[Xen-changelog] [xen-unstable] x86: avoid EPT scanning errors when splitting superpages during live migration

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1239970026 -3600
# Node ID 150662e5adfc9a8f95329f037432d76a92247aae
# Parent  b920a2f799d960c492eefcedde0fde1e7793e7df
x86: avoid EPT scanning errors when splitting superpages during live migration

Since Xen did not lock the p2m table for p2m table reading, when
splitting the large page during live migration, we should make sure
the path of EPT entries be modified are always there while other CPUs
may access the super entries at the same time.

Signed-off-by: Xin, Xiaohui <xiaohui.xin@xxxxxxxxx>
---
 xen/arch/x86/mm/hap/p2m-ept.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff -r b920a2f799d9 -r 150662e5adfc xen/arch/x86/mm/hap/p2m-ept.c
--- a/xen/arch/x86/mm/hap/p2m-ept.c     Fri Apr 17 13:04:47 2009 +0100
+++ b/xen/arch/x86/mm/hap/p2m-ept.c     Fri Apr 17 13:07:06 2009 +0100
@@ -210,17 +210,18 @@ ept_set_entry(struct domain *d, unsigned
         ept_entry_t *split_ept_entry = NULL;
         unsigned long split_mfn = ept_entry->mfn;
         p2m_type_t split_p2mt = ept_entry->avail1;
+        ept_entry_t new_ept_entry;
 
         /* alloc new page for new ept middle level entry which is
          * before a leaf super entry
          */
 
-        if ( !ept_set_middle_entry(d, ept_entry) )
+        if ( !ept_set_middle_entry(d, &new_ept_entry) )
             goto out;
 
         /* split the super page before to 4k pages */
 
-        split_table = map_domain_page(ept_entry->mfn);
+        split_table = map_domain_page(new_ept_entry.mfn);
         offset = gfn & ((1 << EPT_TABLE_ORDER) - 1);
 
         for ( i = 0; i < 512; i++ )
@@ -257,6 +258,7 @@ ept_set_entry(struct domain *d, unsigned
         ept_p2m_type_to_flags(split_ept_entry, p2mt);
 
         unmap_domain_page(split_table);
+        *ept_entry = new_ept_entry;
     }
 
     /* Track the highest gfn for which we have ever had a valid mapping */

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