linux-kernel - Re: [PATCH v2 1/7] arm64: add CPU field to struct thread

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Date:   Thu, 30 Sep 2021 15:23:10 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Keith Packard <keithpac@...zon.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v2 1/7] arm64: add CPU field to struct thread_info



Le 30/09/2021 à 15:20, Ard Biesheuvel a écrit :
> On Thu, 30 Sept 2021 at 15:15, Christophe Leroy
> <christophe.leroy@...roup.eu> wrote:
>>
>>
>>
>> Le 30/09/2021 à 15:07, Ard Biesheuvel a écrit :
>>> On Thu, 30 Sept 2021 at 15:06, Christophe Leroy
>>> <christophe.leroy@...roup.eu> wrote:
>>>>
>>>>
>>>>
>>>> Le 30/09/2021 à 14:58, Ard Biesheuvel a écrit :
>>>>> The CPU field will be moved back into thread_info even when
>>>>> THREAD_INFO_IN_TASK is enabled, so add it back to arm64's definition of
>>>>> struct thread_info.
>>>>>
>>>>> Note that arm64 always has CONFIG_SMP=y so there is no point in guarding
>>>>> the CPU field with an #ifdef.
>>>>>
>>>>> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
>>>>> Acked-by: Catalin Marinas <catalin.marinas@....com>
>>>>> Acked-by: Mark Rutland <mark.rutland@....com>
>>>>> ---
>>>>>     arch/arm64/include/asm/thread_info.h | 1 +
>>>>>     arch/arm64/kernel/asm-offsets.c      | 1 +
>>>>>     2 files changed, 2 insertions(+)
>>>>>
>>>>> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
>>>>> index 6623c99f0984..c02bc8c183c3 100644
>>>>> --- a/arch/arm64/include/asm/thread_info.h
>>>>> +++ b/arch/arm64/include/asm/thread_info.h
>>>>> @@ -42,6 +42,7 @@ struct thread_info {
>>>>>         void                    *scs_base;
>>>>>         void                    *scs_sp;
>>>>>     #endif
>>>>> +     u32                     cpu;
>>>>>     };
>>>>>
>>>>>     #define thread_saved_pc(tsk)        \
>>>>> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
>>>>> index 551427ae8cc5..cee9f3e9f906 100644
>>>>> --- a/arch/arm64/kernel/asm-offsets.c
>>>>> +++ b/arch/arm64/kernel/asm-offsets.c
>>>>> @@ -29,6 +29,7 @@ int main(void)
>>>>>       DEFINE(TSK_ACTIVE_MM,             offsetof(struct task_struct, active_mm));
>>>>>       DEFINE(TSK_CPU,           offsetof(struct task_struct, cpu));
>>>>>       BLANK();
>>>>> +  DEFINE(TSK_TI_CPU,         offsetof(struct task_struct, thread_info.cpu));
>>>>
>>>> Why adding that now ? For powerpc you do the switch in 5.
>>>>
>>>
>>>
>>> Why not?
>>
>> Maybe to remain consistent between archs ?
>>
> 
> Does it matter?

Probably not :)

> 
>>>
>>>
>>>>>       DEFINE(TSK_TI_FLAGS,              offsetof(struct task_struct, thread_info.flags));
>>>>>       DEFINE(TSK_TI_PREEMPT,    offsetof(struct task_struct, thread_info.preempt_count));
>>>>>     #ifdef CONFIG_ARM64_SW_TTBR0_PAN
>>>>>