virtio-balloon: add support for page poison reporting and free page reporting

From: Alexander Duyck <[email protected]>

In an upcoming patch a feature named Free Page Reporting is about to be added. In order to avoid any confusion we should drop the use of the word 'report' when referring to Free Page Hinting. So what this patch does is go through and replace all instances of 'report' with 'hint" when we are referring to free page hinting.

Acked-by David Hildenbrand <[email protected]>

Signed-off-by Alexander Duyck <[email protected]>

---
 hw/virtio/virtio-balloon.c         |   74 ++++++++++++++++++------------------
 include/hw/virtio/virtio-balloon.h |   20 +++++-----
 2 files changed, 47 insertions(+), 47 deletions(-)

hw/virtio/virtio-balloon.c +37 -37

index a4729f7fc930..a1d6fb52c876 100644
@@ -466,21 +466,21 @@ static bool get_free_page_hints(VirtIOBalloon *dev)
             ret = false;
             goto out;
         }
-        if (id == dev->free_page_report_cmd_id) {
-            dev->free_page_report_status = FREE_PAGE_REPORT_S_START;
+        if (id == dev->free_page_hint_cmd_id) {
+            dev->free_page_hint_status = FREE_PAGE_HINT_S_START;
         } else {
             /*
              * Stop the optimization only when it has started. This
              * avoids a stale stop sign for the previous command.
              */
-            if (dev->free_page_report_status == FREE_PAGE_REPORT_S_START) {
-                dev->free_page_report_status = FREE_PAGE_REPORT_S_STOP;
+            if (dev->free_page_hint_status == FREE_PAGE_HINT_S_START) {
+                dev->free_page_hint_status = FREE_PAGE_HINT_S_STOP;
             }
         }
     }
 
     if (elem->in_num) {
-        if (dev->free_page_report_status == FREE_PAGE_REPORT_S_START) {
+        if (dev->free_page_hint_status == FREE_PAGE_HINT_S_START) {
             qemu_guest_free_page_hint(elem->in_sg[0].iov_base,
                                       elem->in_sg[0].iov_len);
         }

@@ -506,11 +506,11 @@ static void virtio_ballloon_get_free_page_hints(void *opaque)
         qemu_mutex_unlock(&dev->free_page_lock);
         virtio_notify(vdev, vq);
       /*
-       * Start to poll the vq once the reporting started. Otherwise, continue
+       * Start to poll the vq once the hinting started. Otherwise, continue
        * only when there are entries on the vq, which need to be given back.
        */
     } while (continue_to_get_hints ||
-             dev->free_page_report_status == FREE_PAGE_REPORT_S_START);
+             dev->free_page_hint_status == FREE_PAGE_HINT_S_START);
     virtio_queue_set_notification(vq, 1);
 }
 

@@ -531,14 +531,14 @@ static void virtio_balloon_free_page_start(VirtIOBalloon *s)
         return;
     }
 
-    if (s->free_page_report_cmd_id == UINT_MAX) {
-        s->free_page_report_cmd_id =
-                       VIRTIO_BALLOON_FREE_PAGE_REPORT_CMD_ID_MIN;
+    if (s->free_page_hint_cmd_id == UINT_MAX) {
+        s->free_page_hint_cmd_id =
+                       VIRTIO_BALLOON_FREE_PAGE_HINT_CMD_ID_MIN;
     } else {
-        s->free_page_report_cmd_id++;
+        s->free_page_hint_cmd_id++;
     }
 
-    s->free_page_report_status = FREE_PAGE_REPORT_S_REQUESTED;
+    s->free_page_hint_status = FREE_PAGE_HINT_S_REQUESTED;
     virtio_notify_config(vdev);
 }
 

@@ -546,18 +546,18 @@ static void virtio_balloon_free_page_stop(VirtIOBalloon *s)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(s);
 
-    if (s->free_page_report_status != FREE_PAGE_REPORT_S_STOP) {
+    if (s->free_page_hint_status != FREE_PAGE_HINT_S_STOP) {
         /*
          * The lock also guarantees us that the
          * virtio_ballloon_get_free_page_hints exits after the
-         * free_page_report_status is set to S_STOP.
+         * free_page_hint_status is set to S_STOP.
          */
         qemu_mutex_lock(&s->free_page_lock);
         /*
          * The guest hasn't done the reporting, so host sends a notification
          * to the guest to actively stop the reporting.
          */
-        s->free_page_report_status = FREE_PAGE_REPORT_S_STOP;
+        s->free_page_hint_status = FREE_PAGE_HINT_S_STOP;
         qemu_mutex_unlock(&s->free_page_lock);
         virtio_notify_config(vdev);
     }

