Re: [patch 0/4] x86: PAT followup - Incremental changes and bug fixes

["Andreas Herrmann3" <andreas.herrmann3@amd.com>]

On Thu, Jan 17, 2008 at 11:15:05PM +0100, Ingo Molnar wrote:
> 
> * Andreas Herrmann3 <andreas.herrmann3@AMD.COM> wrote:
> 
> > On Thu, Jan 17, 2008 at 10:42:09PM +0100, Ingo Molnar wrote:
> > > 
> > > * Siddha, Suresh B <suresh.b.siddha@intel.com> wrote:
> > > 
> > > > On Thu, Jan 17, 2008 at 10:13:08PM +0100, Ingo Molnar wrote:
> > > > > but in general we must be robust enough in this case and just degrade 
> > > > > any overlapping page to UC (and emit a warning perhaps) - instead of 
> > > > > failing the ioremap and thus failing the driver (and the bootup).
> > > > 
> > > > But then, this will cause an attribute conflicit. Old one was 
> > > > specifying WB in PAT (ioremap with noflags) and the new ioremap 
> > > > specifies UC.
> > > 
> > > we could fix up all aliases of that page as well and degrade them to UC?
> > 
> > Yes, we must fix all aliases or reject the conflicting mapping. But 
> > fixing all aliases might not be that easy. (I've just seen a panic 
> > when using your patch ;-(
> 
> yes, indeed my patch is bad if you have PAT enabled: conflicting cache 
> attributes might be present. I'll go with your patch for now.

I think the best is to just reject conflicting mappings. (Because now
I am too tired to think about a safe way how to change the aliases to the
most restrictive memory type. ;-)

But then of course such boot-time problems like I've seen on my test
machines should be avoided somehow.


Andreas