Re: [PATCH] x86: Control CR0 TS behavior using dev_na_ts_allowed

[George Dunlap <george.dunlap@eu.citrix.com>]

On 03/17/2014 01:35 PM, Jan Beulich wrote:
>>>> On 17.03.14 at 13:42, George Dunlap <George.Dunlap@eu.citrix.com> wrote:
>> On Mon, Mar 17, 2014 at 8:38 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>>> On 17.03.14 at 04:30, Sarah Newman <srn@prgmr.com> wrote:
>>> Not being convinced at all that this is the right approach (in
>>> particular it remains unclear how an affected guest should deal with
>>> running on a hypervisor not supporting the new interface)
>> It looks like the intention of this patch was that if the dom0
>> administrator enables the new option, then it will be on by default,
>> *but* the guest can disable the new behavior.  That way, if an admin
>> knows that she's running all PVOPS kernels (no "classic Xen" kernels),
>> she can enable it system-wide.  Older PVOPS kernels will behave
>> correctly (but a bit slowly), and newer PVOPS kernels will switch to
>> the PVABI behavior and reap the performance benefit.
>>
>> Newer PVOPS kernels running on older hypervisors will simply use the
>> PVABI behavior.
> But if that works correctly, then there's no hypervisor/tools
> change needed in the first place.

Yes, there's still a need to run *old* PVOPS kernels on *new* 
hypervisors.  That (as I understand it) is the point of this patch.

  -George