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

From: Juergen Gross <jgross@suse.com>
To: Vasilis Liaskovitis <vliaskovitis@suse.com>,
	xen-devel@lists.xenproject.org
Cc: sstabellini@kernel.org, wei.liu2@citrix.com,
	George.Dunlap@eu.citrix.com, andrew.cooper3@citrix.com,
	ian.jackson@eu.citrix.com, tim@xen.org, jbeulich@suse.com,
	anthony.perard@citrix.com, dgdegra@tycho.nsa.gov
Subject: Re: [Xen-devel] [PATCH v4 0/4] Support for reading runtime hypervisor parameters
Date: Mon, 15 Jul 2019 06:27:31 +0200	[thread overview]
Message-ID: <453c213e-48e3-25bf-b9fd-e3e5dafbcb0d@suse.com> (raw)
In-Reply-To: <20190528145416.16918-1-vliaskovitis@suse.com>

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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