@@ -567,15 +567,15 @@ static void virtio_balloon_free_page_done(VirtIOBalloon *s)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(s);
 
-    s->free_page_report_status = FREE_PAGE_REPORT_S_DONE;
+    s->free_page_hint_status = FREE_PAGE_HINT_S_DONE;
     virtio_notify_config(vdev);
 }
 
 static int
-virtio_balloon_free_page_report_notify(NotifierWithReturn *n, void *data)
+virtio_balloon_free_page_hint_notify(NotifierWithReturn *n, void *data)
 {
     VirtIOBalloon *dev = container_of(n, VirtIOBalloon,
-                                      free_page_report_notify);
+                                      free_page_hint_notify);
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     PrecopyNotifyData *pnd = data;
 

@@ -624,7 +624,7 @@ static size_t virtio_balloon_config_size(VirtIOBalloon *s)
     if (virtio_has_feature(features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
         return offsetof(struct virtio_balloon_config, poison_val);
     }
-    return offsetof(struct virtio_balloon_config, free_page_report_cmd_id);
+    return offsetof(struct virtio_balloon_config, free_page_hint_cmd_id);
 }
 
 static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)

@@ -635,14 +635,14 @@ 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);
 
-    if (dev->free_page_report_status == FREE_PAGE_REPORT_S_REQUESTED) {
-        config.free_page_report_cmd_id =
-                       cpu_to_le32(dev->free_page_report_cmd_id);
-    } else if (dev->free_page_report_status == FREE_PAGE_REPORT_S_STOP) {
-        config.free_page_report_cmd_id =
+    if (dev->free_page_hint_status == FREE_PAGE_HINT_S_REQUESTED) {
+        config.free_page_hint_cmd_id =
+                       cpu_to_le32(dev->free_page_hint_cmd_id);
+    } else if (dev->free_page_hint_status == FREE_PAGE_HINT_S_STOP) {
+        config.free_page_hint_cmd_id =
                        cpu_to_le32(VIRTIO_BALLOON_CMD_ID_STOP);
-    } else if (dev->free_page_report_status == FREE_PAGE_REPORT_S_DONE) {
-        config.free_page_report_cmd_id =
+    } else if (dev->free_page_hint_status == FREE_PAGE_HINT_S_DONE) {
+        config.free_page_hint_cmd_id =
                        cpu_to_le32(VIRTIO_BALLOON_CMD_ID_DONE);
     }
 

@@ -743,14 +743,14 @@ static int virtio_balloon_post_load_device(void *opaque, int version_id)
     return 0;
 }
 
-static const VMStateDescription vmstate_virtio_balloon_free_page_report = {
+static const VMStateDescription vmstate_virtio_balloon_free_page_hint = {
     .name = "virtio-balloon-device/free-page-report",
     .version_id = 1,
     .minimum_version_id = 1,
     .needed = virtio_balloon_free_page_support,
     .fields = (VMStateField[]) {
-        VMSTATE_UINT32(free_page_report_cmd_id, VirtIOBalloon),
-        VMSTATE_UINT32(free_page_report_status, VirtIOBalloon),
+        VMSTATE_UINT32(free_page_hint_cmd_id, VirtIOBalloon),
+        VMSTATE_UINT32(free_page_hint_status, VirtIOBalloon),
         VMSTATE_END_OF_LIST()
     }
 };

@@ -766,7 +766,7 @@ static const VMStateDescription vmstate_virtio_balloon_device = {
         VMSTATE_END_OF_LIST()
     },
     .subsections = (const VMStateDescription * []) {
-        &vmstate_virtio_balloon_free_page_report,
+        &vmstate_virtio_balloon_free_page_hint,
         NULL
     }
 };

@@ -797,12 +797,12 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
                            VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
         s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE,
                                            virtio_balloon_handle_free_page_vq);
-        s->free_page_report_status = FREE_PAGE_REPORT_S_STOP;
-        s->free_page_report_cmd_id =
-                           VIRTIO_BALLOON_FREE_PAGE_REPORT_CMD_ID_MIN;
-        s->free_page_report_notify.notify =
-                                       virtio_balloon_free_page_report_notify;
-        precopy_add_notifier(&s->free_page_report_notify);
+        s->free_page_hint_status = FREE_PAGE_HINT_S_STOP;
+        s->free_page_hint_cmd_id =
+                           VIRTIO_BALLOON_FREE_PAGE_HINT_CMD_ID_MIN;
+        s->free_page_hint_notify.notify =
+                                       virtio_balloon_free_page_hint_notify;
+        precopy_add_notifier(&s->free_page_hint_notify);
         if (s->iothread) {
             object_ref(OBJECT(s->iothread));
             s->free_page_bh = aio_bh_new(iothread_get_aio_context(s->iothread),

