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[Xen-devel] Debugging PAE Xen with >4GB

  • To: "xen-devel" <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
  • Date: Fri, 16 Jun 2006 16:43:02 -0700
  • Delivery-date: Fri, 16 Jun 2006 16:43:32 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcaRnptK2CNywpwEQn+OjoZoehS6RA==
  • Thread-topic: Debugging PAE Xen with >4GB

I just did some debugging on PAE SMP dom0 with Xen on a machine with
>4GB memory. As far as we tested, PAE SMP dom0 hangs on machines with
>4GB (latest, changeset: 10363:61a81fab2a02).

Now it works fines with the patch below. I don't think this is the final
patch, but it's a hint for debugging (for Keir, especially ;-). If I
back out the patch, what I see is that the second level page table for
mapping Xen is not valid, i.e. zero clean (L3 looks okay). So debug Xen
works fine (i.e. the one built by "make debug=y").

diff -r 61a81fab2a02 xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c Fri Jun 16 14:34:21 2006
+++ b/xen/arch/x86/mm.c Fri Jun 16 16:44:39 2006
@@ -258,11 +258,6 @@
 #if defined(CONFIG_X86_PAE)
-#ifdef NDEBUG
-/* Only PDPTs above 4GB boundary need to be shadowed in low memory. */
-#define l3tab_needs_shadow(mfn) (mfn >= 0x100000)
  * In debug builds we aggressively shadow PDPTs to exercise code paths.
  * We cannot safely shadow the idle page table, nor shadow-mode page
@@ -272,7 +267,6 @@
     ((((mfn << PAGE_SHIFT) != __pa(idle_pg_table)) &&   \
       (page_get_owner(mfn_to_page(mfn)) != NULL)) ||    \
      (mfn >= 0x100000))
 static l1_pgentry_t *fix_pae_highmem_pl1e;

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