[Xen-changelog] Added extra shadow_sync_mfn() in do_update_va_mapping to deal

[BitKeeper Bot <riel@xxxxxxxxxxx>]

ChangeSet 1.1236.32.8, 2005/03/16 01:14:39+00:00, mafetter@xxxxxxxxxxxxxxxx

        Added extra shadow_sync_mfn() in do_update_va_mapping to deal
        with a shortcoming of the checking code in _check_pagetable.
        Better to have a few more flushes and checking code that can
        still be used.  It would be even better to have smarter checking
        code, but that will take more time.
        
        Signed-off-by: michael.fetterman@xxxxxxxxxxxx



 arch/x86/mm.c            |   25 +++++++++++++++++++++++++
 include/xen/perfc_defn.h |    1 +
 2 files changed, 26 insertions(+)


diff -Nru a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c 2005-04-05 12:09:52 -04:00
+++ b/xen/arch/x86/mm.c 2005-04-05 12:09:52 -04:00
@@ -2001,6 +2001,8 @@
     }
     else
     {
+        unsigned long l1mfn;
+
         if ( unlikely(percpu_info[cpu].foreign &&
                       (shadow_mode_translate(d) ||
                        shadow_mode_translate(percpu_info[cpu].foreign))) )
@@ -2020,6 +2022,29 @@
         // linear_pg_table[l1_linear_offset(va)] to be in sync)...
         //
         __shadow_sync_va(ed, va);
+
+#if 1 /* keep check_pagetables() happy */
+        /*
+         * However, the above doesn't guarantee that there's no snapshot of
+         * the L1 table in question; it just says that the relevant L2 and L1
+         * entries for VA are in-sync.  There might still be a snapshot.
+         *
+         * The checking code in _check_pagetables() assumes that no one will
+         * mutate the shadow of a page that has a snapshot.  It's actually
+         * OK to not sync this page, but it seems simpler to:
+         * 1) keep all code paths the same, and
+         * 2) maintain the invariant for _check_pagetables(), rather than try
+         *    to teach it about this boundary case.
+         * So we flush this L1 page, if it's out of sync.
+         */
+        l1mfn = (l2_pgentry_val(linear_l2_table(ed)[l2_table_offset(va)]) >>
+                 PAGE_SHIFT);
+        if ( mfn_out_of_sync(l1mfn) )
+        {
+            perfc_incrc(extra_va_update_sync);
+            __shadow_sync_mfn(d, l1mfn);
+        }
+#endif /* keep check_pagetables() happy */
 
         if ( unlikely(__put_user(val, &l1_pgentry_val(
                                      linear_pg_table[l1_linear_offset(va)]))) )
diff -Nru a/xen/include/xen/perfc_defn.h b/xen/include/xen/perfc_defn.h
--- a/xen/include/xen/perfc_defn.h      2005-04-05 12:09:52 -04:00
+++ b/xen/include/xen/perfc_defn.h      2005-04-05 12:09:52 -04:00
@@ -50,6 +50,7 @@
 PERFCOUNTER_CPU(shadow_make_snapshot,              "snapshots created")
 PERFCOUNTER_CPU(shadow_mark_mfn_out_of_sync_calls, "calls to 
shadow_mk_out_of_sync")
 PERFCOUNTER_CPU(shadow_out_of_sync_calls,          "calls to 
shadow_out_of_sync")
+PERFCOUNTER_CPU(extra_va_update_sync,              "extra syncs for bug in 
chk_pgtb")
 PERFCOUNTER_CPU(snapshot_entry_matches_calls,      "calls to ss_entry_matches")
 PERFCOUNTER_CPU(snapshot_entry_matches_true,       "ss_entry_matches returns 
true")
 

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