Message-ID: <5783DFF5.3060401@imgtec.com>
Date: Mon, 11 Jul 2016 11:05:41 -0700
From: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
MIME-Version: 1.0
Subject: [PATCH] MIPS: We need to clear MMU contexts of all other processes
 when asid_cache(cpu) wraps to 0.
References: <80B78A8B8FEE6145A87579E8435D78C30205D5F3@fzex.ruijie.com.cn> <5783DF18.1080408@imgtec.com>
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To: yhb@ruijie.com.cn, ralf@linux-mips.org
Cc: linux-mips@linux-mips.org
Message-ID: <20160711180541.P_GJY9LY9m4apzDQSvWTfsuOdb2bjH05HNjZ2sa6YfE@z>

> 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