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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20131015232108.GD20547@cbox \
--to=christoffer.dall@linaro.org \
--cc=linux-arm-kernel@lists.infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.