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Date:   Mon, 22 Feb 2021 10:35:25 +0100
From:   Jonathan =?utf-8?Q?Neusch=C3=A4fer?= <j.ne@posteo.net>
To:     Marc Zyngier <maz@kernel.org>
Cc:     linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        linux-kernel@vger.kernel.org,
        Prasad Sodagudi <psodagud@codeaurora.org>,
        Srinivas Ramana <sramana@codeaurora.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Hector Martin <marcan@marcan.st>,
        Ajay Patil <pajay@qti.qualcomm.com>, kernel-team@android.com,
        Will Deacon <will@kernel.org>, Ard Biesheuvel <ardb@kernel.org>
Subject: Re: [PATCH v7 23/23] [DO NOT MERGE] arm64: Cope with CPUs stuck in
 VHE mode
Message-ID: <YDN6BtDhzmF5OtBO@latitude>
References: <20210208095732.3267263-1-maz@kernel.org>
 <20210208095732.3267263-24-maz@kernel.org>
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Hi,

On Mon, Feb 08, 2021 at 09:57:32AM +0000, Marc Zyngier wrote:
> It seems that the CPU known as Apple M1 has the terrible habit
> of being stuck with HCR_EL2.E2H=3D=3D1, in violation of the architecture.

Minor nitpick from the sideline: The M1 SoC has two kinds of CPU in it
(Icestorm and Firestorm), which makes "CPU known as Apple M1" a bit
imprecise.

In practicality it seems unlikely though, that Icestorm and Firestorm
act differently with regards to the code in this patch.


Best regards,
Jonathan Neusch=C3=A4fer

>=20
> Try and work around this deplorable state of affairs by detecting
> the stuck bit early and short-circuit the nVHE dance. It is still
> unknown whether there are many more such nuggets to be found...
>=20
> Reported-by: Hector Martin <marcan@marcan.st>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kernel/head.S     | 33 ++++++++++++++++++++++++++++++---
>  arch/arm64/kernel/hyp-stub.S | 28 ++++++++++++++++++++++++----
>  2 files changed, 54 insertions(+), 7 deletions(-)
[...]

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