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SubjectRe: [RFC PATCH 3/7] arm64: mm: use nGnRnE instead of nGnRE on Apple processors
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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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