[Qemu-devel] [PATCH] hw: add .min_cpus and .default_cpus fields to machine_class

["Emilio G. Cota" <cota@braap.org>]

max_cpus needs to be an upper bound on the number of vCPUs
initialized; otherwise TCG region initialization breaks.

Some boards initialize a hard-coded number of vCPUs, which is not
captured by the global max_cpus. Fix it by adding the .min_cpus
field to machine_class.

This commit also changes some user-facing behaviour: we now die if
-smp is below this hard-coded vCPU minimum instead of silently
ignoring the passed -smp value (sometimes announcing this by printing
a warning). However, the introduction of .default_cpus lessens the
likelihood that users will notice this: if -smp isn't set, we now
assign the value in .default_cpus to both smp_cpus and max_cpus. IOW,
if a user does not set -smp, they always get a correct number of vCPUs.

This change fixes 3468b59 ("tcg: enable multiple TCG contexts in
softmmu", 2017-10-24), which broke TCG initialization for some
ARM boards.

Fixes: 3468b59e18b179bc63c7ce934de912dfa9596122
Reported-by: Thomas Huth <thuth@redhat.com>
Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
---
 hw/arm/exynos4_boards.c | 12 ++++--------
 hw/arm/raspi.c          |  2 ++
 hw/arm/xlnx-zcu102.c    |  5 +++++
 include/hw/boards.h     |  5 +++++
 vl.c                    | 28 +++++++++++++++++++++++++---
 5 files changed, 41 insertions(+), 11 deletions(-)

diff --git a/hw/arm/exynos4_boards.c b/hw/arm/exynos4_boards.c
index f1441ec..750162c 100644
--- a/hw/arm/exynos4_boards.c
+++ b/hw/arm/exynos4_boards.c
@@ -27,7 +27,6 @@
 #include "qemu-common.h"
 #include "cpu.h"
 #include "sysemu/sysemu.h"
-#include "sysemu/qtest.h"
 #include "hw/sysbus.h"
 #include "net/net.h"
 #include "hw/arm/arm.h"
@@ -129,13 +128,6 @@ exynos4_boards_init_common(MachineState *machine,
                            Exynos4BoardType board_type)
 {
     Exynos4BoardState *s = g_new(Exynos4BoardState, 1);
-    MachineClass *mc = MACHINE_GET_CLASS(machine);
-
-    if (smp_cpus != EXYNOS4210_NCPUS && !qtest_enabled()) {
-        error_report("%s board supports only %d CPU cores, ignoring smp_cpus"
-                     " value",
-                     mc->name, EXYNOS4210_NCPUS);
-    }
 
     exynos4_board_binfo.ram_size = exynos4_board_ram_size[board_type];
     exynos4_board_binfo.board_id = exynos4_board_id[board_type];
@@ -189,6 +181,8 @@ static void nuri_class_init(ObjectClass *oc, void *data)
     mc->desc = "Samsung NURI board (Exynos4210)";
     mc->init = nuri_init;
     mc->max_cpus = EXYNOS4210_NCPUS;
+    mc->min_cpus = EXYNOS4210_NCPUS;
+    mc->default_cpus = EXYNOS4210_NCPUS;
     mc->ignore_memory_transaction_failures = true;
 }
 
@@ -205,6 +199,8 @@ static void smdkc210_class_init(ObjectClass *oc, void *data)
     mc->desc = "Samsung SMDKC210 board (Exynos4210)";
     mc->init = smdkc210_init;
     mc->max_cpus = EXYNOS4210_NCPUS;
+    mc->min_cpus = EXYNOS4210_NCPUS;
+    mc->default_cpus = EXYNOS4210_NCPUS;
     mc->ignore_memory_transaction_failures = true;
 }
 
