Re: [PATCH v2 01/23] asm-generic: add generic MMU versions of mmu context functions

Nicholas Piggin
2020-09-01T07:15:00Z

Excerpts from Mike Rapoport's message of September 1, 2020 4:49 pm:
> On Thu, Aug 27, 2020 at 12:52:27AM +1000, Nicholas Piggin wrote:
>> Many of these are no-ops on many architectures, so extend mmu_context.h
>> to cover MMU and NOMMU, and split the NOMMU bits out to nommu_context.h
>>
>> Cc: Arnd Bergmann <arnd@arndb.de>
>> Cc: linux-arch@vger.kernel.org
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>> arch/microblaze/include/asm/mmu_context.h | 2 +-
>> arch/sh/include/asm/mmu_context.h | 2 +-
>> include/asm-generic/mmu_context.h | 57 +++++++++++++++++------
>> include/asm-generic/nommu_context.h | 19 ++++++++
>> 4 files changed, 64 insertions(+), 16 deletions(-)
>> create mode 100644 include/asm-generic/nommu_context.h
>>
>> diff --git a/arch/microblaze/include/asm/mmu_context.h b/arch/microblaze/include/asm/mmu_context.h
>> index f74f9da07fdc..34004efb3def 100644
>> --- a/arch/microblaze/include/asm/mmu_context.h
>> +++ b/arch/microblaze/include/asm/mmu_context.h
>> @@ -2,5 +2,5 @@
>> #ifdef CONFIG_MMU
>> # include <asm/mmu_context_mm.h>
>> #else
>> -# include <asm-generic/mmu_context.h>
>> +# include <asm-generic/nommu_context.h>
>> #endif
>> diff --git a/arch/sh/include/asm/mmu_context.h b/arch/sh/include/asm/mmu_context.h
>> index f664e51e8a15..461b1304580b 100644
>> --- a/arch/sh/include/asm/mmu_context.h
>> +++ b/arch/sh/include/asm/mmu_context.h
>> @@ -133,7 +133,7 @@ static inline void switch_mm(struct mm_struct *prev,
>> #define set_TTB(pgd) do { } while (0)
>> #define get_TTB() (0)
>>
>> -#include <asm-generic/mmu_context.h>
>> +#include <asm-generic/nommu_context.h>
>>
>> #endif /* CONFIG_MMU */
>>
>> diff --git a/include/asm-generic/mmu_context.h b/include/asm-generic/mmu_context.h
>> index 6be9106fb6fb..86cea80a50df 100644
>> --- a/include/asm-generic/mmu_context.h
>> +++ b/include/asm-generic/mmu_context.h
>> @@ -3,44 +3,73 @@
>> #define __ASM_GENERIC_MMU_CONTEXT_H
>>
>> /*
>> - * Generic hooks for NOMMU architectures, which do not need to do
>> - * anything special here.
>> + * Generic hooks to implement no-op functionality.
>> */
>>
>> -#include <asm-generic/mm_hooks.h>
>> -
>> struct task_struct;
>> struct mm_struct;
>>
>> +/*
>> + * enter_lazy_tlb - Called when "tsk" is about to enter lazy TLB mode.
>> + *
>> + * @mm: the currently active mm context which is becoming lazy
>> + * @tsk: task which is entering lazy tlb
>> + *
>> + * tsk->mm will be NULL
>> + */
>> +#ifndef enter_lazy_tlb
>> static inline void enter_lazy_tlb(struct mm_struct *mm,
>> struct task_struct *tsk)
>> {
>> }
>> +#endif
>>
>> +/**
>> + * init_new_context - Initialize context of a new mm_struct.
>> + * @tsk: task struct for the mm
>> + * @mm: the new mm struct
>
> 'make *docs' will complain here about missing Return: description

Thanks, I added something. Looks like we can't get rid of it, sparc
and um can return error. Oh well.

>> + */
>> +#ifndef init_new_context
>> static inline int init_new_context(struct task_struct *tsk,
>> struct mm_struct *mm)
>> {
>> return 0;
>> }
>> +#endif
>
> Most architectures have non-trivial init_new_context, maybe this
> should go into nommu_context.h?

Hmm, I guess you could go either way. A few do have no-op functions so I
think that qualifies them if the rule is less ambiguous and we provide
no-op for functions unless it does not make any sense (e.g., switch_mm
for MMU). More importantly I already have the code written and am lazy
:)

Thanks,
Nick