<c1148fa7>] ? bpf_prog_alloc+0x37/0xa0
  [    8.983689]  [<c119cdd4>] __vmalloc+0x34/0x40
  [    8.983773]  [<c1148fa7>] ? bpf_prog_alloc+0x37/0xa0
  [    8.983859]  [<c1148fa7>] bpf_prog_alloc+0x37/0xa0
  [    8.983944]  [<c167cc8c>] bpf_prog_create+0x2c/0x90
  [    8.984034]  [<c1b6741e>] ? bsp_pm_check_init+0x11/0x11
  [    8.984121]  [<c1b68401>] ptp_classifier_init+0x2b/0x44
  [    8.984207]  [<c1b6749a>] sock_init+0x7c/0x83
  [    8.984291]  [<c100211a>] do_one_initcall+0xaa/0x200
  [    8.984376]  [<c1b6741e>] ? bsp_pm_check_init+0x11/0x11
  [    8.984463]  [<c1b1654c>] ? repair_env_string+0x12/0x54
  [    8.984551]  [<c1b16cf6>] ? kernel_init_freeable+0x126/0x1d9
  [    8.984726]  [<c1755fb0>] kernel_init+0x10/0xe0
  [    8.984846]  [<c10929b1>] ? schedule_tail+0x11/0x50
  [    8.984932]  [<c1764141>] ret_from_kernel_thread+0x21/0x30
  [    8.985019]  [<c1755fa0>] ? rest_init+0x70/0x70

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