From: Bhavna Sarathy <bnagendr@redhat.com>
Date: Fri, 19 Jun 2009 13:42:36 -0400
Subject: [xen] disable 2MB support on PAE kernels
Message-id: 20090619174248.16950.77533.sendpatchset@allegro.boston.redhat.com
O-Subject: [RHEL5.4 PATCH] [Xen] Disable 2MB support on PAE kernels
Bugzilla: 503737
RH-Acked-by: Don Dutile <ddutile@redhat.com>
RH-Acked-by: Rik van Riel <riel@redhat.com>
RH-Acked-by: Chris Lalancette <clalance@redhat.com>
RH-Acked-by: Justin M. Forbes <jforbes@redhat.com>

Resolves BZ 503737

Chris Lalancette found a bug where the RHEL5.4 FV i686 -PAE kernel guest
was hanging.   We root caused this to the 2MB supports that is dependent on
Nested Paging, however on the PAE kernels Nested Paging is diabled due
to a hardware limitation.

So the fix is to disable 2MB when Nested Paging is disabled.  It's a simple
patch.

AMD has tested the following test matrix (both 2MB and 1GB).  Chris has
tested the patch on his system.

Guests:
     windows XP 32bit 1G, 6G (guest will see 4G only)
     RHEL 5.3 32bit 1G, 6G (guest will see 4G only)
     RHEL 5.3 PAE 1G, 6G
     RHEL 5.4 64bit 1G, 6G (won't work on kernel Xen PAE) Kernel Xen PAE
    - hap=0, hap_1gb=0
    - hap=1, hap_1gb=0
    - hap=0, hap_1gb=1
    - hap=1, hap_1gb=1
Kernel Xen 64bit
    - hap=0, hap_1gb=0
    - hap=1, hap_1gb=0
    - hap=0, hap_1gb=1
    - hap=1, hap_1gb=1

The issue exists upstream and has been submitted.
http://article.gmane.org/gmane.comp.emulators.xen.devel/67674

Please review and ACK.

diff --git a/arch/x86/mm/p2m.c b/arch/x86/mm/p2m.c
index dd45d70..767d483 100644
--- a/arch/x86/mm/p2m.c
+++ b/arch/x86/mm/p2m.c
@@ -412,9 +412,13 @@ int set_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
     while ( todo )
     {
         /* decide which page mode to use */
-        order = ( (((gfn | mfn_x(mfn) | todo) & ((1ul << 18) - 1)) == 0) &&
-                  hap_1gb_pgtb(d) && opt_hap_1gb ) ? 18 :
-            (((gfn | mfn_x(mfn) | todo) & ((1ul << 9) - 1)) == 0) ? 9 : 0;
+	if ( hap_enabled(d) )
+		order = ( (((gfn | mfn_x(mfn) | todo) & ((1ul << 18) - 1)) == 0) &&
+		hap_1gb_pgtb(d) && opt_hap_1gb ) ? 18 :
+		(((gfn | mfn_x(mfn) | todo) & ((1ul << 9) - 1)) == 0) ? 9 : 0;
+	else
+		order = 0;
+
         rc = d->arch.p2m.set_entry(d, gfn, mfn, order, l1e_flags);
         gfn += 1ul << order;
         if ( mfn_x(mfn) != INVALID_MFN )