Re: [Xen-devel] [PATCH] x86/fpu: CR0.TS should be set before trap into PV guest's #NM exception handle

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.11.13 at 01:16, Sarah Newman <srn@xxxxxxxxx> wrote:
> On 11/29/2013 01:42 AM, Jan Beulich wrote:
>> I'm personally not eager to see something like this go in, most
>> importantly because I think bugs should be fixed where they
>> got introduced, not worked around elsewhere, and also
>> because I think that a generally available workaround would
>> lower the chances of the bug getting fixed properly.
> If the proper bug fix was released first would that help?

Perhaps.

>> Apart from that this workaround of yours would have very
>> ugly behavior: If a guest later got updated to a fixed kernel,
>> you'd have to alter its configuration along with booting into
>> the new kernel (i.e. a simple reboot of the VM won't do), or
>> else your new kernel would crash due to not clearing CR0.TS
>> before trying to restore FPU context.
> Assuming it predictably crashed, that would be easier to deal with than 
> occasional silent memory
> corruption.
> 
> I think something could be done with the on_reboot action, maybe a 
> reload-restart?

The thing is that a guest admin may not have access to the VM's
config file, i.e. a satisfactory solution ought to involve only guest
side actions.

Jan


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