@@ -827,7 +827,7 @@ static void virtio_balloon_device_unrealize(DeviceState *dev, Error **errp)
     if (virtio_balloon_free_page_support(s)) {
         qemu_bh_delete(s->free_page_bh);
         virtio_balloon_free_page_stop(s);
-        precopy_remove_notifier(&s->free_page_report_notify);
+        precopy_remove_notifier(&s->free_page_hint_notify);
     }
     balloon_stats_destroy_timer(s);
     qemu_remove_balloon_handler(s);

include/hw/virtio/virtio-balloon.h +9 -9

index d1c968d2376e..108cff97e71a 100644
@@ -23,7 +23,7 @@
 #define VIRTIO_BALLOON(obj) \
         OBJECT_CHECK(VirtIOBalloon, (obj), TYPE_VIRTIO_BALLOON)
 
-#define VIRTIO_BALLOON_FREE_PAGE_REPORT_CMD_ID_MIN 0x80000000
+#define VIRTIO_BALLOON_FREE_PAGE_HINT_CMD_ID_MIN 0x80000000
 
 typedef struct virtio_balloon_stat VirtIOBalloonStat;
 

@@ -33,20 +33,20 @@ typedef struct virtio_balloon_stat_modern {
        uint64_t val;
 } VirtIOBalloonStatModern;
 
-enum virtio_balloon_free_page_report_status {
-    FREE_PAGE_REPORT_S_STOP = 0,
-    FREE_PAGE_REPORT_S_REQUESTED = 1,
-    FREE_PAGE_REPORT_S_START = 2,
-    FREE_PAGE_REPORT_S_DONE = 3,
+enum virtio_balloon_free_page_hint_status {
+    FREE_PAGE_HINT_S_STOP = 0,
+    FREE_PAGE_HINT_S_REQUESTED = 1,
+    FREE_PAGE_HINT_S_START = 2,
+    FREE_PAGE_HINT_S_DONE = 3,
 };
 
 typedef struct VirtIOBalloon {
     VirtIODevice parent_obj;
     VirtQueue *ivq, *dvq, *svq, *free_page_vq;
-    uint32_t free_page_report_status;
+    uint32_t free_page_hint_status;
     uint32_t num_pages;
     uint32_t actual;
-    uint32_t free_page_report_cmd_id;
+    uint32_t free_page_hint_cmd_id;
     uint64_t stats[VIRTIO_BALLOON_S_NR];
     VirtQueueElement *stats_vq_elem;
     size_t stats_vq_offset;

@@ -55,7 +55,7 @@ typedef struct VirtIOBalloon {
     QEMUBH *free_page_bh;
     /*
      * Lock to synchronize threads to access the free page reporting related
-     * fields (e.g. free_page_report_status).
+     * fields (e.g. free_page_hint_status).
      */
     QemuMutex free_page_lock;
     QemuCond  free_page_cond;

There is only one wrong comment remaining I think. Something like

hw/virtio/virtio-balloon.c +0 -0

index a1d6fb52c8..1b2127c04c 100644

Quoted 3 lines · David Hildenbrand

There is only one wrong comment remaining I think. Something like

hw/virtio/virtio-balloon.c static void virtio_balloon_free_page_stop(VirtIOBalloon *s) · line 558

Quoted 12 lines

hw/virtio/virtio-balloon.c +2 -2

index a1d6fb52c8..1b2127c04c 100644
@@ -554,8 +554,8 @@ static void virtio_balloon_free_page_stop(VirtIOBalloon *s)
          */
         qemu_mutex_lock(&s->free_page_lock);
         /*
-         * The guest hasn't done the reporting, so host sends a notification
-         * to the guest to actively stop the reporting.
+         * The guest isn't done with hinting, so the host sends a notification
+         * to the guest to actively stop the hinting.

I'll probably tweak it slightly and drop the "with". So the comment will read:
/*
* The guest isn't done hinting, so host sends a notification

* to the guest to actively stop the hinting. */

There is one other spot left which is support for migration. The name for the VMStateDescription is "virtio-balloon-device/free-page-report". I am assuming I cannot rename that. Otherwise all other references to report on the balloon interface refer to reporting errors from what I can tell.

