Re: [RFC PATCH 04/13] ppc/spapr: Disable FWNMI capability if KVM does not support it

[Nicholas Piggin]

David Gibson's on March 5, 2020 2:37 pm:
> On Thu, Mar 05, 2020 at 01:51:40PM +1000, Nicholas Piggin wrote:
>> David Gibson's on March 4, 2020 3:57 pm:
>> > On Wed, Mar 04, 2020 at 03:28:41PM +1000, Nicholas Piggin wrote:
>> >> This is a fatal error if KVM does not support this capability, so try to
>> >> disable it if that's the case.
>> > 
>> > Nack.
>> > 
>> > Changing the guest visible environment based on host capabilities
>> > totally breaks the migration model.  If the user has requested an
>> > environment the host can't provide, we have to outright fail instead.
>> 
>> Okay. How are these capabilities requested, do you tend to default on
>> and pass the cap-flag=off parameter?
> 
> I don't entirely understand the question.  The user will use machine
> options of some sort to request the environment they want - plus we
> try to pick a good default for the base machine types.
> 
> The cap-* options are one subset of that, with some inbuilt handling
> (which comes with some restrictions on how they operate).  Above I was
> using "capability" in a broader sense, though.

Yeah okay, I think I answered my own question or fixed my
misunderstanding after going over your comments and reading the
code some more.

Thakns,
Nick