Re: [RFC 01/20] mm/tlb: fix fullmm semantics

[Nadav Amit]

> On Feb 3, 2021, at 1:44 AM, Will Deacon <will@xxxxxxxxxx> wrote:
> 
> On Tue, Feb 02, 2021 at 01:35:38PM -0800, Nadav Amit wrote:
>>> On Feb 2, 2021, at 3:00 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>>> 
>>> On Tue, Feb 02, 2021 at 01:32:36AM -0800, Nadav Amit wrote:
>>>>> On Feb 1, 2021, at 3:36 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>>>>> 
>>>>> 
>>>>> https://lkml.kernel.org/r/20210127235347.1402-1-will@xxxxxxxxxx
>>>> 
>>>> I have seen this series, and applied my patches on it.
>>>> 
>>>> Despite Will’s patches, there were still inconsistencies between fullmm
>>>> and need_flush_all.
>>>> 
>>>> Am I missing something?
>>> 
>>> I wasn't aware you were on top. I'll look again.
>> 
>> Looking on arm64’s tlb_flush() makes me think that there is currently a bug
>> that this patch fixes. Arm64’s tlb_flush() does:
>> 
>>       /*
>>        * If we're tearing down the address space then we only care about
>>        * invalidating the walk-cache, since the ASID allocator won't
>>        * reallocate our ASID without invalidating the entire TLB.
>>        */
>>       if (tlb->fullmm) {
>>               if (!last_level)
>>                       flush_tlb_mm(tlb->mm);
>>               return;
>>       } 
>> 
>> But currently tlb_mmu_finish() can mistakenly set fullmm incorrectly (if
>> mm_tlb_flush_nested() is true), which might skip the TLB flush.
> 
> But in that case isn't 'freed_tables' set to 1, so 'last_level' will be
> false and we'll do the flush in the code above?

Indeed. You are right. So no rush.