Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v2 1/7] arm64: add CPU field to struct thread_info
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Keith Packard <keithpac@amazon.com>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Heiko Carstens <hca@linux.ibm.com>,
        Mark Rutland <mark.rutland@arm.com>
References: <20210930125813.197418-1-ardb@kernel.org>
 <20210930125813.197418-2-ardb@kernel.org>
 <6b003f58-48df-7ac4-4dbf-81b2c5bca5d9@csgroup.eu>
 <CAMj1kXECGp=5QRQS8HQNfE6RyA=eQfRiciDdjXp_ucpk8OxkDQ@mail.gmail.com>
 <f634b2fe-3d89-709b-a56e-7da08af3988e@csgroup.eu>
 <CAMj1kXFuzDSxbE7OTV0Sb5UYaGQ5v_yFeq8LYE--kZ_AffaB4g@mail.gmail.com>
From:   Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <f9362e71-0a2a-ffa8-b428-d52fed7b5228@csgroup.eu>
Date:   Thu, 30 Sep 2021 15:23:10 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.11.0
MIME-Version: 1.0
In-Reply-To: <CAMj1kXFuzDSxbE7OTV0Sb5UYaGQ5v_yFeq8LYE--kZ_AffaB4g@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: fr-FR
Content-Transfer-Encoding: 8bit
Precedence: bulk


Le 30/09/2021 à 15:20, Ard Biesheuvel a écrit :
> On Thu, 30 Sept 2021 at 15:15, Christophe Leroy
> <christophe.leroy@csgroup.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@csgroup.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@kernel.org>
>>>>> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
>>>>> Acked-by: Mark Rutland <mark.rutland@arm.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
>>>>>