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Re: [Qemu-ppc] [PULL 00/60] ppc-for-4.0 queue 20190310

From: David Gibson
Subject: Re: [Qemu-ppc] [PULL 00/60] ppc-for-4.0 queue 20190310
Date: Tue, 12 Mar 2019 21:33:14 +1100
User-agent: Mutt/1.11.3 (2019-02-01)

On Tue, Mar 12, 2019 at 10:01:45AM +0000, Peter Maydell wrote:
> On Tue, 12 Mar 2019 at 03:34, David Gibson <address@hidden> wrote:
> > Ok, done.  As a rule these warnings are there intentionally for TCG -
> > we want to enable Spectre/Meltdown mitigations by default, but no-one
> > really knows if and how to implement them for TCG.
> For the Arm "block speculation" type instructions what we did was
> say "TCG's execution doesn't speculate in a relevant way, and
> we treat the TCG backends as not a security boundary anyway,
> so we'll end the TB and put in a memory barrier and call that
> sufficient". That is, they're provided for the benefit of
> emulating guest OSes that use them, rather than because they
> make a difference from a security perspective.
> I don't know exactly what the semantics of the PPC mitigations
> are, but we should probably think about and document a coherent
> position on this for TCG.

Yes, but this requires input from someone who understands both Spectre
and TCG well enough, which I am not.

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_!

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