[RFC PATCH 01/13] machine: Add mirrorvcpus=N suboption to -smp

[Ashish Kalra <Ashish.Kalra@xxxxxxx>]

From: Dov Murik <dovmurik@xxxxxxxxxxxxxxxxxx>

Add a notion of mirror vcpus to CpuTopology, which will allow to
designate a few vcpus (normally 1) for running the guest
migration handler (MH).

Example usage for starting a 4-vcpu guest, of which 1 vcpu is marked as
mirror vcpu.

    qemu-system-x86_64 -smp 4,mirrorvcpus=1 ...

Signed-off-by: Dov Murik <dovmurik@xxxxxxxxxxxxxxxxxx>
Co-developed-by: Ashish Kalra <ashish.kalra@xxxxxxx>
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
---
 hw/core/machine.c   | 7 +++++++
 hw/i386/pc.c        | 7 +++++++
 include/hw/boards.h | 1 +
 qapi/machine.json   | 5 ++++-
 softmmu/vl.c        | 3 +++
 5 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/hw/core/machine.c b/hw/core/machine.c
index 943974d411..059262f914 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -749,6 +749,7 @@ static void smp_parse(MachineState *ms, SMPConfiguration *config, Error **errp)
     unsigned sockets = config->has_sockets ? config->sockets : 0;
     unsigned cores   = config->has_cores ? config->cores : 0;
     unsigned threads = config->has_threads ? config->threads : 0;
+    unsigned mirror_vcpus = config->has_mirrorvcpus ? config->mirrorvcpus : 0;
 
     if (config->has_dies && config->dies != 0 && config->dies != 1) {
         error_setg(errp, "dies not supported by this machine's CPU topology");
@@ -787,6 +788,11 @@ static void smp_parse(MachineState *ms, SMPConfiguration *config, Error **errp)
         return;
     }
 
+    if (mirror_vcpus > ms->smp.max_cpus) {
+        error_setg(errp, "mirror vcpus must be less than max cpus");
+        return;
+    }
+
     if (sockets * cores * threads != ms->smp.max_cpus) {
         error_setg(errp, "Invalid CPU topology: "
                    "sockets (%u) * cores (%u) * threads (%u) "
@@ -800,6 +806,7 @@ static void smp_parse(MachineState *ms, SMPConfiguration *config, Error **errp)
     ms->smp.cores = cores;
     ms->smp.threads = threads;
     ms->smp.sockets = sockets;
+    ms->smp.mirror_vcpus = mirror_vcpus;
 }
 
 static void machine_get_smp(Object *obj, Visitor *v, const char *name,
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index c2b9d62a35..3856a47390 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -719,6 +719,7 @@ static void pc_smp_parse(MachineState *ms, SMPConfiguration *config, Error **err
     unsigned dies    = config->has_dies ? config->dies : 1;
     unsigned cores   = config->has_cores ? config->cores : 0;
     unsigned threads = config->has_threads ? config->threads : 0;
+    unsigned mirror_vcpus = config->has_mirrorvcpus ? config->mirrorvcpus : 0;
 
     /* compute missing values, prefer sockets over cores over threads */
     if (cpus == 0 || sockets == 0) {
@@ -753,6 +754,11 @@ static void pc_smp_parse(MachineState *ms, SMPConfiguration *config, Error **err
         return;
     }
 
+    if (mirror_vcpus > ms->smp.max_cpus) {
+        error_setg(errp, "mirror vcpus must be less than max cpus");
+        return;
+    }
+
     if (sockets * dies * cores * threads != ms->smp.max_cpus) {
         error_setg(errp, "Invalid CPU topology deprecated: "
                    "sockets (%u) * dies (%u) * cores (%u) * threads (%u) "
@@ -767,6 +773,7 @@ static void pc_smp_parse(MachineState *ms, SMPConfiguration *config, Error **err
     ms->smp.threads = threads;
     ms->smp.sockets = sockets;
     ms->smp.dies = dies;
+    ms->smp.mirror_vcpus = mirror_vcpus;
 }
 
 static
diff --git a/include/hw/boards.h b/include/hw/boards.h
index accd6eff35..b0e599096a 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -286,6 +286,7 @@ typedef struct CpuTopology {
     unsigned int threads;
     unsigned int sockets;
     unsigned int max_cpus;
+    unsigned int mirror_vcpus;
 } CpuTopology;
 
 /**
diff --git a/qapi/machine.json b/qapi/machine.json
index c3210ee1fb..7888601715 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -1303,6 +1303,8 @@
 #
 # @maxcpus: maximum number of hotpluggable virtual CPUs in the virtual machine
 #
+# @mirrorvcpus: maximum number of mirror virtual CPUs in the virtual machine
+#
 # Since: 6.1
 ##
 { 'struct': 'SMPConfiguration', 'data': {
@@ -1311,4 +1313,5 @@
      '*dies': 'int',
      '*cores': 'int',
      '*threads': 'int',
-     '*maxcpus': 'int' } }
+     '*maxcpus': 'int',
+     '*mirrorvcpus': 'int' } }
diff --git a/softmmu/vl.c b/softmmu/vl.c
index 5ca11e7469..6261f1cfb1 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -710,6 +710,9 @@ static QemuOptsList qemu_smp_opts = {
         }, {
             .name = "maxcpus",
             .type = QEMU_OPT_NUMBER,
+        }, {
+            .name = "mirrorvcpus",
+            .type = QEMU_OPT_NUMBER,
         },
         { /*End of list */ }
     },
-- 
2.17.1