diff --git a/hw/arm/raspi.c b/hw/arm/raspi.c
index 5941c9f..cd5fa8c 100644
--- a/hw/arm/raspi.c
+++ b/hw/arm/raspi.c
@@ -167,6 +167,8 @@ static void raspi2_machine_init(MachineClass *mc)
     mc->no_floppy = 1;
     mc->no_cdrom = 1;
     mc->max_cpus = BCM2836_NCPUS;
+    mc->min_cpus = BCM2836_NCPUS;
+    mc->default_cpus = BCM2836_NCPUS;
     mc->default_ram_size = 1024 * 1024 * 1024;
     mc->ignore_memory_transaction_failures = true;
 };
diff --git a/hw/arm/xlnx-zcu102.c b/hw/arm/xlnx-zcu102.c
index e2d15a1..395d1b5 100644
--- a/hw/arm/xlnx-zcu102.c
+++ b/hw/arm/xlnx-zcu102.c
@@ -185,6 +185,9 @@ static void xlnx_ep108_machine_class_init(ObjectClass *oc, void *data)
     mc->block_default_type = IF_IDE;
     mc->units_per_default_bus = 1;
     mc->ignore_memory_transaction_failures = true;
+    mc->max_cpus = XLNX_ZYNQMP_NUM_APU_CPUS + XLNX_ZYNQMP_NUM_RPU_CPUS;
+    mc->min_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
+    mc->default_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
 }
 
 static const TypeInfo xlnx_ep108_machine_init_typeinfo = {
@@ -241,6 +244,8 @@ static void xlnx_zcu102_machine_class_init(ObjectClass *oc, void *data)
     mc->units_per_default_bus = 1;
     mc->ignore_memory_transaction_failures = true;
     mc->max_cpus = XLNX_ZYNQMP_NUM_APU_CPUS + XLNX_ZYNQMP_NUM_RPU_CPUS;
+    mc->min_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
+    mc->default_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
 }
 
 static const TypeInfo xlnx_zcu102_machine_init_typeinfo = {
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 191a5b3..62f160e 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -102,6 +102,9 @@ typedef struct {
 
 /**
  * MachineClass:
+ * @max_cpus: maximum number of CPUs supported. Default: 1
+ * @min_cpus: minimum number of CPUs supported. Default: 1
+ * @default_cpus: number of CPUs instantiated if none are specified. Default: 1
  * @get_hotplug_handler: this function is called during bus-less
  *    device hotplug. If defined it returns pointer to an instance
  *    of HotplugHandler object, which handles hotplug operation
@@ -167,6 +170,8 @@ struct MachineClass {
     BlockInterfaceType block_default_type;
     int units_per_default_bus;
     int max_cpus;
+    int min_cpus;
+    int default_cpus;
     unsigned int no_serial:1,
         no_parallel:1,
         use_virtcon:1,
diff --git a/vl.c b/vl.c
index ec29909..3ca5ee8 100644
--- a/vl.c
+++ b/vl.c
@@ -160,8 +160,8 @@ Chardev *virtcon_hds[MAX_VIRTIO_CONSOLES];
 Chardev *sclp_hds[MAX_SCLP_CONSOLES];
 int win2k_install_hack = 0;
 int singlestep = 0;
-int smp_cpus = 1;
-unsigned int max_cpus = 1;
+int smp_cpus;
+unsigned int max_cpus;
 int smp_cores = 1;
 int smp_threads = 1;
 int acpi_enabled = 1;
@@ -4330,12 +4330,34 @@ int main(int argc, char **argv, char **envp)
     smp_parse(qemu_opts_find(qemu_find_opts("smp-opts"), NULL));
 
     machine_class->max_cpus = machine_class->max_cpus ?: 1; /* Default to UP */
+    machine_class->min_cpus = machine_class->min_cpus ?: 1;
+    machine_class->default_cpus = machine_class->default_cpus ?: 1;
+
+    /* if -smp is not set, default to mc->default_cpus */
+    if (!smp_cpus) {
+        smp_cpus = machine_class->default_cpus;
+        max_cpus = machine_class->default_cpus;
+    }
+
+    /* sanity-check smp_cpus and max_cpus */
+    if (smp_cpus < machine_class->min_cpus) {
+        error_report("Invalid SMP CPUs %d. The min CPUs "
+                     "supported by machine '%s' is %d", smp_cpus,
+                     machine_class->name, machine_class->min_cpus);
+        exit(1);
+    }
     if (max_cpus > machine_class->max_cpus) {
-        error_report("Invalid SMP CPUs %d. The max CPUs "
+        error_report("Invalid max SMP CPUs %d. The max CPUs "
                      "supported by machine '%s' is %d", max_cpus,
                      machine_class->name, machine_class->max_cpus);
         exit(1);
     }
+    if (max_cpus < machine_class->min_cpus) {
+        error_report("Invalid max SMP CPUs %d. The min CPUs "
+                     "supported by machine '%s' is %d", max_cpus,
+                     machine_class->name, machine_class->min_cpus);
+        exit(1);
+    }
 
     /*
      * Get the default machine options from the machine if it is not already
-- 
2.7.4