Quoted 4 lines · Alexander Duyck

Quoted 3 lines · David Hildenbrand

There is only one wrong comment remaining I think. Something like

Quoted 16 lines

hw/virtio/virtio-balloon.c static void virtio_balloon_free_page_stop(VirtIOBalloon *s) · line 558

Quoted 12 lines

hw/virtio/virtio-balloon.c +2 -2

index a1d6fb52c8..1b2127c04c 100644
@@ -554,8 +554,8 @@ static void virtio_balloon_free_page_stop(VirtIOBalloon *s)
          */
         qemu_mutex_lock(&s->free_page_lock);
         /*
-         * The guest hasn't done the reporting, so host sends a notification
-         * to the guest to actively stop the reporting.
+         * The guest isn't done with hinting, so the host sends a notification
+         * to the guest to actively stop the hinting.

I'll probably tweak it slightly and drop the "with". So the comment will read:
/*
* The guest isn't done hinting, so host sends a notification

I always feel like "so host sends" sounds wrong ("the host"). But I am not a native speaker.

Quoted 23 lines · David Hildenbrand

Quoted 4 lines · Alexander Duyck

Quoted 3 lines · David Hildenbrand

There is only one wrong comment remaining I think. Something like

Quoted 16 lines

hw/virtio/virtio-balloon.c static void virtio_balloon_free_page_stop(VirtIOBalloon *s) · line 558

Quoted 12 lines

hw/virtio/virtio-balloon.c +2 -2

index a1d6fb52c8..1b2127c04c 100644
@@ -554,8 +554,8 @@ static void virtio_balloon_free_page_stop(VirtIOBalloon *s)
          */
         qemu_mutex_lock(&s->free_page_lock);
         /*
-         * The guest hasn't done the reporting, so host sends a notification
-         * to the guest to actively stop the reporting.
+         * The guest isn't done with hinting, so the host sends a notification
+         * to the guest to actively stop the hinting.

I'll probably tweak it slightly and drop the "with". So the comment will read:
/*
* The guest isn't done hinting, so host sends a notification

Quoted 2 lines

I always feel like "so host sends" sounds wrong ("the host"). But I am not a native speaker.

Actually it might read better to get rid of "the host" entirely to make it more of an imperative statement rather than a declarative one. Maybe something more like:
/*
* The guest isn't done hinting, so send a notification
* to the guest to actively stop the hinting.
*/

From: Alexander Duyck <[email protected]>

We need to make certain to advertise support for page poison reporting if we want to actually get data on if the guest will be poisoning pages.

Add a value for reporting the poison value being used if page poisoning is enabled in the guest. With this we can determine if we will need to skip free page reporting when it is enabled in the future.

The value currently has no impact on existing balloon interfaces. In the case of existing balloon interfaces the onus is on the guest driver to reapply whatever poison is in place.

When we add free page reporting the poison value is used to determine if we can perform in-place page reporting. The expectation is that a reported page will already contain the value specified by the poison, and the reporting of the page should not change that value.

Signed-off-by Alexander Duyck <[email protected]>

---
 hw/virtio/virtio-balloon.c         |   29 +++++++++++++++++++++++++++++
 include/hw/virtio/virtio-balloon.h |    1 +
 2 files changed, 30 insertions(+)

hw/virtio/virtio-balloon.c +29 -0

index a1d6fb52c876..c1c76ec09c95 100644
@@ -634,6 +634,7 @@ 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);
+    config.poison_val = cpu_to_le32(dev->poison_val);
 
     if (dev->free_page_hint_status == FREE_PAGE_HINT_S_REQUESTED) {
         config.free_page_hint_cmd_id =

@@ -683,6 +684,14 @@ static ram_addr_t get_current_ram_size(void)
     return size;
 }
 
+static bool virtio_balloon_page_poison_support(void *opaque)
+{
+    VirtIOBalloon *s = opaque;
+    VirtIODevice *vdev = VIRTIO_DEVICE(s);
+
+    return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
+}
+
 static void virtio_balloon_set_config(VirtIODevice *vdev,
                                       const uint8_t *config_data)
 {

