Merge remote-tracking branch 'remotes/qmp-unstable/queue/qmp' into staging

* remotes/qmp-unstable/queue/qmp:
  docs: add memory-hotplug.txt
  qemu-options.hx: improve -m description
  virtio-balloon: Add some trace events
  virtio-balloon: Fix balloon not working correctly when hotplug memory
  pc-dimm: add a function to calculate VM's current RAM size

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

docs/memory-hotplug.txt

@@ -0,0 +1,76 @@
+QEMU memory hotplug
+===================
+
+This document explains how to use the memory hotplug feature in QEMU,
+which is present since v2.1.0.
+
+Please, note that memory hotunplug is not supported yet. This means
+that you're able to add memory, but you're not able to remove it.
+Also, proper guest support is required for memory hotplug to work.
+
+Basic RAM hotplug
+-----------------
+
+In order to be able to hotplug memory, QEMU has to be told how many
+hotpluggable memory slots to create and what is the maximum amount of
+memory the guest can grow. This is done at startup time by means of
+the -m command-line option, which has the following format:
+
+ -m [size=]megs[,slots=n,maxmem=size]
+
+Where,
+
+ - "megs" is the startup RAM. It is the RAM the guest will boot with
+ - "slots" is the number of hotpluggable memory slots
+ - "maxmem" is the maximum RAM size the guest can have
+
+For example, the following command-line:
+
+ qemu [...] 1G,slots=3,maxmem=4G
+
+Creates a guest with 1GB of memory and three hotpluggable memory slots.
+The hotpluggable memory slots are empty when the guest is booted, so all
+memory the guest will see after boot is 1GB. The maximum memory the
+guest can reach is 4GB. This means that three additional gigabytes can be
+hotplugged by using any combination of the available memory slots.
+
+Two monitor commands are used to hotplug memory:
+
+ - "object_add": creates a memory backend object
+ - "device_add": creates a front-end pc-dimm device and inserts it
+                 into the first empty slot
+
+For example, the following commands add another 1GB to the guest
+discussed earlier:
+
+  (qemu) object_add memory-backend-ram,id=mem1,size=1G
+  (qemu) device_add pc-dimm,id=dimm1,memdev=mem1
+
+Using the file backend
+----------------------
+
+Besides basic RAM hotplug, QEMU also supports using files as a memory
+backend. This is useful for using hugetlbfs in Linux, which provides
+access to bigger page sizes.
+
+For example, assuming that the host has 1GB hugepages available in
+the /mnt/hugepages-1GB directory, a 1GB hugepage could be hotplugged
+into the guest from the previous section with the following commands:
+
+  (qemu) object_add memory-backend-file,id=mem1,size=1G,mem-path=/mnt/hugepages-1GB
+  (qemu) device_add pc-dimm,id=dimm1,memdev=mem1
+
+It's also possible to start a guest with memory cold-plugged into the
+hotpluggable memory slots. This might seem counterintuitive at first,
+but this allows for a lot of flexibility when using the file backend.
+
+In the following command-line example, a 8GB guest is created where 6GB
+comes from regular RAM, 1GB is a 1GB hugepage page and 256MB is from
+2MB pages. Also, the guest has additional memory slots to hotplug more
+2GB if needed:
+
+ qemu [...] -m 6GB,slots=4,maxmem=10G \
+   -object memory-backend-file,id=mem1,size=1G,mem-path=/mnt/hugepages-1G \
+   -device pc-dimm,id=dimm1,memdev=mem1 \
+   -object memory-backend-file,id=mem2,size=256M,mem-path=/mnt/hugepages-2MB \
+   -device pc-dimm,id=dimm2,memdev=mem2

hw/mem/pc-dimm.c

@@ -100,6 +100,32 @@ int qmp_pc_dimm_device_list(Object *obj, void *opaque)
     return 0;
 }
 
+ram_addr_t get_current_ram_size(void)
+{
+    MemoryDeviceInfoList *info_list = NULL;
+    MemoryDeviceInfoList **prev = &info_list;
+    MemoryDeviceInfoList *info;
+    ram_addr_t size = ram_size;
+
+    qmp_pc_dimm_device_list(qdev_get_machine(), &prev);
+    for (info = info_list; info; info = info->next) {
+        MemoryDeviceInfo *value = info->value;
+
+        if (value) {
+            switch (value->kind) {
+            case MEMORY_DEVICE_INFO_KIND_DIMM:
+                size += value->dimm->size;
+                break;
+            default:
+                break;
+            }
+        }
+    }
+    qapi_free_MemoryDeviceInfoList(info_list);
+
+    return size;
+}
+
 static int pc_dimm_slot2bitmap(Object *obj, void *opaque)
 {
     unsigned long *bitmap = opaque;

hw/virtio/virtio-balloon.c

@@ -25,6 +25,7 @@
 #include "exec/address-spaces.h"
 #include "qapi/visitor.h"
 #include "qapi-event.h"
+#include "trace.h"
 
 #if defined(__linux__)
 #include <sys/mman.h>
@@ -222,6 +223,8 @@ static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
             if (!int128_nz(section.size) || !memory_region_is_ram(section.mr))
                 continue;
 
+            trace_virtio_balloon_handle_output(memory_region_name(section.mr),
+                                               pa);
             /* Using memory_region_get_ram_ptr is bending the rules a bit, but
                should be OK because we only want a single page.  */
             addr = section.offset_within_region;
@@ -285,6 +288,7 @@ static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
     config.num_pages = cpu_to_le32(dev->num_pages);
     config.actual = cpu_to_le32(dev->actual);
 
