[patch] qemu-kvm introduce -maxcpus argument

[Jes Sorensen <jes.sorensen@gmail.com>]

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Hi,

This one introduces a -maxcpus setting, allowing the user to specify
the maximum number of vCPUs the system can have, as discussed with Gleb
earlier in the week.

Cheers,
Jes


[-- Attachment #2: 0002-qemu-kvm-cfg-maxcpus.patch --]
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Introduce -maxcpus flag to QEMU and pass the value to the BIOS through
FW_CFG.

Follow on patch will use it to determine the size of the MADT.

Signed-off-by: Jes Sorensen <jes@sgi.com>

---
 hw/fw_cfg.c          |    1 +
 hw/fw_cfg.h          |    1 +
 kvm/bios/rombios32.c |   16 ++++++++++++++++
 qemu-options.hx      |    9 +++++++++
 sysemu.h             |    1 +
 vl.c                 |    8 ++++++++
 6 files changed, 36 insertions(+)

Index: qemu-kvm/hw/fw_cfg.c
===================================================================
--- qemu-kvm.orig/hw/fw_cfg.c
+++ qemu-kvm/hw/fw_cfg.c
@@ -279,6 +279,7 @@ void *fw_cfg_init(uint32_t ctl_port, uin
     fw_cfg_add_bytes(s, FW_CFG_UUID, qemu_uuid, 16);
     fw_cfg_add_i16(s, FW_CFG_NOGRAPHIC, (uint16_t)(display_type == DT_NOGRAPHIC));
     fw_cfg_add_i16(s, FW_CFG_NB_CPUS, (uint16_t)smp_cpus);
+    fw_cfg_add_i16(s, FW_CFG_MAX_CPUS, (uint16_t)max_cpus);
 
     register_savevm("fw_cfg", -1, 1, fw_cfg_save, fw_cfg_load, s);
     qemu_register_reset(fw_cfg_reset, 0, s);
Index: qemu-kvm/hw/fw_cfg.h
===================================================================
--- qemu-kvm.orig/hw/fw_cfg.h
+++ qemu-kvm/hw/fw_cfg.h
@@ -15,6 +15,7 @@
 #define FW_CFG_INITRD_SIZE      0x0b
 #define FW_CFG_BOOT_DEVICE      0x0c
 #define FW_CFG_NUMA             0x0d
+#define FW_CFG_MAX_CPUS         0x0e
 #define FW_CFG_MAX_ENTRY        0x10
 
 #define FW_CFG_WRITE_CHANNEL    0x4000
Index: qemu-kvm/kvm/bios/rombios32.c
===================================================================
--- qemu-kvm.orig/kvm/bios/rombios32.c
+++ qemu-kvm/kvm/bios/rombios32.c
@@ -441,6 +441,7 @@ void delay_ms(int n)
 }
 
 uint16_t smp_cpus;
+uint16_t max_cpus = MAX_CPUS;
 uint32_t cpuid_signature;
 uint32_t cpuid_features;
 uint32_t cpuid_ext_features;
@@ -484,6 +485,7 @@ void wrmsr_smp(uint32_t index, uint64_t 
 #define QEMU_CFG_ID         0x01
 #define QEMU_CFG_UUID       0x02
 #define QEMU_CFG_NUMA       0x0D
+#define QEMU_CFG_MAX_CPUS   0x0E
 #define QEMU_CFG_ARCH_LOCAL     0x8000
 #define QEMU_CFG_ACPI_TABLES  (QEMU_CFG_ARCH_LOCAL + 0)
 #define QEMU_CFG_SMBIOS_ENTRIES  (QEMU_CFG_ARCH_LOCAL + 1)
@@ -546,6 +548,19 @@ static uint16_t smbios_entries(void)
     return cnt;
 }
 
+static uint16_t get_max_cpus(void)
+{
+    uint16_t cnt;
+
+    qemu_cfg_select(QEMU_CFG_MAX_CPUS);
+    qemu_cfg_read((uint8_t*)&cnt, sizeof(cnt));
+
+    if (!cnt)
+        cnt = MAX_CPUS;
+
+    return cnt;
+}
+
 uint64_t qemu_cfg_get64 (void)
 {
     uint64_t ret;
@@ -1655,6 +1670,7 @@ void acpi_bios_init(void)
     addr += sizeof(SSDTCode);
 
 #ifdef BX_QEMU
+    max_cpus = get_max_cpus();
     qemu_cfg_select(QEMU_CFG_NUMA);
     nb_numa_nodes = qemu_cfg_get64();
 #else
Index: qemu-kvm/qemu-options.hx
===================================================================
--- qemu-kvm.orig/qemu-options.hx
+++ qemu-kvm/qemu-options.hx
@@ -47,6 +47,15 @@ CPUs are supported. On Sparc32 target, L
 to 4.
 ETEXI
 
+DEF("maxcpus", HAS_ARG, QEMU_OPTION_maxcpus,
+    "-maxcpus n      set maximumthe number of possibly CPUs to 'n'\n")
+STEXI
+@item -maxcpus @var{n}
+Set the maximum number of possible CPUs to @var(n). @var(n) has to be
+bigger or equal to the value of -smp. If @var(n) is equal to -smp,
+there will be no space for hotplug cpus to be added later.
+ETEXI
+
 DEF("numa", HAS_ARG, QEMU_OPTION_numa,
     "-numa node[,mem=size][,cpus=cpu[-cpu]][,nodeid=node]\n")
 STEXI
Index: qemu-kvm/sysemu.h
===================================================================
--- qemu-kvm.orig/sysemu.h
+++ qemu-kvm/sysemu.h
@@ -119,6 +119,7 @@ extern int alt_grab;
 extern int usb_enabled;
 extern int no_virtio_balloon;
 extern int smp_cpus;
+extern int max_cpus;
 extern int cursor_hide;
 extern int graphic_rotate;
 extern int no_quit;
Index: qemu-kvm/vl.c
===================================================================
--- qemu-kvm.orig/vl.c
+++ qemu-kvm/vl.c
@@ -246,6 +246,7 @@ int singlestep = 0;
 const char *assigned_devices[MAX_DEV_ASSIGN_CMDLINE];
 int assigned_devices_index;
 int smp_cpus = 1;
+int max_cpus = 16;
 const char *vnc_display;
 int acpi_enabled = 1;
 int no_hpet = 0;
@@ -5666,6 +5667,13 @@ int main(int argc, char **argv, char **e
                     exit(1);
                 }
                 break;
+            case QEMU_OPTION_maxcpus:
+                max_cpus = atoi(optarg);
+                if ((max_cpus < 1) || (max_cpus > machine->max_cpus)) {
+                    fprintf(stderr, "Invalid number of CPUs\n");
+                    exit(1);
+                }
+                break;
 	    case QEMU_OPTION_vnc:
                 display_type = DT_VNC;
 		vnc_display = optarg;