[PATCH v1 0/1] Memory hotplug fix

[PATCH v1 0/1] Memory hotplug fix

[Danylo Vodopianov]

Hi everyone.
We detected an issue with the memory hotplug feature and virtio devices while working with vitrio
in DPDK.In general, the issue is around the user request VHOST_USER_SET_MEM_TABLE and
locking queues for this request
(https://git.dpdk.org/dpdk-stable/tree/lib/vhost/vhost_user.c#n1512)
When the vhost_user receives the request VHOST_USER_SET_MEM_TABLE, it locks queues only
when the flag lock_all_qps is true(it is always true), AND the flag
VIRTIO_DEV_VDPA_CONFIGURED is not set.
https://git.dpdk.org/dpdk-stable/tree/lib/vhost/vhost_user.c#n3181
In the case of a memory hot plug, the flag VIRTIO_DEV_VDPA_CONFIGURED is always set,
and due to this, the queues are never locked while they are expected to be locked.
https://git.dpdk.org/dpdk-stable/tree/lib/vhost/vhost_user.c#n1512.
The quick solution is to add the check for request type and do lock queues always
if we have request VHOST_USER_SET_MEM_TABLE. Something like this, in general
https://git.dpdk.org/dpdk-stable/tree/lib/vhost/vhost_user.c#n3179

 if (!(dev->flags & VIRTIO_DEV_VDPA_CONFIGURED) ||
 request == VHOST_USER_SET_MEM_TABLE) {
 ...

Danylo Vodopianov (1):
  vhost: handle virtqueue locking for memory hotplug

 lib/vhost/vhost_user.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

-- 
2.43.5

[PATCH v1 1/1] vhost: handle virtqueue locking for memory hotplug

[Danylo Vodopianov]

For vDPA devices, virtqueues are not locked once the device has been
configured.
In the commit 5e8fcc60b59d
("vhost: enhance virtqueue access lock asserts"),
the asserts were enhanced to trigger rte_panic functionality, preventing
access to virtqueues without locking. However, this change introduced
an issue where the memory hotplug mechanism, added in the commit
127f9c6f7b78 ("vhost: handle memory hotplug with vDPA devices"),
no longer works. Since it expects for all queues are locked.

During the initialization of a vDPA device, the driver sets the
VIRTIO_DEV_VDPA_CONFIGURED flag, which prevents the
vhost_user_lock_all_queue_pairs function from locking the
virtqueues. This leads to the error: the VIRTIO_DEV_VDPA_CONFIGURED
flag allows the use of the hotplug mechanism, but it fails
because the virtqueues are not locked, while it expects to be locked
for VHOST_USER_SET_MEM_TABLE in the table VHOST_MESSAGE_HANDLERS.

This patch addresses the issue by enhancing the conditional statement
to include a new condition. Specifically, when the device receives the
VHOST_USER_SET_MEM_TABLE request, the virtqueues are locked to update
the basic configurations and hotplug the guest memory.

This fix does not impact access lock when vDPA driver is configured
for other unnecessary message handlers.

Manual memory configuring with "--socket-mem" option allows to avoid
hotplug mechanism using.

Signed-off-by: Danylo Vodopianov <dvo-plv@napatech.com>
---
 lib/vhost/vhost_user.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
index ec950acf97..16d03e1033 100644
--- a/lib/vhost/vhost_user.c
+++ b/lib/vhost/vhost_user.c
@@ -3178,7 +3178,13 @@ vhost_user_msg_handler(int vid, int fd)
 	 * would cause a dead lock.
 	 */
 	if (msg_handler != NULL && msg_handler->lock_all_qps) {
-		if (!(dev->flags & VIRTIO_DEV_VDPA_CONFIGURED)) {
+		/* Lock all queue pairs if the device is not configured for vDPA,
+		 * or if it is configured for vDPA but the request is VHOST_USER_SET_MEM_TABLE.
+		 * This ensures proper queue locking for memory table updates and guest
+		 * memory hotplug.
+		 */
+		if (!(dev->flags & VIRTIO_DEV_VDPA_CONFIGURED) ||
+			request == VHOST_USER_SET_MEM_TABLE) {
 			vhost_user_lock_all_queue_pairs(dev);
 			unlock_required = 1;
 		}
-- 
2.43.5

[PATCH v1 1/1] vhost: handle virtqueue locking for memory hotplug

[Danylo Vodopianov]

For vDPA devices, virtqueues are not locked once the device has been
configured.
In the commit 5e8fcc60b59d
("vhost: enhance virtqueue access lock asserts"),
the asserts were enhanced to trigger rte_panic functionality, preventing
access to virtqueues without locking. However, this change introduced
an issue where the memory hotplug mechanism, added in the commit
127f9c6f7b78 ("vhost: handle memory hotplug with vDPA devices"),
no longer works. Since it expects for all queues are locked.

During the initialization of a vDPA device, the driver sets the
VIRTIO_DEV_VDPA_CONFIGURED flag, which prevents the
vhost_user_lock_all_queue_pairs function from locking the
virtqueues. This leads to the error: the VIRTIO_DEV_VDPA_CONFIGURED
flag allows the use of the hotplug mechanism, but it fails
because the virtqueues are not locked, while it expects to be locked
for VHOST_USER_SET_MEM_TABLE in the table VHOST_MESSAGE_HANDLERS.

This patch addresses the issue by enhancing the conditional statement
to include a new condition. Specifically, when the device receives the
VHOST_USER_SET_MEM_TABLE request, the virtqueues are locked to update
the basic configurations and hotplug the guest memory.

This fix does not impact access lock when vDPA driver is configured
for other unnecessary message handlers.

Manual memory configuring with "--socket-mem" option allows to avoid
hotplug mechanism using.

Signed-off-by: Danylo Vodopianov <dvo-plv@napatech.com>
---
 lib/vhost/vhost_user.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
index ec950acf97..16d03e1033 100644
--- a/lib/vhost/vhost_user.c
+++ b/lib/vhost/vhost_user.c
@@ -3178,7 +3178,13 @@ vhost_user_msg_handler(int vid, int fd)
 	 * would cause a dead lock.
 	 */
 	if (msg_handler != NULL && msg_handler->lock_all_qps) {
-		if (!(dev->flags & VIRTIO_DEV_VDPA_CONFIGURED)) {
+		/* Lock all queue pairs if the device is not configured for vDPA,
+		 * or if it is configured for vDPA but the request is VHOST_USER_SET_MEM_TABLE.
+		 * This ensures proper queue locking for memory table updates and guest
+		 * memory hotplug.
+		 */
+		if (!(dev->flags & VIRTIO_DEV_VDPA_CONFIGURED) ||
+			request == VHOST_USER_SET_MEM_TABLE) {
 			vhost_user_lock_all_queue_pairs(dev);
 			unlock_required = 1;
 		}
-- 
2.43.5