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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