[PATCH] vhost: set dirty log when updating flags of used ring

[Jason Wang]

We need to set log when updating flags of used ring, otherwise they may
be missed after migration. A helper was introduced to write used_flags
back to guest memory and update the log if necessary.

Signed-off-by: Jason Wang <jasow...@redhat.com>
---
 drivers/vhost/vhost.c |   26 ++++++++++++++++++++++----
 drivers/vhost/vhost.h |    2 ++
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 2ab2912..7c46aed 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -573,8 +573,10 @@ static long vhost_set_memory(struct vhost_dev *d, struct 
vhost_memory __user *m)
 static int init_used(struct vhost_virtqueue *vq,
                     struct vring_used __user *used)
 {
-       int r = put_user(vq->used_flags, &used->flags);
+       int r;
 
+       vq->used = used;
+       r = vhost_update_used_flags(vq);
        if (r)
                return r;
        return get_user(vq->last_used_idx, &used->idx);
@@ -700,7 +702,6 @@ static long vhost_set_vring(struct vhost_dev *d, int ioctl, 
void __user *argp)
                vq->desc = (void __user *)(unsigned long)a.desc_user_addr;
                vq->avail = (void __user *)(unsigned long)a.avail_user_addr;
                vq->log_addr = a.log_guest_addr;
-               vq->used = (void __user *)(unsigned long)a.used_user_addr;
                break;
        case VHOST_SET_VRING_KICK:
                if (copy_from_user(&f, argp, sizeof f)) {
@@ -1375,6 +1376,23 @@ void vhost_add_used_and_signal_n(struct vhost_dev *dev,
        vhost_signal(dev, vq);
 }
 
+int vhost_update_used_flags(struct vhost_virtqueue *vq)
+{
+       if (put_user(vq->used_flags, &vq->used->flags) < 0)
+               return -EFAULT;
+       if (unlikely(vq->log_used)) {
+               /* Make sure the flag is seen before log. */
+               smp_wmb();
+               /* Log used flag write. */
+               log_write(vq->log_base,
+                         vq->log_addr + offsetof(struct vring_used, flags),
+                         sizeof vq->used->flags);
+               if (vq->log_ctx)
+                       eventfd_signal(vq->log_ctx, 1);
+       }
+       return 0;
+}
+
 /* OK, now we need to know about added descriptors. */
 bool vhost_enable_notify(struct vhost_virtqueue *vq)
 {
@@ -1384,7 +1402,7 @@ bool vhost_enable_notify(struct vhost_virtqueue *vq)
        if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
                return false;
        vq->used_flags &= ~VRING_USED_F_NO_NOTIFY;
-       r = put_user(vq->used_flags, &vq->used->flags);
+       r = vhost_update_used_flags(vq);
        if (r) {
                vq_err(vq, "Failed to enable notification at %p: %d\n",
                       &vq->used->flags, r);
@@ -1411,7 +1429,7 @@ void vhost_disable_notify(struct vhost_virtqueue *vq)
        if (vq->used_flags & VRING_USED_F_NO_NOTIFY)
                return;
        vq->used_flags |= VRING_USED_F_NO_NOTIFY;
-       r = put_user(vq->used_flags, &vq->used->flags);
+       r = vhost_update_used_flags(vq);
        if (r)
                vq_err(vq, "Failed to enable notification at %p: %d\n",
                       &vq->used->flags, r);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index b3363ae..76f4c61 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -155,6 +155,8 @@ bool vhost_enable_notify(struct vhost_virtqueue *);
 int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
                    unsigned int log_num, u64 len);
 
+int vhost_update_used_flags(struct vhost_virtqueue *vq);
+
 #define vq_err(vq, fmt, ...) do {                                  \
                pr_debug(pr_fmt(fmt), ##__VA_ARGS__);       \
                if ((vq)->error_ctx)                               \

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linux-foundation.org/mailman/listinfo/virtualization