Re: [Qemu-ppc] [PATCH 0/6] spapr: Add optional capabilities

[David Gibson]

On Mon, Dec 18, 2017 at 08:20:18PM +1100, David Gibson wrote:
> This series is a first draft to add the notion of optional
> capabilities to the "pseries" machine type.  A default set of
> capabilities is selected based on the machine type version and
> selected cpu model, but this can be overridden with machine
> parameters.
> 
> The purpose of this is to get rid of a number of places where we
> implicitly decide what features to advertise to the guest based on
> capabilities of the host.  This is bad, because it means it's
> difficult to be certain if machines started at different ends of a
> migration really match from the guest's point of view.
> 
> By giving the user explicit control of these optional features, then
> validating that the chosen ones can be supplied on the host we make
> behaviour more predictable.
> 
> The more specific motivation for this is that POWER9 has bugs in its
> hardware transactional memory (HTM) implementation making it unsafe to
> migrate POWER8 guests to POWER9 if they use HTM.

I've fixed the user-after-free bug Greg pointed out and merged this
into ppc-for-2.12.

-- 
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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