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Date: Wed, 7 Apr 2021 16:51:30 +1000
From: Paul Mackerras <paulus@ozlabs.org>
To: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v6 38/48] KVM: PPC: Book3S HV: Remove support for
 dependent threads mode on P9
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 <20210405011948.675354-39-npiggin@gmail.com>
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On Mon, Apr 05, 2021 at 11:19:38AM +1000, Nicholas Piggin wrote:
> Radix guest support will be removed from the P7/8 path, so disallow
> dependent threads mode on P9.

Dependent threads mode on P9 was added in order to support the mode
where for security reasons you want to restrict the vcpus that run on
a core to all be from the same VM, without requiring all guests to run
single-threaded.  This was (at least at one stage) thought to be a
useful mode for users that are worried about side-channel data leaks.

Now it's possible that that mode is not practically useful for some
reason, or that no-one actually wants it, but its removal should be
discussed.  Also, the fact that we are losing that mode should be
explicit in the commit message.

Paul.