Hi Leonid, On Mon, Jul 11, 2016 at 11:02:00AM -0700, Leonid Yegoshin wrote: > On 07/10/2016 06:04 AM, yhb@xxxxxxxxxxxxx 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@xxxxxxxxxxxxx> > > > 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. That is what this patch does, but to do so it appears you need to lock the other tasks one by one, and that must be doable from a context switch, i.e. hardirq context, and that requires the task lock to be of the _irqsave variant, hence the widespread changes and the relatively tiny MIPS change hidden in the middle. Cheers James
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