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Bug#871608: linux-image-4.9.0-3-amd64: Linux kernel should handle decreasing cpu steal clock counter gracefully

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Package: src:linux
Version: 4.9.30-2+deb9u3
Severity: normal
Tags: patch

Dear Maintainer,

running Debian Stretch as a paravirtualized guest under Xen, the kernel
obtains its cpu steal time counter from the virtualization host. On some
hosts, occasionally a slight decrease in the cpu steal time is returned
which leads to an overflow of unsigned variables in the kernel and
subsequent errors in steal time accounting (such as backwards running
counters). This renders tools like "top" or "vmstat" broken in a way
that the cpu utilization cannot be determined anymore.

While this is likely a bug in the virtualization environment, the kernel
running as a guest should deal with this gracefully. I attached a patch
to this report which fixes the errors caused by this on the guest.
Kernel versions 4.7 and older, as well as 4.11 and newer should not be
affected by this issue.

Bug #785557 shows that behavior like this is caused by some broken KVM
hosts. I myself experience this on a Xen host which unfortunately I have
no more information about.

A more detailled description of the issue is part of the patch header,
as well as the following blog post:
https://0xstubs.org/debugging-a-flaky-cpu-steal-time-counter-on-a-paravirtualized-xen-guest/

I would appreciate inclusion of this patch in Debian as this issue may
affect other people running on buggy virtualization hosts and the patch
should not influence other systems.

Note that the system I report this from already runs a customly patched
kernel which may influence some of the information below.

-- Package-specific info:
** Version:
Linux version 4.9.0-3-amd64 (debian-kernel@lists.debian.org) (gcc version 6.3.0 20170516 (Debian 6.3.0-18) ) #1 SMP Debian 4.9.30-2+deb9u3+lass1 (2017-08-08)

** Command line:
root=/dev/xvda ro 

** Not tainted

** Kernel log:
Unable to read kernel log; any relevant messages should be attached

** Model information

** Loaded modules:
ipt_REJECT
nf_reject_ipv4
binfmt_misc
xt_multiport
iptable_filter
intel_rapl
sb_edac
edac_core
evdev
kvm_intel
kvm
irqbypass
crct10dif_pclmul
crc32_pclmul
ghash_clmulni_intel
pcspkr
intel_rapl_perf
ip_tables
x_tables
autofs4
ext4
crc16
jbd2
fscrypto
ecb
mbcache
btrfs
crc32c_generic
xor
raid6_pq
crc32c_intel
xen_netfront
xen_blkfront
aesni_intel
aes_x86_64
glue_helper
lrw
gf128mul
ablk_helper
cryptd

** PCI devices:
not available

** USB devices:
not available


-- System Information:
Debian Release: 9.1
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.9.0-3-amd64 (SMP w/1 CPU core)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages linux-image-4.9.0-3-amd64 depends on:
ii  initramfs-tools [linux-initramfs-tool]  0.130
ii  kmod                                    23-2
ii  linux-base                              4.5

Versions of packages linux-image-4.9.0-3-amd64 recommends:
ii  firmware-linux-free  3.4
ii  irqbalance           1.1.0-2.3

Versions of packages linux-image-4.9.0-3-amd64 suggests:
pn  debian-kernel-handbook               <none>
pn  grub-pc | grub-efi-amd64 | extlinux  <none>
pn  linux-doc-4.9                        <none>

Versions of packages linux-image-4.9.0-3-amd64 is related to:
pn  firmware-amd-graphics     <none>
pn  firmware-atheros          <none>
pn  firmware-bnx2             <none>
pn  firmware-bnx2x            <none>
pn  firmware-brcm80211        <none>
pn  firmware-cavium           <none>
pn  firmware-intel-sound      <none>
pn  firmware-intelwimax       <none>
pn  firmware-ipw2x00          <none>
pn  firmware-ivtv             <none>
pn  firmware-iwlwifi          <none>
pn  firmware-libertas         <none>
pn  firmware-linux-nonfree    <none>
pn  firmware-misc-nonfree     <none>
pn  firmware-myricom          <none>
pn  firmware-netxen           <none>
pn  firmware-qlogic           <none>
pn  firmware-realtek          <none>
pn  firmware-samsung          <none>
pn  firmware-siano            <none>
pn  firmware-ti-connectivity  <none>
pn  xen-hypervisor            <none>

-- no debconf information

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Bug#871608: linux-image-4.9.0-3-amd64: Linux kernel should handle decreasing cpu steal clock counter gracefully Michael Lass <bevan@bi-co.net> - 2017-08-09 23:10 +0200
  Processed: Re: Bug#871608: linux-image-4.9.0-3-amd64: Linux  kernel should handle decreasing cpu steal clock counter gracefully owner@bugs.debian.org (Debian Bug Tracking System) - 2017-09-25 02:10 +0200
  Bug#871608: linux-image-4.9.0-3-amd64: Linux kernel should handle decreasing cpu steal clock counter gracefully Ben Hutchings <ben@decadent.org.uk> - 2017-09-25 02:10 +0200
    Bug#871608: linux-image-4.9.0-3-amd64: Linux kernel should handle decreasing cpu steal clock counter gracefully Michael Laß <bevan@bi-co.net> - 2017-09-25 09:40 +0200
    Bug#871608: linux-image-4.9.0-3-amd64: Linux kernel should handle decreasing cpu steal clock counter gracefully Michael Laß <bevan@bi-co.net> - 2017-10-13 00:40 +0200
  Bug#871608: linux-image-4.9.0-3-amd64: Linux kernel should handle decreasing cpu steal clock counter gracefully Hans van Kranenburg <hans.van.kranenburg@mendix.com> - 2017-11-15 14:40 +0100
  Bug#871608: linux-image-4.9.0-3-amd64: Linux kernel should handle decreasing cpu steal clock counter gracefully Hans van Kranenburg <hans.van.kranenburg@mendix.com> - 2017-12-01 17:40 +0100

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