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From: Marc Zyngier <maz@kernel.org>
To: Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc: "Michal Prívozník" <mprivozn@redhat.com>,
	qemu-discuss@nongnu.org, libvirt-users@redhat.com,
	qemu-arm@nongnu.org, kvmarm <kvmarm@lists.cs.columbia.edu>
Subject: Re: Libvirt on little.BIG ARM systems unable to start guest if no cpuset is provided
Date: Tue, 14 Dec 2021 11:00:10 +0000	[thread overview]
Message-ID: <878rwnjvt1.wl-maz@kernel.org> (raw)
In-Reply-To: <242ff064-ba82-a045-a407-eaf9dbe5bb40@gmx.com>

On Tue, 14 Dec 2021 10:21:40 +0000,
Qu Wenruo <quwenruo.btrfs@gmx.com> wrote:
> On 2021/12/14 17:52, Marc Zyngier wrote:
> > The best workaround is to taskset the QEMU process (and I really mean
> > the process, not individual threads) to an homogeneous set of CPUs and
> > be done with it.
> 
> Yeah, that's why the cpuset way is working, as it seems also limiting
> the initial "temporary" VM creating to specified CPUs.
> 
> Just curious, is there some defined common VM related registers that can
> be restore on all cores? (At least for A53 + A72 case).

Most of the registers are common, and most of the feature registers
are actually massaged by KVM to make them look homogeneous if even the
HW isn't. There are however a few registers that need to be exposed to
the guest verbatim, and MIDR_EL1 is the most important one, as it
carries the core 'identity', which an operating system will absolutely
need to implement critical workarounds (and there are no shortage of
them on both A53 and A72).

> If completely no, then virtualization is really not even targeted for
> BIG.little designs I guess.

If your use of virtualisation is to be completely abstracted from the
underlying HW, then you are right, that doesn't really work at all.
Not by design, but because all implementations have embarrassing warts
that need some sort of workarounds.

	M.

-- 
Without deviation from the norm, progress is not possible.
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  reply	other threads:[~2021-12-14 11:00 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <70a2f7d6-5ac1-72df-4a88-b1a662d07070@gmx.com>
     [not found] ` <32bb61a9-0938-d254-0453-18a108bc4b63@redhat.com>
2021-12-13 14:01   ` Libvirt on little.BIG ARM systems unable to start guest if no cpuset is provided Qu Wenruo
2021-12-13 16:06     ` Peter Maydell
2021-12-13 16:49       ` Marc Zyngier
2021-12-14  0:41         ` Qu Wenruo
2021-12-14  0:41           ` Qu Wenruo
2021-12-14  7:53           ` Michal Prívozník
2021-12-14  7:53             ` Michal Prívozník
2021-12-14  8:16             ` Qu Wenruo
2021-12-14  8:16               ` Qu Wenruo
2021-12-14  9:52               ` Marc Zyngier
2021-12-14 10:08                 ` Peter Maydell
2021-12-14 10:33                   ` Marc Zyngier
2021-12-14 10:21                 ` Qu Wenruo
2021-12-14 10:21                   ` Qu Wenruo
2021-12-14 11:00                   ` Marc Zyngier [this message]
2021-12-14  9:34           ` Marc Zyngier
2021-12-14 10:36             ` Daniel P. Berrangé
2021-12-14 10:59               ` Qu Wenruo
2021-12-14 10:59                 ` Qu Wenruo
2021-12-14 11:05                 ` Daniel P. Berrangé
2021-12-14  7:58         ` Michal Prívozník
2021-12-14  7:58           ` Michal Prívozník

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