[RFC PATCH 3/5] powerpc/64s: add CONFIG_PPC_NMMU for nest MMU support

[Nicholas Piggin]

Excerpts from Christophe Leroy's message of December 20, 2020 9:43 pm:
> 
> 
> Le 20/12/2020 à 00:48, Nicholas Piggin a écrit :
>> This allows some nest MMU features to be compiled away if coprocessor
>> support is not selected.
>> 
>> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
>> ---
>>   arch/powerpc/Kconfig                          | 1 +
>>   arch/powerpc/include/asm/book3s/64/mmu.h      | 2 ++
>>   arch/powerpc/include/asm/book3s/64/tlbflush.h | 2 ++
>>   arch/powerpc/include/asm/mmu_context.h        | 5 +++--
>>   arch/powerpc/platforms/Kconfig                | 3 +++
>>   arch/powerpc/platforms/powernv/Kconfig        | 1 +
>>   6 files changed, 12 insertions(+), 2 deletions(-)
>> 
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index ae7391627054..4376bf4c53b4 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -888,6 +888,7 @@ config PPC_PROT_SAO_LPAR
>>   
>>   config PPC_COPRO_BASE
>>   	bool
>> +	select PPC_NMMU if PPC_BOOK3S_64
>>   
>>   config SCHED_SMT
>>   	bool "SMT (Hyperthreading) scheduler support"
>> diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
>> index 995bbcdd0ef8..07850d68a624 100644
>> --- a/arch/powerpc/include/asm/book3s/64/mmu.h
>> +++ b/arch/powerpc/include/asm/book3s/64/mmu.h
>> @@ -103,8 +103,10 @@ typedef struct {
>>   	/* Number of bits in the mm_cpumask */
>>   	atomic_t active_cpus;
>>   
>> +#ifdef CONFIG_PPC_NMMU
>>   	/* Number of users of the external (Nest) MMU */
>>   	atomic_t copros;
>> +#endif
>>   
>>   	/* Number of user space windows opened in process mm_context */
>>   	atomic_t vas_windows;
>> diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush.h b/arch/powerpc/include/asm/book3s/64/tlbflush.h
>> index 0a7431e954c6..c70a82851f78 100644
>> --- a/arch/powerpc/include/asm/book3s/64/tlbflush.h
>> +++ b/arch/powerpc/include/asm/book3s/64/tlbflush.h
>> @@ -16,8 +16,10 @@ enum {
>>   
>>   static inline bool mm_has_nmmu(struct mm_struct *mm)
>>   {
>> +#ifdef CONFIG_PPC_NMMU
>>   	if (unlikely(atomic_read(&mm->context.copros) > 0))
>>   		return true;
>> +#endif
>>   	return false;
>>   }
>>   
>> diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
>> index d5821834dba9..53eac0cc4929 100644
>> --- a/arch/powerpc/include/asm/mmu_context.h
>> +++ b/arch/powerpc/include/asm/mmu_context.h
>> @@ -143,6 +143,7 @@ static inline void dec_mm_active_cpus(struct mm_struct *mm)
>>   	atomic_dec(&mm->context.active_cpus);
>>   }
>>   
>> +#ifdef CONFIG_PPC_NMMU
>>   static inline void mm_context_add_copro(struct mm_struct *mm)
>>   {
>>   	/*
>> @@ -187,6 +188,7 @@ static inline void mm_context_remove_copro(struct mm_struct *mm)
>>   			dec_mm_active_cpus(mm);
>>   	}
>>   }
>> +#endif
>>   
>>   /*
>>    * vas_windows counter shows number of open windows in the mm
>> @@ -218,8 +220,7 @@ static inline void mm_context_remove_vas_window(struct mm_struct *mm)
>>   #else
>>   static inline void inc_mm_active_cpus(struct mm_struct *mm) { }
>>   static inline void dec_mm_active_cpus(struct mm_struct *mm) { }
>> -static inline void mm_context_add_copro(struct mm_struct *mm) { }
>> -static inline void mm_context_remove_copro(struct mm_struct *mm) { }
> 
> Are you sure you can remove those ?
> If so, I think it belongs to another patch, I can't see how the new PPC_NMMU would allow that by itself.

Yeah possibly a separate patch. Nothing except 64s should compile such
code though, I think?

Thanks,
Nick