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From: Alexander Graf <graf@amazon.com>
To: Mohamed Mediouni <mohamed.mediouni@caramail.com>,
	<linux-arm-kernel@lists.infradead.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Hector Martin <marcan@marcan.st>,
	linux-kernel@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
	Will Deacon <will@kernel.org>,
	Stan Skowronek <stan@corellium.com>
Subject: Re: [RFC PATCH 3/7] arm64: mm: use nGnRnE instead of nGnRE on Apple processors
Date: Wed, 20 Jan 2021 17:47:33 +0100
Message-ID: <ce5692a9-e716-514a-f196-b0645bb03eb8@amazon.com> (raw)
In-Reply-To: <20210120132717.395873-4-mohamed.mediouni@caramail.com>

On 20.01.21 14:27, Mohamed Mediouni wrote:
> Use nGnRnE instead of nGnRE on Apple SoCs to workaround a serious hardware quirk.
> 
> On Apple processors, writes using the nGnRE device memory type get dropped in flight,
> getting to nowhere.
> 
> Signed-off-by: Stan Skowronek <stan@corellium.com>
> Signed-off-by: Mohamed Mediouni <mohamed.mediouni@caramail.com>
> ---
>   arch/arm64/mm/proc.S | 26 ++++++++++++++++++++++++++
>   1 file changed, 26 insertions(+)
> 
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index 1f7ee8c8b7b8..06436916f137 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -51,6 +51,25 @@
>   #define TCR_KASAN_HW_FLAGS 0
>   #endif
> 
> +#ifdef CONFIG_ARCH_APPLE

Is there any particular reason for this #ifdef?


Alex

> +
> +/*
> + * Apple cores appear to black-hole writes done with nGnRE.
> + * We settled on a work-around that uses MAIR vs changing every single user of
> + * nGnRE across the arm64 code.
> + */
> +
> +#define MAIR_EL1_SET_APPLE						\
> +	(MAIR_ATTRIDX(MAIR_ATTR_DEVICE_nGnRnE, MT_DEVICE_nGnRnE) |	\
> +	 MAIR_ATTRIDX(MAIR_ATTR_DEVICE_nGnRnE, MT_DEVICE_nGnRE) |	\
> +	 MAIR_ATTRIDX(MAIR_ATTR_DEVICE_GRE, MT_DEVICE_GRE) |		\
> +	 MAIR_ATTRIDX(MAIR_ATTR_NORMAL_NC, MT_NORMAL_NC) |		\
> +	 MAIR_ATTRIDX(MAIR_ATTR_NORMAL, MT_NORMAL) |			\
> +	 MAIR_ATTRIDX(MAIR_ATTR_NORMAL_WT, MT_NORMAL_WT) |		\
> +	 MAIR_ATTRIDX(MAIR_ATTR_NORMAL, MT_NORMAL_TAGGED))
> +
> +#endif
> +
>   /*
>    * 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
> +#endif
>   #ifdef CONFIG_ARM64_MTE
>   	mte_tcr	.req	x20
> 
> --
> 2.29.2
> 




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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 [this message]
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
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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