Re: [Xen-devel] Status of 4.13

[George Dunlap <George.Dunlap@xxxxxxxxxx>]

> On Nov 21, 2019, at 8:41 AM, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> 
> On 21.11.2019 08:36, Jürgen Groß wrote:
>> On 21.11.19 08:30, Steven Haigh wrote:
>>> On 2019-11-21 17:05, Jürgen Groß wrote:
>>>> Where do we stand with Xen 4.13 regarding blockers and related patches?
>>>> 
>>>> 2. Ryzen/Rome failures with Windows guests:
>>>>    What is the currently planned way to address the problem? Who is
>>>>    working on that?
>>> 
>>> A workaround was found by specifying cpuid values in the Windows VM 
>>> config file.
>>> 
>>> The workaround line is:
>>> cpuid = [ "0x80000008:ecx=xxxxxxxxxxxxxxxx0100xxxxxxxxxxxx" ]
>>> 
>>> It was suggested that this be documented - but no immediate action 
>>> should be taken - with a view to correct this properly in 4.14.
>> 
>> I'm aware of the suggestion, but not of any decision. :-)
> 
> It was my understanding that we'd cap the 4-bit value to 7 for
> the time being. I think George was planning to send a patch.

On that also, I’m aware of the suggestion, but not of any decision.  I don’t 
think I got much feedback, positive or negative, about the idea.

Suppose we implement the limit for 4.13. If someone runs Linux VMs on 4.12 a 
system with a hardware value of 7 for apic_id_size, the guests will see 8.  If 
they then migrate to 4.13, the value will magically change under their feet to 
7.  Is that OK?

 -George
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