Is pmap_kextract() allowed to fault?

[Marcel Moolenaar]

On Mon, Apr 21, 2003 at 09:24:49AM -0400, Jake Burkholder wrote:
> Apparently, On Sun, Apr 20, 2003 at 10:53:32PM -0700,
> 	Marcel Moolenaar said words to the effect of;
> 
> > Gang,
> > 
> > On ia64 pmap_kextract() uses the tpa instruction which given a
> > virtual address returns the physical address based on the
> > translation registers and cache (ie TLB). This can fault when
> > there's currently no mapping for the virtual address.
> > 
> > Since all other architectures have a non-faulting implementation
> > (AFAICT), I'm a bit worried that we might get into trouble on
> > ia64. I couldn't find anything about pmap_kextract(), so maybe
> > anybody can enlighten me:
> > 
> > 1. Is pmap_kextract() allowed to fault?
> 
> It depends what kind of fault.  Will tpa fail if it causes a tlb fault
> and the page is not in the vhpt (or whatever the fault handler searches),
> or will it end up calling vm_fault and actually trying to fault in the
> page?

It will end up calling vm_fault() if so required.

> > 2. Is pmap_kextract() used often enough that using the cpu's TLB
> >    is a possible performance speedup even if there are costly faults
> >    that can sometimes happen?
> 
> I doubt it.

Ok, thanks. I think I'll use a non-trapping implementation then.
There's just too much circumstantiality...

-- 
 Marcel Moolenaar	  USPA: A-39004		 marcel at xcllnt.net