From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoffer Dall <christoffer.dall@linaro.org>
Subject: Re: [PATCH 5/5] KVM: arm/arm64: allow userspace to set MPIDR
Date: Wed, 8 Mar 2017 09:21:59 -0800
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>, Ashok Kumar <ashoks@broadcom.com>, Igor Mammedov <imammedo@redhat.com>, "kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>
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On Wed, Mar 08, 2017 at 03:27:28PM +0100, Peter Maydell wrote:
> On 8 March 2017 at 14:19, Christoffer Dall <christoffer.dall@linaro.org> wrote:
> > Isn't this all super racy?  What prevents two VCPUs from getting the
> > same MPIDR at the same time?
> 
> From a userspace API point of view, I was expecting this to be
> "just don't do that then" territory, ie it's userspace's job
> to set the MPIDRs to something that makes sense. Does KVM
> actually care internally what the MPIDR presented to the guest is?
> (In theory I don't see why you shouldn't be able to present
> the guest with a bit of bogus hardware that claims the same
> MPIDR for all cores.)
> 

I think it's important that we maintain a strict mapping between an
MPIDR and a VCPU at any given time, because otherwise, we'll have
problems knowing which redestributor belongs to which VCPU and making
other qualified decisions in the KVM/ARM implementation.

Thanks,
-Christoffer