+    trace_virtio_balloon_get_config(config.num_pages, config.actual);
     memcpy(config_data, &config, sizeof(struct virtio_balloon_config));
 }
 
@@ -294,13 +298,16 @@ static void virtio_balloon_set_config(VirtIODevice *vdev,
     VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
     struct virtio_balloon_config config;
     uint32_t oldactual = dev->actual;
+    ram_addr_t vm_ram_size = get_current_ram_size();
+
     memcpy(&config, config_data, sizeof(struct virtio_balloon_config));
     dev->actual = le32_to_cpu(config.actual);
     if (dev->actual != oldactual) {
-        qapi_event_send_balloon_change(ram_size -
+        qapi_event_send_balloon_change(vm_ram_size -
                         ((ram_addr_t) dev->actual << VIRTIO_BALLOON_PFN_SHIFT),
                         &error_abort);
     }
+    trace_virtio_balloon_set_config(dev->actual, oldactual);
 }
 
 static uint32_t virtio_balloon_get_features(VirtIODevice *vdev, uint32_t f)
@@ -312,22 +319,24 @@ static uint32_t virtio_balloon_get_features(VirtIODevice *vdev, uint32_t f)
 static void virtio_balloon_stat(void *opaque, BalloonInfo *info)
 {
     VirtIOBalloon *dev = opaque;
-    info->actual = ram_size - ((uint64_t) dev->actual <<
+    info->actual = get_current_ram_size() - ((uint64_t) dev->actual <<
-                               VIRTIO_BALLOON_PFN_SHIFT);
+                                             VIRTIO_BALLOON_PFN_SHIFT);
 }
 
 static void virtio_balloon_to_target(void *opaque, ram_addr_t target)
 {
     VirtIOBalloon *dev = VIRTIO_BALLOON(opaque);
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    ram_addr_t vm_ram_size = get_current_ram_size();
 
-    if (target > ram_size) {
+    if (target > vm_ram_size) {
-        target = ram_size;
+        target = vm_ram_size;
     }
     if (target) {
-        dev->num_pages = (ram_size - target) >> VIRTIO_BALLOON_PFN_SHIFT;
+        dev->num_pages = (vm_ram_size - target) >> VIRTIO_BALLOON_PFN_SHIFT;
         virtio_notify_config(vdev);
     }
+    trace_virtio_balloon_to_target(target, dev->num_pages);
 }
 
 static void virtio_balloon_save(QEMUFile *f, void *opaque)

include/exec/cpu-common.h

@@ -52,6 +52,7 @@ typedef uintptr_t ram_addr_t;
 #endif
 
 extern ram_addr_t ram_size;
+ram_addr_t get_current_ram_size(void);
 
 /* memory API */
 

qemu-options.hx

@@ -237,12 +237,24 @@ DEF("m", HAS_ARG, QEMU_OPTION_m,
     "NOTE: Some architectures might enforce a specific granularity\n",
     QEMU_ARCH_ALL)
 STEXI
-@item -m [size=]@var{megs}
+@item -m [size=]@var{megs}[,slots=n,maxmem=size]
 @findex -m
-Set virtual RAM size to @var{megs} megabytes. Default is 128 MiB.  Optionally,
+Sets guest startup RAM size to @var{megs} megabytes. Default is 128 MiB.
-a suffix of ``M'' or ``G'' can be used to signify a value in megabytes or
+Optionally, a suffix of ``M'' or ``G'' can be used to signify a value in
-gigabytes respectively. Optional pair @var{slots}, @var{maxmem} could be used
+megabytes or gigabytes respectively. Optional pair @var{slots}, @var{maxmem}
-to set amount of hotluggable memory slots and possible maximum amount of memory.
+could be used to set amount of hotpluggable memory slots and maximum amount of
+memory. Note that @var{maxmem} must be aligned to the page size.
+
+For example, the following command-line sets the guest startup RAM size to
+1GB, creates 3 slots to hotplug additional memory and sets the maximum
+memory the guest can reach to 4GB:
+
+@example
+qemu-system-x86_64 -m 1G,slots=3,maxmem=4G
+@end example
+
+If @var{slots} and @var{maxmem} are not specified, memory hotplug won't
+be enabled and the guest startup RAM will never increase.
 ETEXI
 
 DEF("mem-path", HAS_ARG, QEMU_OPTION_mempath,

stubs/qmp_pc_dimm_device_list.c

@@ -5,3 +5,8 @@ int qmp_pc_dimm_device_list(Object *obj, void *opaque)
 {
    return 0;
 }
+
+ram_addr_t get_current_ram_size(void)
+{
+    return ram_size;
+}

trace-events

@@ -143,6 +143,10 @@ cpu_out(unsigned int addr, unsigned int val) "addr %#x value %u"
 # balloon.c
 # Since requests are raised via monitor, not many tracepoints are needed.
 balloon_event(void *opaque, unsigned long addr) "opaque %p addr %lu"
+virtio_balloon_handle_output(const char *name, uint64_t gpa) "setion name: %s gpa: %"PRIx64""
+virtio_balloon_get_config(uint32_t num_pages, uint32_t acutal) "num_pages: %d acutal: %d"
+virtio_balloon_set_config(uint32_t acutal, uint32_t oldacutal) "acutal: %d oldacutal: %d"
+virtio_balloon_to_target(uint64_t target, uint32_t num_pages) "balloon target: %"PRIx64" num_pages: %d"
 
 # hw/intc/apic_common.c
 cpu_set_apic_base(uint64_t val) "%016"PRIx64