Re: MIPS: We need to clear MMU contexts of all other processes when asid_cache(cpu) wraps to 0.

[Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>]

On 07/10/2016 06:04 AM, yhb@ruijie.com.cn wrote:
> Subject: [PATCH] MIPS: We need to clear MMU contexts of all other processes
>   when asid_cache(cpu) wraps to 0.
>
> Suppose that asid_cache(cpu) wraps to 0 every n days.
> case 1:
> (1)Process 1 got ASID 0x101.
> (2)Process 1 slept for n days.
> (3)asid_cache(cpu) wrapped to 0x101, and process 2 got ASID 0x101.
> (4)Process 1 is woken,and ASID of process 1 is same as ASID of process 2.
>
> case 2:
> (1)Process 1 got ASID 0x101 on CPU 1.
> (2)Process 1 migrated to CPU 2.
> (3)Process 1 migrated to CPU 1 after n days.
> (4)asid_cache on CPU 1 wrapped to 0x101, and process 2 got ASID 0x101.
> (5)Process 1 is scheduled, and ASID of process 1 is same as ASID of process 2.
>
> So we need to clear MMU contexts of all other processes when asid_cache(cpu) wraps to 0.
>
> Signed-off-by: yhb <yhb@ruijie.com.cn>
>
I think a more clear description should be given here - there is no 
indication that wrap happens over 32bit integer.

And taking into account "n days" frequency - can we just kill all local 
ASIDs in all processes (additionally to local_flush_tlb_all) and enforce 
reassignment if wrap happens? It should be a very rare event, you are 
first to hit this.

It seems to be some localized stuff in get_new_mmu_context() instead of 
widespread patching.

- Leonid.