Re: [Linux-ia64] Patch to fix lfetches accessing beyond a page (copy_page/clear_pa

[David Mosberger <davidm@napali.hpl.hp.com>]

>>>>> On Wed, 17 Apr 2002 11:51:15 -0700, "Mallick, Asit K" <asit.k.mallick@intel.com> said:

  Asit> Here is a patch fix the lfetches accessing beyond a page that
  Asit> can have a side effect of generating an MCA if the physical
  Asit> memory does not exist. For example, copy_page will try to
  Asit> access video memory for the page that ends at 640K and this
  Asit> can cause MCA for some platforms. Some of the Bigsur UP boot
  Asit> failures were root caused to this problem.

  Asit> Both copy page and clear_page are very performance critical
  Asit> functions and tuned for both Itanium and McKinley. The patch
  Asit> is implemented using unused slots (nops) and has no
  Asit> performance impact.

  Asit> For kernels 2.4.18 and higher you will just need the patch for
  Asit> copy_page().  clear_page and McKinley optimized copy_page has
  Asit> been already taken care.

This patch only papers over the real problem, which is that there
shouldn't be a WB translation covering anything other than normal
memory in the first place.  I don't want to apply hack upon hack, just
so it works for another while.  Let's fix this one permanently.  I
think we may just have to bite the bullet and treat the <64MB
specially in the alternate TLB handlers.  If we use a 4KB page size
for that area, we should be good (assuming DIG goes ahead and does
something sane about requiring a minimum granularity for physical
memory).

	--david