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

[David Gibson]

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.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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