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

From: Peter Maydell
Subject: Re: [Qemu-ppc] [PULL 00/60] ppc-for-4.0 queue 20190310
Date: Tue, 12 Mar 2019 10:01:45 +0000

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.

-- PMM

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