[Xen-changelog] [xen-unstable] x86/mm: refine epte_present test

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Tim Deegan <tim@xxxxxxx>
# Date 1326978563 0
# Node ID 2273ef2083d4a369044bdd8677635e0c0c3ae594
# Parent  f5b366c6c4c6a19f93f0c68dc9fc939f172ec908
x86/mm: refine epte_present test

The current test for a present ept entry checks for a permission bit
to be set.

While this is valid in contexts in which we want to know whether an entry
will fault, it is not correct when it comes to testing whether an entry is
valid. Specifically, in the ept_change_entry_type_page function which is
used to set entries to the log dirty type.

In combination with a p2m access type like n or n2rwx, log dirty will not be
set for ept entries for which it should.

Reported-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
Signed-off-by: Tim Deegan <tim@xxxxxxx>
Acked-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
Committed-by: Tim Deegan <tim@xxxxxxx>
---


diff -r f5b366c6c4c6 -r 2273ef2083d4 xen/arch/x86/mm/p2m-ept.c
--- a/xen/arch/x86/mm/p2m-ept.c Thu Jan 19 10:42:42 2012 +0000
+++ b/xen/arch/x86/mm/p2m-ept.c Thu Jan 19 13:09:23 2012 +0000
@@ -41,6 +41,10 @@
 
 #define is_epte_present(ept_entry)      ((ept_entry)->epte & 0x7)
 #define is_epte_superpage(ept_entry)    ((ept_entry)->sp)
+static inline bool_t is_epte_valid(ept_entry_t *e)
+{
+    return (e->epte != 0 && e->sa_p2mt != p2m_invalid);
+}
 
 /* Non-ept "lock-and-check" wrapper */
 static int ept_pod_check_and_populate(struct p2m_domain *p2m, unsigned long 
gfn,
@@ -777,7 +781,7 @@
 
     for ( int i = 0; i < EPT_PAGETABLE_ENTRIES; i++ )
     {
-        if ( !is_epte_present(epte + i) )
+        if ( !is_epte_valid(epte + i) )
             continue;
 
         if ( (ept_page_level > 0) && !is_epte_superpage(epte + i) )

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