Re: [RFC PATCH 02/14] sparc64: add new fields to mmu context for shared context support

From: Mike Kravetz
Date: Sun Dec 18 2016 - 18:46:57 EST


On 12/16/2016 11:38 PM, Sam Ravnborg wrote:
> Hi Mike
>
>> diff --git a/arch/sparc/include/asm/mmu_context_64.h b/arch/sparc/include/asm/mmu_context_64.h
>> index b84be67..d031799 100644
>> --- a/arch/sparc/include/asm/mmu_context_64.h
>> +++ b/arch/sparc/include/asm/mmu_context_64.h
>> @@ -35,15 +35,15 @@ void __tsb_context_switch(unsigned long pgd_pa,
>> static inline void tsb_context_switch(struct mm_struct *mm)
>> {
>> __tsb_context_switch(__pa(mm->pgd),
>> - &mm->context.tsb_block[0],
>> + &mm->context.tsb_block[MM_TSB_BASE],
>> #if defined(CONFIG_HUGETLB_PAGE) || defined(CONFIG_TRANSPARENT_HUGEPAGE)
>> - (mm->context.tsb_block[1].tsb ?
>> - &mm->context.tsb_block[1] :
>> + (mm->context.tsb_block[MM_TSB_HUGE].tsb ?
>> + &mm->context.tsb_block[MM_TSB_HUGE] :
>> NULL)
>> #else
>> NULL
>> #endif
>> - , __pa(&mm->context.tsb_descr[0]));
>> + , __pa(&mm->context.tsb_descr[MM_TSB_BASE]));
>> }
>>
> This is a nice cleanup that has nothing to do with your series.
> Could you submit this as a separate patch so we can get it applied.
>
> This is the only place left where the array index for tsb_block
> and tsb_descr uses hardcoded values. And it would be good to get
> rid of these.

Sure, I will submit a separate cleanup patch for this.

However, do note that in my series if CONFIG_SHARED_MMU_CTX is defined,
then MM_TSB_HUGE_SHARED is index 0, instead of MM_TSB_BASE being 0 in
the case where CONFIG_SHARED_MMU_CTX is not defined. This may seem
'strange' and the obvious question would be 'why not put CONFIG_SHARED_MMU_CTX
at the end of the existing array (index 2)?'. The reason is that tsb_descr
array can not have any 'holes' when passed to the hypervisor. Since there
will always be a MM_TSB_BASE tsb, with MM_TSB_HUGE_SHARED before and
MM_TSB_HUGE after MM_TSB_BASE, few tricks are necessary to ensure no holes
are in the array passed to the hypervisor.

--
Mike Kravetz