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Re: I/O permission control in OSKit-Mach

From: Marcus Brinkmann
Subject: Re: I/O permission control in OSKit-Mach
Date: Sat, 8 Dec 2001 23:16:25 +0100
User-agent: Mutt/1.3.23i

On Sat, Oct 20, 2001 at 10:42:35PM -0400, Roland McGrath wrote:
> Indeed.  I think the best plan is to scrutinize the pmap locking strategy
> and do something similar.

I am looking into this, but it looks quite hard.  In fact, it requires an
interrupt to signal the other processors (SMP_IPI_VECTOR == 13 is used for
pmap changes).  Is there a free interrupt that can be used?  Can we
piggyback on the pmap interrupt without increasing the cost for it?

I have only a vague idea how the pmap interrupt stuff works, the comments in
i386/intel/pmap.c helped.  However, they also discouraged me a bit from this
complex solution.

Makes me wonder how Linux behaves, I think that I/O bit mangling is task
based here, but as threads are implemented as tasks, I don't think it works
out there the way we want it to behave for us.

I am inclined to postpone this, and just have a simple lock for the other
races and a #warning for SMP machines, that other cpus will only pick it up
after they are rescheduled.


`Rhubarb is no Egyptian god.' Debian http://www.debian.org brinkmd@debian.org
Marcus Brinkmann              GNU    http://www.gnu.org    marcus@gnu.org

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