linux-kernel - Re: [PATCH v2 1/4] KVM: arm64: Allow userspace to change MIDR

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Message-ID: <87pljh1zgj.wl-maz@kernel.org>
Date: Sun, 16 Feb 2025 19:06:36 +0000
From: Marc Zyngier <maz@...nel.org>
To: luoyonggang@...il.com
Cc: Oliver Upton <oliver.upton@...ux.dev>,
	Sebastian Ott <sebott@...hat.com>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Cornelia Huck <cohuck@...hat.com>,
	Eric Auger <eric.auger@...hat.com>,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] KVM: arm64: Allow userspace to change MIDR_EL1

On Sun, 16 Feb 2025 18:55:23 +0000,
"罗勇刚(Yonggang Luo)" <luoyonggang@...il.com> wrote:
> 
> On Mon, Feb 17, 2025 at 2:09 AM Marc Zyngier <maz@...nel.org> wrote:
> >
> > On Sat, 15 Feb 2025 19:04:20 +0000,
> > "罗勇刚(Yonggang Luo)" <luoyonggang@...il.com> wrote:
> > >
> > > According to this, the MIDR EL1 is updated properly, but the MIDR for
> > > aarch32 is not updated, and I don't know how to hook the update for
> > > MIDR for aarch32
> >
> > It is the same thing. The AArch32 view is configured the same way as
> > the AArch64 view, and there is nothing to do at all (that's what
> > VPIDR_EL2 is all about).
> >
> > With Oliver's change, I'm correctly getting a different MIDR using a
> > hacked up kvmtool, see below. I suspect you're not running with the
> > correct patch applied.
> >
> The applied patch is V2, with writing vpidr_el2 disabled, Is that the cause?
> The branch is here
> https://github.com/lygstate/linux/tree/main
> I am not applying your patch

Well, there is no magic. If you don't write to VPIDR_EL2, not much
will happen. You need to apply Oliver's change instead of the first
patch in this series.

	M.

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