[Xen-devel] [PATCH 1/2] hvmloader: limit CPUs exposed to guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

Various Linux versions allocate (partial) per-CPU data for all of them,
as there is no indication in MADT whether they're hotpluggable. That's
a little wasteful in terms of resource consumption especially for
- guests with not overly much memory assigned,
- 32-bit guests not having overly much address space available.
Therefore limit what we put into MADT to the "maxvcpus" value, and make
sure AML doesn't touch memory addresses corresponding to CPUs beyond
that value (we can't reasonably make the respective processor objects
disappear).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- 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");

Attachment: hvmloader-limit-CPUs.patch
Description: Text document

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