[Xen-devel] [PATCH 1 of 3] p2m: Allow l2 pages to be replaced by superpages

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

# HG changeset patch
# User George Dunlap <george.dunlap@xxxxxxxxxxxxx>
# Date 1295274250 0
# Node ID 366d675630fd6ecbd6228426b3f7723d8a9dd944
# Parent  75b6287626ee0b852d725543568001e99b13be5b
p2m: Allow l2 pages to be replaced by superpages

Allow second-level p2m pages to be replaced with superpage entries,
freeing the p2m table page properly.  This allows, for example, a
sequence of 512 singleton zero pages to be replaced with a superpage
populate-on-demand entry.

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

diff -r 75b6287626ee -r 366d675630fd xen/arch/x86/mm/hap/hap.c
--- a/xen/arch/x86/mm/hap/hap.c Fri Jan 14 16:38:51 2011 +0000
+++ b/xen/arch/x86/mm/hap/hap.c Mon Jan 17 14:24:10 2011 +0000
@@ -333,9 +333,11 @@
 
     ASSERT(page_get_owner(pg) == d);
     /* Should have just the one ref we gave it in alloc_p2m_page() */
-    if ( (pg->count_info & PGC_count_mask) != 1 )
-        HAP_ERROR("Odd p2m page count c=%#lx t=%"PRtype_info"\n",
-                  pg->count_info, pg->u.inuse.type_info);
+    if ( (pg->count_info & PGC_count_mask) != 1 ) {
+        HAP_ERROR("Odd p2m page %p count c=%#lx t=%"PRtype_info"\n",
+                     pg, pg->count_info, pg->u.inuse.type_info);
+        WARN();
+    }
     pg->count_info &= ~PGC_count_mask;
     /* Free should not decrement domain's total allocation, since
      * these pages were allocated without an owner. */
diff -r 75b6287626ee -r 366d675630fd xen/arch/x86/mm/hap/p2m-ept.c
--- a/xen/arch/x86/mm/hap/p2m-ept.c     Fri Jan 14 16:38:51 2011 +0000
+++ b/xen/arch/x86/mm/hap/p2m-ept.c     Mon Jan 17 14:24:10 2011 +0000
@@ -317,6 +317,7 @@
     int vtd_pte_present = 0;
     int needs_sync = 1;
     struct domain *d = p2m->domain;
+    struct page_info *intermediate_table = NULL;
 
     /*
      * the caller must make sure:
@@ -369,6 +370,12 @@
         /* No need to flush if the old entry wasn't valid */
         if ( !is_epte_present(ept_entry) )
             needs_sync = 0;
+        else if ( order == 9 && ! ept_entry->sp )
+        {
+            /* We're replacing a non-SP page with a superpage.  Make sure to
+             * handle freeing the table properly. */
+            intermediate_table = mfn_to_page(ept_entry->mfn);
+        }
 
         if ( mfn_valid(mfn_x(mfn)) || direct_mmio || p2m_is_paged(p2mt) ||
              (p2mt == p2m_ram_paging_in_start) )
@@ -487,6 +494,17 @@
         }
     }
 
+    if ( intermediate_table )
+    {
+        /* Release the old intermediate table.  This has to be the
+           last thing we do, after the ept_sync_domain() and removal
+           from the iommu tables, so as to avoid a potential
+           use-after-free. */
+
+        page_list_del(intermediate_table, &d->arch.p2m->pages);
+        d->arch.paging.free_page(d, intermediate_table);
+    }
+
     return rv;
 }
 
diff -r 75b6287626ee -r 366d675630fd xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c     Fri Jan 14 16:38:51 2011 +0000
+++ b/xen/arch/x86/mm/p2m.c     Mon Jan 17 14:24:10 2011 +0000
@@ -1361,9 +1361,15 @@
         if ( (l1e_get_flags(*p2m_entry) & _PAGE_PRESENT) &&
              !(l1e_get_flags(*p2m_entry) & _PAGE_PSE) )
         {
-            P2M_ERROR("configure P2M table 4KB L2 entry with large page\n");
-            domain_crash(p2m->domain);
-            goto out;
+            struct page_info *pg;
+
+            /* We're replacing a non-SP page with a superpage.  Make sure to
+             * handle freeing the table properly. */
+            pg = mfn_to_page(_mfn(l1e_get_pfn(*p2m_entry)));
+            paging_write_p2m_entry(p2m->domain, gfn, p2m_entry, table_mfn,
+                                   l1e_empty(), 2);
+            page_list_del(pg, &p2m->pages);
+            p2m->domain->arch.paging.free_page(p2m->domain, pg);
         }
         
         ASSERT(!mfn_valid(mfn) || p2mt != p2m_mmio_direct);

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