Warning from AMD IOMMU performance counters

From	Laura Abbott <labbott@redhat.com>
Newsgroups	linux.kernel
Subject	Warning from AMD IOMMU performance counters
Date	2016-02-19 23:40 +0100
Message-ID	<r41Sq-3SM-27@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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Hi,

Since about 4.4, we've been seeing reports of this warning on every boot
from some users:

WARNING: CPU: 2 PID: 1 at drivers/iommu/amd_iommu_init.c:2301 amd_iommu_pc_get_set_reg_val+0xa8/0xe0()
Modules linked in:
CPU: 2 PID: 1 Comm: swapper/0 Not tainted 4.4.2-300.fc23.x86_64 #1
Hardware name: Hewlett-Packard HP EliteBook 755 G2/221C, BIOS M84 Ver. 01.10 10/20/2015
  0000000000000000 0000000026124b43 ffff88042d687d20 ffffffff813b0c9f
  0000000000000000 ffff88042d687d58 ffffffff810a2f12 ffff88042f014800
  0000000000000040 0000000000000000 ffffffff81d6c73d 0000000000000000
Call Trace:
  [<ffffffff813b0c9f>] dump_stack+0x44/0x55
  [<ffffffff810a2f12>] warn_slowpath_common+0x82/0xc0
  [<ffffffff81d6c73d>] ? memblock_find_dma_reserve+0x16a/0x16a
  [<ffffffff810a305a>] warn_slowpath_null+0x1a/0x20
  [<ffffffff814d3f48>] amd_iommu_pc_get_set_reg_val+0xa8/0xe0
  [<ffffffff81dafda7>] iommu_go_to_state+0x4d6/0x1384
  [<ffffffff813c02ea>] ? kvasprintf+0x7a/0xa0
  [<ffffffff81d6c73d>] ? memblock_find_dma_reserve+0x16a/0x16a
  [<ffffffff81db0cbd>] amd_iommu_init+0x13/0x201
  [<ffffffff81d6c74f>] pci_iommu_init+0x12/0x3c
  [<ffffffff81002123>] do_one_initcall+0xb3/0x200
  [<ffffffff810c0935>] ? parse_args+0x295/0x4b0
  [<ffffffff81d621c8>] kernel_init_freeable+0x189/0x223
  [<ffffffff8178dc00>] ? rest_init+0x80/0x80
  [<ffffffff8178dc0e>] kernel_init+0xe/0xe0
  [<ffffffff81799c8f>] ret_from_fork+0x3f/0x70
  [<ffffffff8178dc00>] ? rest_init+0x80/0x80

Full bugzilla https://bugzilla.redhat.com/show_bug.cgi?id=1310258

Any idea what might be causing this spew?

Thanks,
Laura

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Warning from AMD IOMMU performance counters Laura Abbott <labbott@redhat.com> - 2016-02-19 23:40 +0100
  Re: Warning from AMD IOMMU performance counters Wan Zongshun <vw@iommu.org> - 2016-02-22 03:10 +0100

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