virtio-balloon: add support for providing free page reports to host

Add support for the page reporting feature provided by virtio-balloon.
Reporting differs from the regular balloon functionality in that is is
much less durable than a standard memory balloon.  Instead of creating a
list of pages that cannot be accessed the pages are only inaccessible
while they are being indicated to the virtio interface.  Once the
interface has acknowledged them they are placed back into their respective
free lists and are once again accessible by the guest system.

Unlike a standard balloon we don't inflate and deflate the pages.  Instead
we perform the reporting, and once the reporting is completed it is
assumed that the page has been dropped from the guest and will be faulted
back in the next time the page is accessed.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Nitesh Narayan Lal <nitesh@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pankaj Gupta <pagupta@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Wang <wei.w.wang@intel.com>
Cc: Yang Zhang <yang.zhang.wz@gmail.com>
Cc: wei qi <weiqi4@huawei.com>
Link: http://lkml.kernel.org/r/20200211224657.29318.68624.stgit@localhost.localdomain
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 078615cf2afcd5f818a5cd26af5137e38f8b6041..4b2dd8259ff515e5a4a6c3d5c59271a9f92062e0 100644 (file)
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -58,6 +58,7 @@ config VIRTIO_BALLOON
        tristate "Virtio balloon driver"
        depends on VIRTIO
        select MEMORY_BALLOON
+       select PAGE_REPORTING
        ---help---
         This driver supports increasing and decreasing the amount
         of memory within a KVM guest.

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index e41a62d84260894101e8b2b5fe0efdfa772b26e5..9e0177529bad34d81137558f64de217af999b715 100644 (file)
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -19,6 +19,7 @@
 #include <linux/mount.h>
 #include <linux/magic.h>
 #include <linux/pseudo_fs.h>
+#include <linux/page_reporting.h>
 
 /*
  * Balloon device works in 4K page units.  So each page is pointed to by
@@ -47,6 +48,7 @@ enum virtio_balloon_vq {
        VIRTIO_BALLOON_VQ_DEFLATE,
        VIRTIO_BALLOON_VQ_STATS,
        VIRTIO_BALLOON_VQ_FREE_PAGE,
+       VIRTIO_BALLOON_VQ_REPORTING,
        VIRTIO_BALLOON_VQ_MAX
 };
 
@@ -114,6 +116,10 @@ struct virtio_balloon {
 
        /* To register a shrinker to shrink memory upon memory pressure */
        struct shrinker shrinker;
+
+       /* Free page reporting device */
+       struct virtqueue *reporting_vq;
+       struct page_reporting_dev_info pr_dev_info;
 };
 
 static struct virtio_device_id id_table[] = {
@@ -153,6 +159,33 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
 
 }
 
+int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_info,
+                                  struct scatterlist *sg, unsigned int nents)
+{
+       struct virtio_balloon *vb =
+               container_of(pr_dev_info, struct virtio_balloon, pr_dev_info);
+       struct virtqueue *vq = vb->reporting_vq;
+       unsigned int unused, err;
+
+       /* We should always be able to add these buffers to an empty queue. */
+       err = virtqueue_add_inbuf(vq, sg, nents, vb, GFP_NOWAIT | __GFP_NOWARN);
+
+       /*
+        * In the extremely unlikely case that something has occurred and we
+        * are able to trigger an error we will simply display a warning
+        * and exit without actually processing the pages.
+        */
+       if (WARN_ON_ONCE(err))
+               return err;
+
+       virtqueue_kick(vq);
+
+       /* When host has read buffer, this completes via balloon_ack */
+       wait_event(vb->acked, virtqueue_get_buf(vq, &unused));
+
+       return 0;
+}
+
 static void set_page_pfns(struct virtio_balloon *vb,
                          __virtio32 pfns[], struct page *page)
 {
@@ -481,6 +514,7 @@ static int init_vqs(struct virtio_balloon *vb)
        names[VIRTIO_BALLOON_VQ_STATS] = NULL;
        callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
        names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
+       names[VIRTIO_BALLOON_VQ_REPORTING] = NULL;
 
        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
                names[VIRTIO_BALLOON_VQ_STATS] = "stats";
@@ -492,6 +526,11 @@ static int init_vqs(struct virtio_balloon *vb)
                callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
        }
 
+       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) {
+               names[VIRTIO_BALLOON_VQ_REPORTING] = "reporting_vq";
+               callbacks[VIRTIO_BALLOON_VQ_REPORTING] = balloon_ack;
+       }
+
        err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
                                         vqs, callbacks, names, NULL, NULL);
        if (err)
@@ -524,6 +563,9 @@ static int init_vqs(struct virtio_balloon *vb)
        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
                vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE];
 
+       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
+               vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING];
+
        return 0;
 }
 
@@ -953,12 +995,31 @@ static int virtballoon_probe(struct virtio_device *vdev)
                if (err)
                        goto out_del_balloon_wq;
        }
+
+       vb->pr_dev_info.report = virtballoon_free_page_report;
+       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) {
+               unsigned int capacity;
+
+               capacity = virtqueue_get_vring_size(vb->reporting_vq);
+               if (capacity < PAGE_REPORTING_CAPACITY) {
+                       err = -ENOSPC;
+                       goto out_unregister_shrinker;
+               }
+
+               err = page_reporting_register(&vb->pr_dev_info);
+               if (err)
+                       goto out_unregister_shrinker;
+       }
+
        virtio_device_ready(vdev);
 
        if (towards_target(vb))
                virtballoon_changed(vdev);
        return 0;
 
+out_unregister_shrinker:
+       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
+               virtio_balloon_unregister_shrinker(vb);
 out_del_balloon_wq:
        if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
                destroy_workqueue(vb->balloon_wq);
@@ -997,6 +1058,8 @@ static void virtballoon_remove(struct virtio_device *vdev)
 {
        struct virtio_balloon *vb = vdev->priv;
 
+       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
+               page_reporting_unregister(&vb->pr_dev_info);
        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
                virtio_balloon_unregister_shrinker(vb);
        spin_lock_irq(&vb->stop_update_lock);
@@ -1069,6 +1132,7 @@ static unsigned int features[] = {
        VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
        VIRTIO_BALLOON_F_FREE_PAGE_HINT,
        VIRTIO_BALLOON_F_PAGE_POISON,
+       VIRTIO_BALLOON_F_REPORTING,
 };
 
 static struct virtio_driver virtio_balloon_driver = {

diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
index a1966cd7b6774944a1d818bd823de0253c4a2908..19974392d3240fad6265dd7a7a6e045636268b17 100644 (file)
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/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_REPORTING     5 /* Page reporting virtqueue */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12