linux-kernel - Re: [PATCH 1/1] KVM: arm64: Affinity level 3 support

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Date: Tue, 27 Feb 2024 08:10:48 +0000
From: Marc Zyngier <maz@...nel.org>
To: Wei-Lin Chang <r09922117@...e.ntu.edu.tw>
Cc: oliver.upton@...ux.dev,
	james.morse@....com,
	suzuki.poulose@....com,
	yuzenghui@...wei.com,
	catalin.marinas@....com,
	will@...nel.org,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	sauravsc@...zon.com,
	eric.auger@...hat.com
Subject: Re: [PATCH 1/1] KVM: arm64: Affinity level 3 support

On Tue, 27 Feb 2024 02:27:08 +0000,
Wei-Lin Chang <r09922117@...e.ntu.edu.tw> wrote:
> 
> On Sun, 25 Feb 2024 11:19:05 +0000,
> Marc Zyngier <maz@...nel.org> wrote:

[...]

> > I can see multiple problems with this:
> > 
> > - this is the host state, which shouldn't necessarily represent the
> >   guest state. It should be possible to restore a VM that have a
> >   different A3V value and still have the same guarantees.  There is
> >   however a small nit around ICV_CTLR_EL1.A3V, which would require
> >   trapping to emulate the A3V bit.
> > 
> > - this assumes GICv3, which is definitely not universal (we support
> >   GICv2, for which no such restriction actually exists).
> > 
> > Finally, I don't see VM save/restore being addressed here, and I
> > suspect it hasn't been looked at.
> > 
> > Overall, this patch does too many things, and it should be split in
> > discrete changes. I also want to see an actual justification for Aff3
> > support. And if we introduce it, it must be fully virtualised
> > (independent of the A3V support on the host).
> 
> Hi Marc,
> 
> Really appreciate for the feedback. I think I understand most of your
> comments and agree with them. It appears that I don't fully understand
> the changes that I am doing with this. Thanks for explaining.

I hope this doesn't deter you from working on this feature. I'll
happily answer questions and discuss the above points.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.