--- a/tools/firmware/hvmloader/acpi/build.c
+++ b/tools/firmware/hvmloader/acpi/build.c
@@ -48,6 +48,7 @@ struct acpi_info {
     uint8_t  com2_present:1;    /* 0[1] - System has COM2? */
     uint8_t  lpt1_present:1;    /* 0[2] - System has LPT1? */
     uint8_t  hpet_present:1;    /* 0[3] - System has HPET? */
+    uint16_t nr_cpus;           /* 2    - Number of CPUs */
     uint32_t pci_min, pci_len;  /* 4, 8 - PCI I/O hole boundaries */
     uint32_t madt_csum_addr;    /* 12   - Address of MADT checksum */
     uint32_t madt_lapic0_addr;  /* 16   - Address of first MADT LAPIC struct */
@@ -55,9 +56,6 @@ struct acpi_info {
     uint64_t pci_hi_min, pci_hi_len; /* 24, 32 - PCI I/O hole boundaries */
 };
 
-/* Number of processor objects in the chosen DSDT. */
-static unsigned int nr_processor_objects;
-
 static void set_checksum(
     void *table, uint32_t checksum_offset, uint32_t length)
 {
@@ -89,7 +87,7 @@ static struct acpi_20_madt *construct_ma
     sz  = sizeof(struct acpi_20_madt);
     sz += sizeof(struct acpi_20_madt_intsrcovr) * 16;
     sz += sizeof(struct acpi_20_madt_ioapic);
-    sz += sizeof(struct acpi_20_madt_lapic) * nr_processor_objects;
+    sz += sizeof(struct acpi_20_madt_lapic) * hvm_info->nr_vcpus;
 
     madt = mem_alloc(sz, 16);
     if (!madt) return NULL;
@@ -142,8 +140,9 @@ static struct acpi_20_madt *construct_ma
     io_apic->ioapic_addr = IOAPIC_BASE_ADDRESS;
 
     lapic = (struct acpi_20_madt_lapic *)(io_apic + 1);
+    info->nr_cpus = hvm_info->nr_vcpus;
     info->madt_lapic0_addr = (uint32_t)lapic;
-    for ( i = 0; i < nr_processor_objects; i++ )
+    for ( i = 0; i < hvm_info->nr_vcpus; i++ )
     {
         memset(lapic, 0, sizeof(*lapic));
         lapic->type    = ACPI_PROCESSOR_LOCAL_APIC;
@@ -151,8 +150,7 @@ static struct acpi_20_madt *construct_ma
         /* Processor ID must match processor-object IDs in the DSDT. */
         lapic->acpi_processor_id = i;
         lapic->apic_id = LAPIC_ID(i);
-        lapic->flags = ((i < hvm_info->nr_vcpus) &&
-                        test_bit(i, hvm_info->vcpu_online)
+        lapic->flags = (test_bit(i, hvm_info->vcpu_online)
                         ? ACPI_LOCAL_APIC_ENABLED : 0);
         lapic++;
     }
@@ -534,14 +532,12 @@ void acpi_build_tables(struct acpi_confi
         dsdt = mem_alloc(config->dsdt_15cpu_len, 16);
         if (!dsdt) goto oom;
         memcpy(dsdt, config->dsdt_15cpu, config->dsdt_15cpu_len);
-        nr_processor_objects = 15;
     }
     else
     {
         dsdt = mem_alloc(config->dsdt_anycpu_len, 16);
         if (!dsdt) goto oom;
         memcpy(dsdt, config->dsdt_anycpu, config->dsdt_anycpu_len);
-        nr_processor_objects = HVM_MAX_VCPUS;
     }
 
     /*
--- a/tools/firmware/hvmloader/acpi/dsdt.asl
+++ b/tools/firmware/hvmloader/acpi/dsdt.asl
@@ -50,7 +50,8 @@ DefinitionBlock ("DSDT.aml", "DSDT", 2,
            UAR2, 1,
            LTP1, 1,
            HPET, 1,
-           Offset(4),
+           Offset(2),
+           NCPU, 16,
            PMIN, 32,
            PLEN, 32,
            MSUA, 32, /* MADT checksum address */
--- a/tools/firmware/hvmloader/acpi/mk_dsdt.c
+++ b/tools/firmware/hvmloader/acpi/mk_dsdt.c
@@ -150,6 +150,14 @@ int main(int argc, char **argv)
     indent(); printf("MSU, 8\n");
     pop_block();
 
+    /* Processor object helpers. */
+    push_block("Method", "PMAT, 2");
+    push_block("If", "LLess(Arg0, NCPU)");
+    stmt("Return", "ToBuffer(Arg1)");
+    pop_block();
+    stmt("Return", "Buffer() {0, 8, 0xff, 0xff, 0, 0, 0, 0}");
+    pop_block();
+
     /* Define processor objects and control methods. */
     for ( cpu = 0; cpu < max_cpus; cpu++)
     {
@@ -171,17 +179,22 @@ int main(int argc, char **argv)
         pop_block();
 
         push_block("Method", "_MAT, 0");
-        stmt("Return", "ToBuffer(MAT)");
+        if ( cpu )
+            stmt("Return", "PMAT (%d, MAT)", cpu);
+        else
+            stmt("Return", "ToBuffer(MAT)");
         pop_block();
 
         push_block("Method", "_STA");
+        if ( cpu )
+            push_block("If", "LLess(%d, \\_SB.NCPU)", cpu);
         push_block("If", "FLG");
         stmt("Return", "0xF");
         pop_block();
-        push_block("Else", NULL);
+        if ( cpu )
+            pop_block();
         stmt("Return", "0x0");
         pop_block();
-        pop_block();
 
         push_block("Method", "_EJ0, 1, NotSerialized");
         stmt("Sleep", "0xC8");
