On 07/11/2016 11:07 AM, James Hogan wrote:
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.
Not exactly. The change must be done only for local CPU which executes
at the moment get_new_mmu_context(). Just prevent preemption here and
change of cpu_context(THIS_CPU,...) can be done safely - other CPUs
don't do anything with this variable besides killing it (writing 0 to it).
You can look into flush_tlb_mm() for example how it is cleared for
single memory map.
We have a macro to safely walk all processes, right? (don't remember
it's name).
