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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 Jan 2021, at 17:47, Alexander Graf <graf@amazon.com> wrote:
>
> 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
>
Not a particular reason, as we explicitly check for the implementer ID. However,
without CONFIG_ARCH_APPLE, other parts of the support for Apple CPUs
will not be available anyway.
>> +
>> +/*
>> + * 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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