[RFC][QEMU Patch] KVM: Enable QEMU to free the pages hinted by the guest

[Nitesh Narayan Lal <nitesh@redhat.com>]

This patch enables QEMU to perform MADVISE_DONTNEED on the pages
reported by the guest.

Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
---
 hw/virtio/trace-events                        |  1 +
 hw/virtio/virtio-balloon.c                    | 90 +++++++++++++++++++
 include/hw/virtio/virtio-balloon.h            |  2 +-
 .../standard-headers/linux/virtio_balloon.h   |  1 +
 4 files changed, 93 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/trace-events b/hw/virtio/trace-events
index 07bcbe9e85..e3ab66f126 100644
--- a/hw/virtio/trace-events
+++ b/hw/virtio/trace-events
@@ -46,3 +46,4 @@ 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_balloon_hinting_request(unsigned long pfn, unsigned int num_pages) "Guest page hinting request: %lu num_pages: %d"
diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index a12677d4d5..7ab1471017 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -33,6 +33,13 @@
 
 #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);
+
 static void balloon_page(void *addr, int deflate)
 {
     if (!qemu_balloon_is_inhibited()) {
@@ -207,6 +214,85 @@ static void balloon_stats_set_poll_interval(Object *obj, Visitor *v,
     balloon_stats_change_timer(s, 0);
 }
 
+static void *gpa2hva(MemoryRegion **p_mr, hwaddr addr, Error **errp)
+{
+    MemoryRegionSection mrs = memory_region_find(get_system_memory(),
+                                                 addr, 1);
+
+    if (!mrs.mr) {
+        error_setg(errp, "No memory is mapped at address 0x%" HWADDR_PRIx, addr);
+        return NULL;
+    }
+
+    if (!memory_region_is_ram(mrs.mr) && !memory_region_is_romd(mrs.mr)) {
+        error_setg(errp, "Memory at address 0x%" HWADDR_PRIx "is not RAM", addr);
+        memory_region_unref(mrs.mr);
+        return NULL;
+    }
+
+    *p_mr = mrs.mr;
+    return qemu_map_ram_ptr(mrs.mr->ram_block, mrs.offset_within_region);
+}
+
+void page_hinting_request(uint64_t addr, uint32_t len)
+{
+    Error *local_err = NULL;
+    MemoryRegion *mr = NULL;
+    int ret = 0;
+    struct guest_pages *guest_obj;
+    int i = 0;
+    void *hvaddr_to_free;
+    unsigned long pfn, pfn_end;
+    uint64_t gpaddr_to_free;
+    void * temp_addr = gpa2hva(&mr, addr, &local_err);
+
+    if (local_err) {
+        error_report_err(local_err);
+        return;
+    }
+    guest_obj = temp_addr;
+    while (i < len) {
+        pfn = guest_obj[i].pfn;
+	pfn_end = guest_obj[i].pfn + (1 << guest_obj[i].order) - 1;
+	trace_virtio_balloon_hinting_request(pfn,(1 << guest_obj[i].order));
+	while (pfn <= pfn_end) {
+	        gpaddr_to_free = pfn << VIRTIO_BALLOON_PFN_SHIFT;
+	        hvaddr_to_free = gpa2hva(&mr, gpaddr_to_free, &local_err);
+	        if (local_err) {
+			error_report_err(local_err);
+		        return;
+		}
+		ret = qemu_madvise((void *)hvaddr_to_free, 4096, QEMU_MADV_DONTNEED);
+		if (ret == -1)
+		    printf("\n%d:%s Error: Madvise failed with error:%d\n", __LINE__, __func__, ret);
+		pfn++;
+	}
+	i++;
+    }
+}
+
+static void virtio_balloon_page_hinting(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtQueueElement *elem = NULL;
+    uint64_t temp_addr;
+    uint32_t temp_len;
+    size_t size, t_size = 0;
+
+    elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+    if (!elem) {
+	printf("\npop error\n");
+	return;
+    }
+    size = iov_to_buf(elem->out_sg, elem->out_num, 0, &temp_addr, sizeof(temp_addr));
+    t_size += size;
+    size = iov_to_buf(elem->out_sg, elem->out_num, 8, &temp_len, sizeof(temp_len));
+    t_size += size;
+    page_hinting_request(temp_addr, temp_len);
+    virtqueue_push(vq, elem, t_size);
+    virtio_notify(vdev, vq);
+    g_free(elem);
+}
+
 static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
 {
     VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
@@ -376,6 +462,7 @@ 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;
 }
 
@@ -445,6 +532,7 @@ 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_balloon_page_hinting);
 
     reset_stats(s);
 }
@@ -488,6 +576,8 @@ 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 e0df3528c8..774498a6ca 100644
--- a/include/hw/virtio/virtio-balloon.h
+++ b/include/hw/virtio/virtio-balloon.h
@@ -32,7 +32,7 @@ typedef struct virtio_balloon_stat_modern {
 
 typedef struct VirtIOBalloon {
     VirtIODevice parent_obj;
-    VirtQueue *ivq, *dvq, *svq;
+    VirtQueue *ivq, *dvq, *svq, *hvq;
     uint32_t num_pages;
     uint32_t actual;
     uint64_t stats[VIRTIO_BALLOON_S_NR];
diff --git a/include/standard-headers/linux/virtio_balloon.h b/include/standard-headers/linux/virtio_balloon.h
index 4dbb7dc6c0..f50c0d95ea 100644
--- a/include/standard-headers/linux/virtio_balloon.h
+++ b/include/standard-headers/linux/virtio_balloon.h
@@ -34,6 +34,7 @@
 #define VIRTIO_BALLOON_F_MUST_TELL_HOST	0 /* Tell before reclaiming pages */
 #define VIRTIO_BALLOON_F_STATS_VQ	1 /* Memory Stats virtqueue */
 #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM	2 /* Deflate balloon on OOM */
+#define VIRTIO_BALLOON_F_HINTING	5 /* Page hinting virtqueue */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12
-- 
2.17.2