@@ -697,6 +706,10 @@ static void virtio_balloon_set_config(VirtIODevice *vdev,
         qapi_event_send_balloon_change(vm_ram_size -
                         ((ram_addr_t) dev->actual << VIRTIO_BALLOON_PFN_SHIFT));
     }
+    dev->poison_val = 0;
+    if (virtio_balloon_page_poison_support(dev)) {
+        dev->poison_val = le32_to_cpu(config.poison_val);
+    }
     trace_virtio_balloon_set_config(dev->actual, oldactual);
 }
 

@@ -755,6 +768,17 @@ static const VMStateDescription vmstate_virtio_balloon_free_page_hint = {
     }
 };
 
+static const VMStateDescription vmstate_virtio_balloon_page_poison = {
+    .name = "vitio-balloon-device/page-poison",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = virtio_balloon_page_poison_support,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(poison_val, VirtIOBalloon),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static const VMStateDescription vmstate_virtio_balloon_device = {
     .name = "virtio-balloon-device",
     .version_id = 1,

@@ -767,6 +791,7 @@ static const VMStateDescription vmstate_virtio_balloon_device = {
     },
     .subsections = (const VMStateDescription * []) {
         &vmstate_virtio_balloon_free_page_hint,
+        &vmstate_virtio_balloon_page_poison,
         NULL
     }
 };

@@ -854,6 +879,8 @@ static void virtio_balloon_device_reset(VirtIODevice *vdev)
         g_free(s->stats_vq_elem);
         s->stats_vq_elem = NULL;
     }
+
+    s->poison_val = 0;
 }
 
 static void virtio_balloon_set_status(VirtIODevice *vdev, uint8_t status)

@@ -916,6 +943,8 @@ static Property virtio_balloon_properties[] = {
                     VIRTIO_BALLOON_F_DEFLATE_ON_OOM, false),
     DEFINE_PROP_BIT("free-page-hint", VirtIOBalloon, host_features,
                     VIRTIO_BALLOON_F_FREE_PAGE_HINT, false),
+    DEFINE_PROP_BIT("page-poison", VirtIOBalloon, host_features,
+                    VIRTIO_BALLOON_F_PAGE_POISON, true),
     /* QEMU 4.0 accidentally changed the config size even when free-page-hint
      * is disabled, resulting in QEMU 3.1 migration incompatibility.  This
      * property retains this quirk for QEMU 4.1 machine types.

include/hw/virtio/virtio-balloon.h +0 -0

index 108cff97e71a..3ca2a78e1aca 100644

From: Alexander Duyck <[email protected]>

Add support for free page reporting. The idea is to function very similar to how the balloon works in that we basically end up madvising the page as not being used. However we don't really need to bother with any deflate type logic since the page will be faulted back into the guest when it is read or written to.

This provides a new way of letting the guest proactively report free pages to the hypervisor, so the hypervisor can reuse them. In contrast to inflate/deflate that is triggered via the hypervisor explicitly.

Signed-off-by Alexander Duyck <[email protected]>

---
 hw/virtio/virtio-balloon.c         |   67 ++++++++++++++++++++++++++++++++++++
 include/hw/virtio/virtio-balloon.h |    2 +
 2 files changed, 68 insertions(+), 1 deletion(-)

hw/virtio/virtio-balloon.c +67 -0

index c1c76ec09c95..2ce56c6c0794 100644
@@ -321,6 +321,67 @@ static void balloon_stats_set_poll_interval(Object *obj, Visitor *v,
     balloon_stats_change_timer(s, 0);
 }
 
+static void virtio_balloon_handle_report(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
+    VirtQueueElement *elem;
+
+    while ((elem = virtqueue_pop(vq, sizeof(VirtQueueElement)))) {
+        unsigned int i;
+
+        /*
+         * When we discard the page it has the effect of removing the page
+         * from the hypervisor itself and causing it to be zeroed when it
+         * is returned to us. So we must not discard the page if it is
+         * accessible by another device or process, or if the guest is
+         * expecting it to retain a non-zero value.
+         */
+        if (qemu_balloon_is_inhibited() || dev->poison_val) {
+            goto skip_element;
+        }
+
+        for (i = 0; i < elem->in_num; i++) {
+            void *addr = elem->in_sg[i].iov_base;
+            size_t size = elem->in_sg[i].iov_len;
+            ram_addr_t ram_offset;
+            RAMBlock *rb;
+
+            /*
+             * There is no need to check the memory section to see if
+             * it is ram/readonly/romd like there is for handle_output
+             * below. If the region is not meant to be written to then
+             * address_space_map will have allocated a bounce buffer
+             * and it will be freed in address_space_unmap and trigger
+             * and unassigned_mem_write before failing to copy over the
+             * buffer. If more than one bad descriptor is provided it
+             * will return NULL after the first bounce buffer and fail
+             * to map any resources.
+             */
+            rb = qemu_ram_block_from_host(addr, false, &ram_offset);
+            if (!rb) {
+                trace_virtio_balloon_bad_addr(elem->in_addr[i]);
+                continue;
+            }
+
+            /*
+             * For now we will simply ignore unaligned memory regions, or
+             * regions that overrun the end of the RAMBlock.
+             */
+            if (!QEMU_IS_ALIGNED(ram_offset | size, qemu_ram_pagesize(rb)) ||
+                (ram_offset + size) > qemu_ram_get_used_length(rb)) {
+                continue;
+            }
+
+            ram_block_discard_range(rb, ram_offset, size);
+        }
+
+skip_element:
+        virtqueue_push(vq, elem, 0);
+        virtio_notify(vdev, vq);
+        g_free(elem);
+    }
+}
+
 static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
 {
     VirtIOBalloon *s = VIRTIO_BALLOON(vdev);

