Re: i386 lazy pmap switching in trap.c

[David Laight <david%l8s.co.uk@localhost>]

On Sat, Feb 09, 2008 at 09:32:44PM +0900, YAMAMOTO Takashi wrote:
> > On Fri, Feb 08, 2008 at 09:14:44PM +0000, David Laight wrote:
> > > On Fri, Feb 08, 2008 at 08:00:17PM +0000, David Laight wrote:
> > > > Am I missing something?
> > > 
> > > Yes ... we need that pmap_load() because we've (probably) slept in
> > > uvm_fault().
> > 
> > Related though, why the retry loop in DO_DEFERRED_SWITCH_RETRY ?
> > 
> >     David
> > 
> > -- 
> > David Laight: david%l8s.co.uk@localhost
> 
> the intention of the loop was to be friendly with future in-kernel preemption.
> onfault_handler() can't detect if the lwp is preempted during pmap_load().

Ah - except that isn't going to work - since the pre-emption can happen
during the copyout itself.
Unless you make every pre-emption check the onfault_handler() address list.

It might be better to be able to mark the lwp as needing its pmap activated.
Then copying/out would lock the pmap active at the top, and release it
at the bottom. Context switch would load the pmap if the flag was set.
(ie you force the non-lazy loading of %cr3)

        David

-- 
David Laight: david%l8s.co.uk@localhost