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Re: [Qemu-devel] [PATCH v2 for-2.3] virtio-blk: correctly dirty guest me


From: Li Zhijian
Subject: Re: [Qemu-devel] [PATCH v2 for-2.3] virtio-blk: correctly dirty guest memory
Date: Fri, 3 Apr 2015 12:13:29 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

On 04/03/2015 01:50 AM, Paolo Bonzini wrote:
After qemu_iovec_destroy, the QEMUIOVector's size is zeroed and
the zero size ultimately is used to compute virtqueue_push's len
argument.  Therefore, reads from virtio-blk devices did not
migrate their results correctly.  (Writes were okay).

Save the size in virtio_blk_handle_request, and use it when the request
is completed.

Based on a patch by Wen Congyang.

Signed-off-by: Wen Congyang <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
Tested-by: Li Zhijian <address@hidden>

Thanks
Li Zhijian


---
  hw/block/dataplane/virtio-blk.c |  3 +--
  hw/block/virtio-blk.c           | 13 ++++++++++++-
  include/hw/virtio/virtio-blk.h  |  1 +
  3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index cd41478..3db139b 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -77,8 +77,7 @@ static void complete_request_vring(VirtIOBlockReq *req, 
unsigned char status)
      VirtIOBlockDataPlane *s = req->dev->dataplane;
      stb_p(&req->in->status, status);
- vring_push(s->vdev, &req->dev->dataplane->vring, &req->elem,
-               req->qiov.size + sizeof(*req->in));
+    vring_push(s->vdev, &req->dev->dataplane->vring, &req->elem, req->in_len);
/* Suppress notification to guest by BH and its scheduled
       * flag because requests are completed as a batch after io
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 000c38d..9546fd2 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -33,6 +33,7 @@ VirtIOBlockReq *virtio_blk_alloc_request(VirtIOBlock *s)
      VirtIOBlockReq *req = g_slice_new(VirtIOBlockReq);
      req->dev = s;
      req->qiov.size = 0;
+    req->in_len = 0;
      req->next = NULL;
      req->mr_next = NULL;
      return req;
@@ -54,7 +55,7 @@ static void virtio_blk_complete_request(VirtIOBlockReq *req,
      trace_virtio_blk_req_complete(req, status);
stb_p(&req->in->status, status);
-    virtqueue_push(s->vq, &req->elem, req->qiov.size + sizeof(*req->in));
+    virtqueue_push(s->vq, &req->elem, req->in_len);
      virtio_notify(vdev, s->vq);
  }
@@ -102,6 +103,14 @@ static void virtio_blk_rw_complete(void *opaque, int ret)
          if (ret) {
              int p = virtio_ldl_p(VIRTIO_DEVICE(req->dev), &req->out.type);
              bool is_read = !(p & VIRTIO_BLK_T_OUT);
+            /* Note that memory may be dirtied on read failure.  If the
+             * virtio request is not completed here, as is the case for
+             * BLOCK_ERROR_ACTION_STOP, the memory may not be copied
+             * correctly during live migration.  While this is ugly,
+             * it is acceptable because the device is free to write to
+             * the memory until the request is completed (which will
+             * happen on the other side of the migration).
+             */
              if (virtio_blk_handle_rw_error(req, -ret, is_read)) {
                  continue;
              }
@@ -496,6 +505,8 @@ void virtio_blk_handle_request(VirtIOBlockReq *req, 
MultiReqBuffer *mrb)
          exit(1);
      }
+ /* We always touch the last byte, so just see how big in_iov is. */
+    req->in_len = iov_size(in_iov, in_num);
      req->in = (void *)in_iov[in_num - 1].iov_base
                + in_iov[in_num - 1].iov_len
                - sizeof(struct virtio_blk_inhdr);
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index b3ffcd9..6bf5905 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -67,6 +67,7 @@ typedef struct VirtIOBlockReq {
      struct virtio_blk_inhdr *in;
      struct virtio_blk_outhdr out;
      QEMUIOVector qiov;
+    size_t in_len;
      struct VirtIOBlockReq *next;
      struct VirtIOBlockReq *mr_next;
      BlockAcctCookie acct;


--
Best regards.
Li Zhijian (8555)




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