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Re: [Xen-devel] [PATCH v4 0/4] Support for reading runtime hypervisor parameters



On 28.05.19 16:54, Vasilis Liaskovitis wrote:
Currently runtime parameters of the hypervisor cannot be inspected through an
xl command, however they can be changed with the "xl set-parameter" command.
Being able to check these parameters at runtime would be a useful diagnostic
tool.

This patch series implements a new xl command "xl get-parameters"
which takes a string of input parameters and returns their current
values in the hypervisor settings.

Examples:

xl get-parameters "gnttab_max_frames gnttab_max_maptrack_frames"
gnttab_max_frames gnttab_max_maptrack_frames : 64 1024

xl set-parameters gnttab_max_frames=128

xl get-parameters gnttab_max_frames
gnttab_max_frames : 128

xl get-parameters "gnttab_max_frames gnttab_max_maptrack_frames"
gnttab_max_frames gnttab_max_maptrack_frames : 128 1024


Changes v3->v4:

- Fix return value and logging in new libxl function.

Changes v2->v3:

- Several style / formatting fixes
- Limitations for signed integer parameters added in code and commit log.

Changes v1->v2:

- fixed snprintf issues, fixed memory leaks and error handling
- removed unnecessary wrapper function
- OPT_SIZE is handled

Limitations:

- Custom runtime parameters (OPT_CUSTOM) are not supported yet. I'd like
   to do this in a follow-up series. See also discussion at
   https://lists.xenproject.org/archives/html/xen-devel/2019-03/msg01383.html
- For integer parameters (OPT_UINT), only unsigned parameters are printed
   correctly at the moment.

Vasilis Liaskovitis (4):
   xen: add hypercall for getting parameters at runtime
   libxc: add function to get hypervisor parameters
   libxl: add libxl_get_parameters() function
   xl: add new xl command get-parameters

  docs/man/xl.1.pod.in                |   5 ++
  tools/flask/policy/modules/dom0.te  |   2 +-
  tools/libxc/include/xenctrl.h       |   1 +
  tools/libxc/xc_misc.c               |  26 ++++++
  tools/libxl/libxl.c                 |  19 +++++
  tools/libxl/libxl.h                 |   1 +
  tools/xl/xl.h                       |   1 +
  tools/xl/xl_cmdtable.c              |   5 ++
  tools/xl/xl_misc.c                  |  25 ++++++
  xen/common/kernel.c                 | 118 ++++++++++++++++++++++++++++
  xen/common/sysctl.c                 |  52 +++++++++++-
  xen/include/public/sysctl.h         |  18 +++++
  xen/include/xen/lib.h               |   1 +
  xen/xsm/flask/hooks.c               |   3 +
  xen/xsm/flask/policy/access_vectors |   2 +
  15 files changed, 276 insertions(+), 3 deletions(-)


At the Xen developers summit last week in Chicago there was a related
discussion. The basic outcome was that there is some need for a generic
framework to report hypervisor settings to dom0, especially for the
currently active mitigation settings of cpu vulnerabilities. The most
appropriate solution seems to be a hierarchical key-value store in the
hypervisor which can be queried via a new interface. The same interface
would be usable for reading hypervisor parameters, too.


Juergen

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