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From: Christoffer Dall <christoffer.dall@linaro.org>
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>
Subject: Re: [PATCH 5/5] KVM: arm/arm64: allow userspace to set MPIDR
Date: Wed, 8 Mar 2017 09:21:59 -0800	[thread overview]
Message-ID: <20170308172159.GD109908@lvm> (raw)
In-Reply-To: <CAFEAcA_2BtKUnFFciN1v2F3etkDVNvd4+wNOk-DX=hcWDwsCiA@mail.gmail.com>

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

  reply	other threads:[~2017-03-08 17:20 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-27 17:54 [PATCH 0/5] KVM: arm/arm64: fix some races and allow userspace to set MPIDR Andrew Jones
2017-02-27 17:55 ` [PATCH 1/5] KVM: arm/arm64: prepare to use vcpu requests Andrew Jones
2017-03-08 13:21   ` Christoffer Dall
2017-02-27 17:55 ` [PATCH 2/5] KVM: arm/arm64: replace vcpu->arch.pause with a vcpu-request Andrew Jones
2017-03-08 14:33   ` Christoffer Dall
2017-03-08 14:44     ` Andrew Jones
2017-03-13 10:30       ` Christoffer Dall
2017-03-13 17:27         ` Andrew Jones
2017-03-13 18:22           ` Christoffer Dall
2017-02-27 17:55 ` [PATCH 3/5] KVM: arm/arm64: replace vcpu->arch.power_off " Andrew Jones
2017-02-27 17:55 ` [PATCH 4/5] KVM: arm/arm64: fix race in kvm_psci_vcpu_on Andrew Jones
2017-02-27 17:55 ` [PATCH 5/5] KVM: arm/arm64: allow userspace to set MPIDR Andrew Jones
2017-03-08 13:19   ` Christoffer Dall
2017-03-08 14:27     ` Peter Maydell
2017-03-08 17:21       ` Christoffer Dall [this message]
2017-03-08 20:48         ` Peter Maydell
2017-03-08 17:27 ` [PATCH 0/5] KVM: arm/arm64: fix some races and " Christoffer Dall
2017-03-08 17:53   ` Andrew Jones

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