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Re: [PATCH] MIPS: ASID conflict after CPU hotplug

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: [PATCH] MIPS: ASID conflict after CPU hotplug
From: "Kevin D. Kissell" <kevink@paralogos.com>
Date: Mon, 22 Nov 2010 13:34:38 -0800
Cc: Maksim Rayskiy <maksim.rayskiy@gmail.com>, linux-mips@linux-mips.org
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On 11/21/10 19:41, Ralf Baechle wrote:
...
Need to think a little about potencial consequences of your suggested
patch.  It seems ok.  Kevin, what do you think?
Since you ask, while I would imagine that Maksim's patch works fine for him, I'm not sure that it's really the right fix. I never did succeed in getting CPU hotplugging working back in the 2.6.18 days, so I don't know as much about it as I'd like, but if per_cpu_trap_init() needs to be invoked on a hot plugin event, and if its behavior needs to be different , I'd really, really prefer to see that state propagated explicitly, rather than inferring it from whatever happens to be in cache/memory at cpu_data[cpu].asid_cache. But beyond that, if the problem arises because setting cpu_data[cpu].asid_cache to a known initial state on a plugin event can conflict with the residual content of EntryHi, rather than creating a special case where we don't initialize the ASID cache, since we seem to be (re)initializing a lot of other privileged state, why aren't we also setting a known sane initial EntryHi value? Wouldn't that be a cleaner fix? (And I don't mean that as a rhetorical question - there may be very good reasons to let EntryHi values persist across hot unplug/plug events. I just can't imagine them offhand over coffee.)

/K.


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