From: christoffer.dall@linaro.org (Christoffer Dall)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] ARM: KVM: drop arbitrary limitation to 4 CPU VMs
Date: Tue, 15 Oct 2013 16:21:08 -0700 [thread overview]
Message-ID: <20131015232108.GD20547@cbox> (raw)
In-Reply-To: <525BAE98.8050505@arm.com>
On Mon, Oct 14, 2013 at 09:43:04AM +0100, Marc Zyngier wrote:
> On 13/10/13 02:09, Christoffer Dall wrote:
> > On Tue, Oct 08, 2013 at 06:17:08PM +0100, Marc Zyngier wrote:
> >> It appears we have an arbitrary limitation where we refuse to
> >> create more than 4 virtual A15 in a single VM.
> >>
> >> This limitation doesn't make much sense (the number 4 probably
> >> comes from the maximum number of CPUs in a A15 cluster, but
> >> KVM doesn't have any notion of cluster), and directly
> >> contradicts CONFIG_MAX_VCPUS.
> >
> > So this comes from the early days where I looked at the A15 TRM and the
> > MPIDR bit field for the CPU ID is limited to 2 bits. Exactly because
> > I wasn't sure what remifications (if any) it would have to start
> > populating this register with cluster id = (vcpu_id / 4) and cpu id =
> > (vcpu_id % 4) I put this nice arbitrary restriction in there.
> >
> > I think we need to fix how we show this register to the guest
> > otherwise... No?
>
> I don't see this being an issue, but if we really want to be 100% true
> to the A15/A7 TRM, we can always compute MPIDR that way, and adjust
> L2CTLR as well.
Even with mach-virt we're still pretending to be an A15/A7 right? I
think we should adhere to that. Is there some other reason why people
shouldn't generally expect MPIDR to be correct (merging this code to KVM
and running in a VM notwithstanding)?
>
> That will require some userspace change in kvmtool though (need to
> change the DT generator to cope with the cluster ID).
>
That would be the less fun part...
-Christoffer
next prev parent reply other threads:[~2013-10-15 23:21 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-08 17:17 [PATCH] ARM: KVM: drop arbitrary limitation to 4 CPU VMs Marc Zyngier
2013-10-09 2:15 ` Peter Maydell
2013-10-09 6:40 ` Marc Zyngier
2013-10-13 1:09 ` Christoffer Dall
2013-10-14 8:43 ` Marc Zyngier
2013-10-15 23:21 ` Christoffer Dall [this message]
2013-10-16 9:49 ` Marc Zyngier
2013-10-16 16:53 ` Christoffer Dall
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