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Re: [Xen-devel] [PATCH RFC] x86: Add hack to disable "Fake HT" mode
- To: Steven Haigh <netwiz@xxxxxxxxx>
- From: George Dunlap <george.dunlap@xxxxxxxxxx>
- Date: Fri, 15 Nov 2019 15:05:11 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Andreas Kinzler <hfp@xxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxx>, Anthony Perard <anthony.perard@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 15 Nov 2019 15:05:22 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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FTR, please avoid top-posting. :-)
On 11/15/19 2:31 PM, Steven Haigh wrote:
> Just regarding the use of a system environment variable to turn this
> feature / bugfix / hack on and off - this would probably break starting
> the VM via the xendomains script.
>
> If the VM definition is in /etc/xen/auto/, then there would be nothing
> to set the environment variable before the VM is launched - hence it
> would not be applied and a guest crash would occur...
>
> Depending on the VM's settings, this would either continue to start &
> crash - or just stop again until it could be started with the ENV variable.
Right. So a couple of options:
1. Users of xendomains could set the environment variable in their
xendomains script
2. We could add a xl.cfg option. Unknown xl.cfg entries are ignored
(for better or for worse); in the future, when the "fake ht" thing is
replaced, we can either continue ignoring it, or give a useful error
message saying how it should be changed.
2a. We could have the config option *replace* the environment variable;
in which case we'd leave libvirt users high and dry
2b. We could have the config option cause xl to *set* the environment
variable, which should continue to allow other toolstacks (even those
not using libxl) to potentially work around the issue.
Right now I'm leaning towards 2b, and having it be in a separate patch.
-George
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