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

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Date:   Thu, 30 Sep 2021 15:20:41 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
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

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?

> >
> >
> >>>      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
> >>>