[PATCH] kvm: Support for guest page hinting

[nilal@redhat.com]

From: Nitesh Narayan Lal <nilal@redhat.com>

This patch enables QEMU to handle page hinting requests
from the guest. Once the guest kicks QEMU to free a page,
QEMU retrives the guest physical address and converts it to
host virtual address and then MADVISE that memory.

Signed-off-by: Nitesh Narayan Lal <nilal@redhat.com>
---
 hw/virtio/virtio-balloon.c         | 54 ++++++++++++++++++++++++++++++++++++++
 hw/virtio/virtio.c                 | 24 +++++++++++++++++
 include/hw/virtio/virtio-access.h  |  1 +
 include/hw/virtio/virtio-balloon.h |  2 +-
 include/qemu/osdep.h               |  7 +++++
 5 files changed, 87 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 37cde38..a0e3c41 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -33,6 +33,8 @@
 
 #define BALLOON_PAGE_SIZE  (1 << VIRTIO_BALLOON_PFN_SHIFT)
 
+void page_hinting_request(uint64_t addr, uint32_t len);
+
 static void balloon_page(void *addr, int deflate)
 {
     if (!qemu_balloon_is_inhibited() && (!kvm_enabled() ||
@@ -205,6 +207,57 @@ 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;
+    void *ptr;
+    int ret = 0;
+
+    /*ptr is the host physical address*/
+    ptr = gpa2hva(&mr, addr, &local_err);
+    if (local_err) {
+        error_report_err(local_err);
+        return;
+    }
+    ret = qemu_madvise((void *)ptr, len, QEMU_MADV_FREE);
+    if (ret == -1)
+	    printf("\n%d:%s Error: Madvise failed with error:%d\n", __LINE__, __func__, ret);
+}
+
+
+static void virtio_balloon_page_hinting(VirtIODevice *vdev, VirtQueue *vq)
+{
+    uint64_t addr;
+    uint32_t len;
+    VirtQueueElement elem = {};
+
+    pop_hinting_addr(vq, &addr, &len);
+    page_hinting_request(addr, len);
+    virtqueue_push(vq, &elem, 0);
+    virtio_notify(vdev, vq);
+}
+
 static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
 {
     VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
@@ -443,6 +496,7 @@ 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);
 }
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 311929e..24e26ec 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -825,6 +825,30 @@ static void *virtqueue_alloc_element(size_t sz, unsigned out_num, unsigned in_nu
     return elem;
 }
 
+void pop_hinting_addr(VirtQueue *vq, uint64_t *addr, uint32_t *len)
+{
+   VRingMemoryRegionCaches *caches;
+   VRingDesc desc;
+   MemoryRegionCache *desc_cache;
+   VirtIODevice *vdev = vq->vdev;
+   unsigned int head, i, max;
+
+   max = vq->vring.num;
+   if (!virtqueue_get_head(vq, vq->last_avail_idx++, &head)) {
+	printf("\n%d:%sError: Unable to read head\n", __LINE__, __func__);
+   }
+   i = head;
+
+   caches = vring_get_region_caches(vq);
+   if (caches->desc.len < max * sizeof(VRingDesc)) {
+       virtio_error(vdev, "Cannot map descriptor ring");
+   }
+   desc_cache = &caches->desc;
+   vring_desc_read(vdev, &desc, desc_cache, i);
+   *addr = desc.addr;
+   *len = desc.len;
+}
+
 void *virtqueue_pop(VirtQueue *vq, size_t sz)
 {
     unsigned int i, head, max;
diff --git a/include/hw/virtio/virtio-access.h b/include/hw/virtio/virtio-access.h
index 2e92074..568d71f 100644
--- a/include/hw/virtio/virtio-access.h
+++ b/include/hw/virtio/virtio-access.h
@@ -24,6 +24,7 @@
 #define LEGACY_VIRTIO_IS_BIENDIAN 1
 #endif
 
+void pop_hinting_addr(VirtQueue *vq, uint64_t *addr, uint32_t *len);
 static inline bool virtio_access_is_big_endian(VirtIODevice *vdev)
 {
 #if defined(LEGACY_VIRTIO_IS_BIENDIAN)
diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
index 1ea13bd..dfb5782 100644
--- a/include/hw/virtio/virtio-balloon.h
+++ b/include/hw/virtio/virtio-balloon.h
@@ -33,7 +33,7 @@ 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/qemu/osdep.h b/include/qemu/osdep.h
index 9dd318a..033d64c 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -278,6 +278,11 @@ void qemu_anon_ram_free(void *ptr, size_t size);
 #else
 #define QEMU_MADV_REMOVE QEMU_MADV_INVALID
 #endif
+#ifdef MADV_FREE
+#define QEMU_MADV_FREE MADV_FREE
+#else
+#define QEMU_MADV_FREE QEMU_MAD_INVALID
+#endif
 
 #elif defined(CONFIG_POSIX_MADVISE)
 
@@ -291,6 +296,7 @@ void qemu_anon_ram_free(void *ptr, size_t size);
 #define QEMU_MADV_HUGEPAGE  QEMU_MADV_INVALID
 #define QEMU_MADV_NOHUGEPAGE  QEMU_MADV_INVALID
 #define QEMU_MADV_REMOVE QEMU_MADV_INVALID
+#define QEMU_MADV_FREE QEMU_MAD_INVALID
 
 #else /* no-op */
 
@@ -304,6 +310,7 @@ void qemu_anon_ram_free(void *ptr, size_t size);
 #define QEMU_MADV_HUGEPAGE  QEMU_MADV_INVALID
 #define QEMU_MADV_NOHUGEPAGE  QEMU_MADV_INVALID
 #define QEMU_MADV_REMOVE QEMU_MADV_INVALID
+#define QEMU_MADV_FREE QEMU_MAD_INVALID
 
 #endif
 
-- 
2.9.4