Re: another new version of pageattr caching conflict fix for 2.4

From: Andi Kleen (ak@suse.de)
Date: Sun Jun 16 2002 - 18:37:32 EST


> > MTRRs work on physical, not virtual memory, so they have no aliasing
> > issues.
>
> Doesn't the AGP aperture cause a physical alias? Leading to strange

Yes. That's what this patch is all about.

> the same problems if the agp aperture was marked write-back, and the

AGP aperture is uncacheable, not write-back.

> memory was marked uncacheable. My gut impression is to just make the
> agp aperture write-back cacheable, and then we don't have to change
> the kernel page table at all. Unfortunately I don't expect the host

That would violate the AGP specification.

> bridge with the memory and agp controllers to like that mode,
> especially as there are physical aliasing issues.

exactly.

>
> > Fixing the MTRRs is fine, but it is really outside the scope of my patch.
> > Just changing the kernel map wouldn't be enough to fix wrong MTRRs,
> > because it wouldn't cover highmem.
>
> My preferred fix is to use PAT, to override the buggy mtrrs. Which
> brings up the same aliasing issues. Which makes it related but
> outside the scope of the problem.

I don't follow you here. IMHO it is much easier to fix the MTRRs in the
MTRR driver for those rare buggy BIOS (if they exist - I've never seen one)
than to hack up all of memory management just to get the right bits set.
I see no disadvantage of using the MTRRs and it is lot simpler than
PAT and pte bits.

-Andi

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This archive was generated by hypermail 2b29 : Sun Jun 23 2002 - 22:00:11 EST