Re: [PATCH 3/3] domctl: pause vCPU for context reads

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 05/02/14 15:39, Jan Beulich wrote:
>>>> On 05.02.14 at 16:29, Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>> On 05/02/14 14:54, Jan Beulich wrote:
>>> "Base" context reads already paused the subject vCPU when being the
>>> current one, but that special case isn't being properly dealt with
>>> anyway (at the very least when x86's fsgsbase feature is in use), so
>>> just disallow it.
>>>
>>> "Extended" context reads so far didn't do any pausing.
>>>
>>> While we can't avoid the reported data being stale by the time it
>>> arrives at the caller, this way we at least guarantee that it is
>>> consistent.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> Now I come to think about it, is this an ABI change, as we are now
>> disallowing a control domain to issue these hypercalls on itself?
> Of course it is, and intentionally so. As was patch 2. And imo it
> was never correct to allow this.
>
> Jan
>

It is certainly possible to get libxc to do this, but I would agree that
it has no valid use.

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>