Subject: Re: Kernel copyin/out optimizations for ARM...
To: David Laight <>
From: Richard Earnshaw <>
List: port-arm
Date: 03/12/2002 11:57:25
> On Tue, Mar 12, 2002 at 10:38:39AM +0000, Richard Earnshaw wrote:
> > 
> > I've always wondered why that code wasn't written using ldrt/strt for the 
> > user-space accesses.  That would then use the hardware for permission 
> > checking and eliminate the most expensive part of that code (doing the tlb 
> > check manually).
> not in ARM v3?

Nope; even the ARM2 had these IIRC.

> > 
> > Maybe there is some reason why that would not work (wrong page tables 
> > mapped?)
> Isn't there a problem that the cache is checked before the TLBs?
> Maybe bound checking the address is enough?

I don't think so.  The instructions are defined to work as though a user 
privilaged process had run the instruction.

> Why did the 'move from/to previous address space' instructions that
> the pdp-11 have disappear from most later systems?

Never used a pdp-11....  I'm not THAT old :-)