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Re: [PATCH v7 08/12] xen: add /buildinfo/config entry to hypervisor filesystem


On 06.04.20 14:29, Jan Beulich wrote:
On 03.04.2020 17:45, Jürgen Groß wrote:
On 03.04.20 17:33, Jan Beulich wrote:
On 03.04.2020 17:12, Jürgen Groß wrote:
On 03.04.20 16:31, Jan Beulich wrote:
On 02.04.2020 17:46, Juergen Gross wrote:
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -353,6 +353,16 @@ config DOM0_MEM
            Leave empty if you are not sure what to specify.
    +config HYPFS_CONFIG
+    bool "Provide hypervisor .config via hypfs entry"
+    default y

My initial reaction was to ask for "depends on HYPFS", but then
I noticed the earlier patch doesn't introduce such. Am I
mis-remembering that it was agreed to make the whole thing
possible to disable at least in EXPERT mode?

No, I don't remember that agreement.

And TBH I'm not sure this is a good idea, as that would at once make the
plan to replace at least some sysctl and/or domctl interfaces impossible
(like e.g. the last 3 patches of the series are doing already), or at
least would tie the related functionality to CONFIG_HYPFS.

I think that would be fine - that's what config setting are for.
Someone caring about space may not care about runtime setting of

So right now it would start with a plain hypfs available or not.

The next step would be in patch 12 to tell the user he will lose the
capability of setting runtime parameters.

Another planned extension would be to control per-cpupool settings,
which would the go away (possibly functionality being unconditionally
available today).

Next would be the lack of being able to control per-domain mitigations
like XPTI or L1TF, which I'd like to add.

Another thing I wanted to add is some debugging stuff (e.g. to switch
lock profiling using hypfs).

And the list will go on.


Does it really make sense to make a central control and information
interface conditional?

None of the above may be of interest to e.g. embedded use cases.

I'd like at least a second opinion on that topic.

Yes, further opinions would surely help.

Any opinion on making hypfs configurable?

It would be quite some code churn and I want to avoid it in case you
see no benefit in configuring it out for embedded.




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