diff -r 4b476378fc35 xen/drivers/acpi/tables/tbutils.c
--- a/xen/drivers/acpi/tables/tbutils.c	Mon Jan 21 17:03:10 2013 +0000
+++ b/xen/drivers/acpi/tables/tbutils.c	Tue Jan 22 15:13:43 2013 +0000
@@ -525,3 +525,23 @@
 
 	return_ACPI_STATUS(AE_OK);
 }
+
+acpi_status acpi_tb_get_table_physical_location(char *signature, acpi_physical_address *out_addr, u32 *out_size)
+{
+    acpi_native_uint i;
+
+    if (!signature || !out_addr || !out_size) {
+        return (AE_BAD_PARAMETER);
+    }
+
+    for (i = 0; i < acpi_gbl_root_table_list.count; i++) {
+        if (!ACPI_COMPARE_NAME(&(acpi_gbl_root_table_list.tables[i].signature), signature)) {
+            continue;
+        }
+        *out_addr = acpi_gbl_root_table_list.tables[i].address;
+        *out_size = acpi_gbl_root_table_list.tables[i].length;
+        return AE_OK;
+    }
+    return AE_NOT_FOUND;
+}
+
diff -r 4b476378fc35 xen/drivers/passthrough/vtd/dmar.c
--- a/xen/drivers/passthrough/vtd/dmar.c	Mon Jan 21 17:03:10 2013 +0000
+++ b/xen/drivers/passthrough/vtd/dmar.c	Tue Jan 22 15:13:43 2013 +0000
@@ -29,6 +29,7 @@
 #include <xen/pci.h>
 #include <xen/pci_regs.h>
 #include <asm/string.h>
+#include <acpi/actables.h>
 #include "dmar.h"
 #include "iommu.h"
 #include "extern.h"
@@ -46,7 +47,6 @@
 static LIST_HEAD_READ_MOSTLY(acpi_atsr_units);
 static LIST_HEAD_READ_MOSTLY(acpi_rhsa_units);
 
-static struct acpi_table_header *__read_mostly dmar_table;
 static int __read_mostly dmar_flags;
 static u64 __read_mostly igd_drhd_address;
 
@@ -821,26 +821,56 @@
 /* SINIT saved in SinitMleData in TXT heap (which is DMA protected) */
 #define parse_dmar_table(h) tboot_parse_dmar_table(h)
 
+static struct acpi_table_header *map_dmar(void)
+{
+    acpi_physical_address addr;
+    u32 sz;
+
+    if (acpi_tb_get_table_physical_location(ACPI_SIG_DMAR, &addr, &sz)) {
+        return NULL;
+    }
+    return (struct acpi_table_header*) ioremap(addr, sz);
+}
+
+static void unmap_dmar(struct acpi_table_header *dmar_table)
+{
+    iounmap(dmar_table);
+}
+
 int __init acpi_dmar_init(void)
 {
-    acpi_get_table(ACPI_SIG_DMAR, 0, &dmar_table);
     return parse_dmar_table(acpi_parse_dmar);
 }
 
 void acpi_dmar_reinstate(void)
 {
-    if ( dmar_table == NULL )
-        return;
-    dmar_table->signature[0] = 'D';
-    dmar_table->checksum += 'X'-'D';
+    unsigned long flags;
+    struct acpi_table_header *dmar_table;
+    /* Disabling IRQs avoids cross-CPU TLB flush in map_pages_to_xen(). */
+    local_irq_save(flags);
+    dmar_table = map_dmar(); /* needs to be dynamically fetched here as acpi_get_table reuses the returned virtual address */
+    if (dmar_table) {
+        dmar_table->signature[0] = 'D';
+        dmar_table->checksum += 'X'-'D';
+        unmap_dmar(dmar_table);
+    }
+    local_irq_restore(flags);
 }
 
 void acpi_dmar_zap(void)
 {
-    if ( dmar_table == NULL )
-        return;
-    dmar_table->signature[0] = 'X';
-    dmar_table->checksum -= 'X'-'D';
+    unsigned long flags;
+    struct acpi_table_header *dmar_table;
+    /* Disabling IRQs avoids cross-CPU TLB flush in map_pages_to_xen(). */
+    local_irq_save(flags);
+    dmar_table = map_dmar();
+    if (dmar_table) {
+        dmar_table->signature[0] = 'X';
+        dmar_table->checksum -= 'X'-'D';
+        unmap_dmar(dmar_table);
+    }
+    local_irq_restore(flags);
+
 }
 
 int platform_supports_intremap(void)
diff -r 4b476378fc35 xen/include/acpi/actables.h
--- a/xen/include/acpi/actables.h	Mon Jan 21 17:03:10 2013 +0000
+++ b/xen/include/acpi/actables.h	Tue Jan 22 15:13:43 2013 +0000
@@ -61,6 +61,8 @@
 		   char *oem_id,
 		   char *oem_table_id, acpi_native_uint * table_index);
 
+acpi_status acpi_tb_get_table_physical_location(char *signature, acpi_physical_address *out_addr, u32 *out_size);
+
 /*
  * tbinstal - Table removal and deletion
  */