[RFC QEMU PATCH] QEMU: Provide a interface for hinting based off of the balloon infrastructure

[Alexander Duyck]

From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>

So this is meant to be a simplification of the existing balloon interface
to use for providing hints to what memory needs to be freed. I am assuming
this is safe to do as the deflate logic does not actually appear to do very
much other than tracking what subpages have been released and which ones
haven't.

I suspect this is still a bit crude and will need some more work.
Suggestions welcome.

Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
---
 hw/virtio/trace-events                          |    1 
 hw/virtio/virtio-balloon.c                      |   85 +++++++++++++++++++++++
 include/hw/virtio/virtio-balloon.h              |    2 -
 include/standard-headers/linux/virtio_balloon.h |    1 
 4 files changed, 88 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/trace-events b/hw/virtio/trace-events
index e28ba48da621..b56daf460769 100644
--- a/hw/virtio/trace-events
+++ b/hw/virtio/trace-events
@@ -46,6 +46,7 @@ virtio_balloon_handle_output(const char *name, uint64_t gpa) "section name: %s g
 virtio_balloon_get_config(uint32_t num_pages, uint32_t actual) "num_pages: %d actual: %d"
 virtio_balloon_set_config(uint32_t actual, uint32_t oldactual) "actual: %d oldactual: %d"
 virtio_balloon_to_target(uint64_t target, uint32_t num_pages) "balloon target: 0x%"PRIx64" num_pages: %d"
+virtio_bubble_handle_output(const char *name, uint64_t gpa, uint64_t size) "section name: %s gpa: 0x%" PRIx64 " size: %" PRIx64
 
 # virtio-mmio.c
 virtio_mmio_read(uint64_t offset) "virtio_mmio_read offset 0x%" PRIx64
diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 2112874055fb..eb819ec8f436 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -34,6 +34,13 @@
 
 #define BALLOON_PAGE_SIZE  (1 << VIRTIO_BALLOON_PFN_SHIFT)
 
+struct guest_pages {
+	unsigned long pfn;
+	unsigned int order;
+};
+
+void page_hinting_request(uint64_t addr, uint32_t len);
+
 struct PartiallyBalloonedPage {
     RAMBlock *rb;
     ram_addr_t base;
@@ -328,6 +335,80 @@ static void balloon_stats_set_poll_interval(Object *obj, Visitor *v,
     balloon_stats_change_timer(s, 0);
 }
 
+static void bubble_inflate_page(VirtIOBalloon *balloon,
+                                MemoryRegion *mr, hwaddr offset, size_t size)
+{
+    void *addr = memory_region_get_ram_ptr(mr) + offset;
+    ram_addr_t ram_offset;
+    size_t rb_page_size;
+    RAMBlock *rb;
+
+    rb = qemu_ram_block_from_host(addr, false, &ram_offset);
+    rb_page_size = qemu_ram_pagesize(rb);
+
+    /* For now we will simply ignore unaligned memory regions */
+    if ((ram_offset | size) & (rb_page_size - 1))
+        return;
+
+    ram_block_discard_range(rb, ram_offset, size);
+}
+
+static void virtio_bubble_handle_output(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
+    VirtQueueElement *elem;
+    MemoryRegionSection section;
+
+    for (;;) {
+        size_t offset = 0;
+	struct {
+            uint32_t pfn;
+            uint32_t size;
+	} hint;
+
+        elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+        if (!elem) {
+            return;
+        }
+
+        while (iov_to_buf(elem->out_sg, elem->out_num, offset, &hint, 8) == 8) {
+            size_t size = virtio_ldl_p(vdev, &hint.size);
+            hwaddr pa = virtio_ldl_p(vdev, &hint.pfn);
+
+            offset += 8;
+
+            if (qemu_balloon_is_inhibited())
+                continue;
+
+            pa <<= VIRTIO_BALLOON_PFN_SHIFT;
+            size <<= VIRTIO_BALLOON_PFN_SHIFT;
+
+            section = memory_region_find(get_system_memory(), pa, size);
+            if (!section.mr) {
+                trace_virtio_balloon_bad_addr(pa);
+                continue;
+            }
+
+            if (!memory_region_is_ram(section.mr) ||
+                memory_region_is_rom(section.mr) ||
+                memory_region_is_romd(section.mr)) {
+                trace_virtio_balloon_bad_addr(pa);
+            } else {
+                trace_virtio_bubble_handle_output(memory_region_name(section.mr),
+                                                  pa, size);
+                bubble_inflate_page(s, section.mr,
+                                    section.offset_within_region, size);
+            }
+
+            memory_region_unref(section.mr);
+        }
+
+        virtqueue_push(vq, elem, offset);
+        virtio_notify(vdev, vq);
+        g_free(elem);
+    }
+}
+
 static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
 {
     VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
@@ -694,6 +775,7 @@ static uint64_t virtio_balloon_get_features(VirtIODevice *vdev, uint64_t f,
     VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
     f |= dev->host_features;
     virtio_add_feature(&f, VIRTIO_BALLOON_F_STATS_VQ);
+    virtio_add_feature(&f, VIRTIO_BALLOON_F_HINTING);
 
     return f;
 }
@@ -780,6 +862,7 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
     s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
     s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
     s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats);
+    s->hvq = virtio_add_queue(vdev, 128, virtio_bubble_handle_output);
 
     if (virtio_has_feature(s->host_features,
                            VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
@@ -875,6 +958,8 @@ static void virtio_balloon_instance_init(Object *obj)
 
     object_property_add(obj, "guest-stats", "guest statistics",
                         balloon_stats_get_all, NULL, NULL, s, NULL);
+    object_property_add(obj, "guest-page-hinting", "guest page hinting",
+                        NULL, NULL, NULL, s, NULL);
 
     object_property_add(obj, "guest-stats-polling-interval", "int",
                         balloon_stats_get_poll_interval,
diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
index 1afafb12f6bc..dd6d4d0e45fd 100644
--- a/include/hw/virtio/virtio-balloon.h
+++ b/include/hw/virtio/virtio-balloon.h
@@ -44,7 +44,7 @@ enum virtio_balloon_free_page_report_status {
 
 typedef struct VirtIOBalloon {
     VirtIODevice parent_obj;
-    VirtQueue *ivq, *dvq, *svq, *free_page_vq;
+    VirtQueue *ivq, *dvq, *svq, *hvq, *free_page_vq;
     uint32_t free_page_report_status;
     uint32_t num_pages;
     uint32_t actual;
diff --git a/include/standard-headers/linux/virtio_balloon.h b/include/standard-headers/linux/virtio_balloon.h
index 9375ca2a70de..f9e3e8256261 100644
--- a/include/standard-headers/linux/virtio_balloon.h
+++ b/include/standard-headers/linux/virtio_balloon.h
@@ -36,6 +36,7 @@
 #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM	2 /* Deflate balloon on OOM */
 #define VIRTIO_BALLOON_F_FREE_PAGE_HINT	3 /* VQ to report free pages */
 #define VIRTIO_BALLOON_F_PAGE_POISON	4 /* Guest is using page poisoning */
+#define VIRTIO_BALLOON_F_HINTING	5 /* Page hinting virtqueue */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12