Linux Virtualization - Feb 2010 - [PATCH 0/3] vhost: logging fixes

The following patches on top of net-next fix issues related to write
logging in vhost. This fixes all known to me logging issues, migration
now works for me while under stress in both TX and RX directions.
Rusty's going on vacation, I am guessing he won't have time to review
this: Gleb, Juan, Herbert, could one of you review this patchset please?

There's also the send queue full issue reported by
Sridhar Samudrala which I'm testing various fixes for,
that patch is contained to vhost/net though,
so there's no conflict, patch will be posted separately.


Michael S. Tsirkin (3):
  vhost: logging thinko fix
  vhost: initialize log eventfd context pointer
  vhost: fix get_user_pages_fast error handling

 drivers/vhost/vhost.c |   14 +++++++++-----
 1 files changed, 9 insertions(+), 5 deletions(-)

vhost was dong some complex math to get
offset to log at, and got it wrong by a couple of bytes,
while in fact it's simple: get address where we write,
subtract start of buffer, add log base.

Do it this way.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 drivers/vhost/vhost.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 6eb1525..c767279 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1004,10 +1004,12 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned
int head, int len)
 	if (unlikely(vq->log_used)) {
 		/* Make sure data is seen before log. */
 		smp_wmb();
-		log_write(vq->log_base, vq->log_addr + sizeof *vq->used->ring *
-			  (vq->last_used_idx % vq->num),
-			  sizeof *vq->used->ring);
-		log_write(vq->log_base, vq->log_addr, sizeof *vq->used->ring);
+		log_write(vq->log_base,
+			  vq->log_addr + ((void *)used - (void *)vq->used),
+			  sizeof *used);
+		log_write(vq->log_base,
+			  vq->log_addr + offsetof(struct vring_used, idx),
+			  sizeof vq->used->idx);
 		if (vq->log_ctx)
 			eventfd_signal(vq->log_ctx, 1);
 	}
-- 
1.7.0.18.g0d53a5

vq log eventfd context pointer needs to be initialized, otherwise
operation may fail or oops if log is enabled but log eventfd not set by
userspace.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 drivers/vhost/vhost.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c767279..d4f8fdf 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -121,6 +121,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 	vq->kick = NULL;
 	vq->call_ctx = NULL;
 	vq->call = NULL;
+	vq->log_ctx = NULL;
 }
 
 long vhost_dev_init(struct vhost_dev *dev,
-- 
1.7.0.18.g0d53a5

get_user_pages_fast returns number of pages on success, negative value
on failure, but never 0. Fix vhost code to match this logic.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 drivers/vhost/vhost.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index d4f8fdf..d003504 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -646,8 +646,9 @@ static int set_bit_to_user(int nr, void __user *addr)
 	int bit = nr + (log % PAGE_SIZE) * 8;
 	int r;
 	r = get_user_pages_fast(log, 1, 1, &page);
-	if (r)
+	if (r < 0)
 		return r;
+	BUG_ON(r != 1);
 	base = kmap_atomic(page, KM_USER0);
 	set_bit(bit, base);
 	kunmap_atomic(base, KM_USER0);
-- 
1.7.0.18.g0d53a5