@@ -818,6 +879,10 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
     s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
     s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats);
 
+    if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_REPORTING)) {
+        s->rvq = virtio_add_queue(vdev, 32, virtio_balloon_handle_report);
+    }
+
     if (virtio_has_feature(s->host_features,
                            VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
         s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE,

@@ -945,6 +1010,8 @@ static Property virtio_balloon_properties[] = {
                     VIRTIO_BALLOON_F_FREE_PAGE_HINT, false),
     DEFINE_PROP_BIT("page-poison", VirtIOBalloon, host_features,
                     VIRTIO_BALLOON_F_PAGE_POISON, true),
+    DEFINE_PROP_BIT("free-page-reporting", VirtIOBalloon, host_features,
+                    VIRTIO_BALLOON_F_REPORTING, false),
     /* QEMU 4.0 accidentally changed the config size even when free-page-hint
      * is disabled, resulting in QEMU 3.1 migration incompatibility.  This
      * property retains this quirk for QEMU 4.1 machine types.

include/hw/virtio/virtio-balloon.h +0 -0

index 3ca2a78e1aca..ac4013d51010 100644

This series provides an asynchronous means of reporting free guest pages to QEMU through virtio-balloon so that the memory associated with those pages can be discarded and reused by other processes and/or guests on the host. Using this it is possible to avoid unnecessary I/O to disk and greatly improve performance in the case of memory overcommit on the host.

As a part of enabling this feature it was necessary to implement the page poison reporting feature which had been added to the kernel, but was not available in QEMU. This patch set adds it as a new device property "page-poison" which is enabled by default, and adds support for migrating the reported value.

I originally submitted this patch series back on February 11th 2020[1], but at that time I was focused primarily on the kernel portion of this patch set. However as of April 7th those patches are now included in Linus's kernel tree[2] and so I am submitting the QEMU pieces for inclusion.

[1]: https://lore.kernel.org/lkml/[email protected]/
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b0c504f154718904ae49349147e3b7e6ae91ffdc

Changes from v17:
Fixed typo in patch 1 title
Addressed white-space issues reported via checkpatch Added braces {} for two if statements to match expected coding style

Changes from v18:
Updated patches 2 and 3 based on input from dhildenb
Added comment to patch 2 describing what keeps us from reporting a bad page Added patch to address issue with ROM devices being directly writable

Changes from v19:
Added std-headers change to match changes pushed for linux kernel headers Added patch to remove "report" from page hinting code paths Updated comment to better explain why we disable hints w/ page poisoning Removed code that was modifying config size for poison vs hinting Dropped x-page-poison property
Added code to bounds check the reported region vs the RAM block Dropped patch for ROM devices as that was already pulled in by Paolo

Changes from v20:
Rearranged patches to push Linux header sync patches to front Removed association between free page hinting and VIRTIO_BALLOON_F_PAGE_POISON Added code to enable VIRTIO_BALLOON_F_PAGE_POISON if page reporting is enabled Fixed possible resource leak if poison or qemu_balloon_is_inhibited return true

Changes from v21:
Added ack for patch 3
Rewrote patch description for page poison reporting feature Made page-poison independent property and set to enabled by default Added logic to migrate poison_val
Added several comments in code to better explain features Switched free-page-reporting property to disabled by default

Except one minor nit, looks good to me. We'll have to take care of compat handling regarding patch #4 as soon as we have 5.0 compat machines in place.