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From: Arnd Bergmann <arnd@kernel.org>
To: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Marc Zyngier <maz@kernel.org>, Hector Martin <marcan@marcan.st>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Mohamed Mediouni <mohamed.mediouni@caramail.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Stan Skowronek <stan@corellium.com>
Subject: Re: [RFC PATCH 3/7] arm64: mm: use nGnRnE instead of nGnRE on Apple processors
Date: Thu, 21 Jan 2021 12:38:44 +0100
Message-ID: <CAK8P3a0mp93afoWHnYiJ0B4uGQCG4q4W4A-O0+Cj8nCd6nL8dg@mail.gmail.com> (raw)
In-Reply-To: <20210121112725.GA21750@willie-the-truck>

On Thu, Jan 21, 2021 at 12:32 PM Will Deacon <will@kernel.org> wrote:
> On Wed, Jan 20, 2021 at 02:27:13PM +0100, Mohamed Mediouni wrote:
> > Use nGnRnE instead of nGnRE on Apple SoCs to workaround a serious hardware quirk.
> >  /*
> >   * Default MAIR_EL1. MT_NORMAL_TAGGED is initially mapped as Normal memory and
> >   * changed during __cpu_setup to Normal Tagged if the system supports MTE.
> > @@ -432,6 +451,13 @@ SYM_FUNC_START(__cpu_setup)
> >        * Memory region attributes
> >        */
> >       mov_q   x5, MAIR_EL1_SET
> > +#ifdef CONFIG_ARCH_APPLE
> > +     mrs     x0, MIDR_EL1
> > +     lsr     w0, w0, #24
> > +     mov_q   x1, MAIR_EL1_SET_APPLE
> > +     cmp     x0, #0x61                       // 0x61 = Implementer: Apple
> > +     csel    x5, x1, x5, eq
>
> Why does this need to be done so early? It would be a lot cleaner if we
> could detect this in a similar fashion to other errata and update the MAIR
> appropriately. If that's not possible because of early IO mappings (which
> ones?), then we could instead initialise to nGnRnE unconditionally, but
> relax it to nGnRE if we detect that we _don't_ have the erratum.

There is (at least) the custom SMP startup code that uses device
mappings. If that's the only thing that needs the modified MAIR
to be used early, I'd consider that one more reason against doing the
custom cpu_operations for now.

       Arnd

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Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-20 13:27 [RFC PATCH 0/7] Linux on Apple Silicon Mohamed Mediouni
2021-01-20 13:27 ` [RFC PATCH 1/7] arm64: kernel: FIQ support Mohamed Mediouni
2021-01-20 13:27 ` [RFC PATCH 2/7] arm64: kernel: Add a WFI hook Mohamed Mediouni
2021-01-20 16:46   ` Alexander Graf
     [not found]     ` <94C20F55-D3B8-4349-B26F-9EA8AAEBF639@caramail.com>
2021-01-21 12:33       ` Hector Martin 'marcan'
2021-01-21 10:52   ` Arnd Bergmann
2021-01-21 11:01     ` Mohamed Mediouni
2021-01-21 11:36       ` Arnd Bergmann
2021-01-20 13:27 ` [RFC PATCH 3/7] arm64: mm: use nGnRnE instead of nGnRE on Apple processors Mohamed Mediouni
2021-01-20 16:47   ` Alexander Graf
2021-01-20 18:06     ` Mohamed Mediouni
2021-01-20 18:10       ` Alexander Graf
2021-01-21 11:27   ` Will Deacon
2021-01-21 11:38     ` Arnd Bergmann [this message]
2021-01-21 11:44     ` Marc Zyngier
2021-01-21 12:47       ` Will Deacon
2021-01-21 15:12         ` Mohamed Mediouni
2021-01-21 16:25           ` Marc Zyngier
2021-01-21 17:55             ` Will Deacon
2021-01-21 18:15               ` Marc Zyngier
2021-01-21 18:22                 ` Mohamed Mediouni
2021-01-21 18:22                 ` Will Deacon
2021-01-20 13:27 ` [RFC PATCH 4/7] irqchip/apple-aic: Add support for Apple AIC Mohamed Mediouni
2021-01-20 17:11   ` Alexander Graf
2021-01-20 18:04     ` Mohamed Mediouni
2021-01-20 20:16       ` Andrew Lunn
2021-01-20 21:18   ` Stan Skowronek
2021-01-21  9:48   ` Linus Walleij
2021-01-21 10:37     ` Arnd Bergmann
2021-01-21 15:29       ` Hector Martin 'marcan'
2021-01-21 17:09         ` Rob Herring
2021-01-21 17:45       ` Rob Herring
2021-01-21 16:44     ` Rob Herring
2021-01-21 16:53   ` Hector Martin 'marcan'
2021-01-20 13:27 ` [RFC PATCH 5/7] arm64/Kconfig: Add Apple Silicon SoC platform Mohamed Mediouni
2021-01-20 13:27 ` [RFC PATCH 6/7] arm64: kernel: Apple CPU start driver Mohamed Mediouni
2021-01-21 11:14   ` Arnd Bergmann
2021-01-20 13:27 ` [RFC PATCH 7/7] irqchip/apple-aic: add SMP support to the Apple AIC driver Mohamed Mediouni
2021-01-21 12:44   ` Arnd Bergmann
2021-01-21 12:50     ` Mohamed Mediouni
2021-01-21 13:00       ` Arnd Bergmann
2021-01-21 13:01         ` Hector Martin 'marcan'
2021-01-21 13:22       ` Marc Zyngier
2021-01-21 13:32         ` Mark Rutland
2021-01-21 14:05           ` Marc Zyngier
2021-01-21 13:34         ` Mohamed Mediouni
2021-01-21 14:10           ` Marc Zyngier
2021-01-21 15:09             ` Arnd Bergmann
2021-01-21 15:18               ` Mohamed Mediouni
2021-01-21 16:40       ` Rob Herring
2021-01-21 16:43         ` Mohamed Mediouni
2021-01-21 17:37           ` Rob Herring
2021-01-21 18:08             ` Mohamed Mediouni
2021-01-21 18:57               ` Rob Herring
2021-02-02 19:15   ` Linus Walleij

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