Re: [Xen-devel] [PATCH RFC] x86: Add hack to disable "Fake HT" mode

[Jan Beulich <jbeulich@xxxxxxxx>]

On 15.11.2019 16:05, George Dunlap wrote:
> 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.

And how would any of these allow to deal with heterogeneous sets of
guests?

Jan

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