[dpdk-dev] [PATCH] vhost: fix segfault as handle set_mem_table message

[Jianfeng Tan]

In a running VM, operations (like device attach/detach) will
trigger the QEMU to resend set_mem_table to vhost-user backend.

DPDK vhost-user handles this message rudely by unmap all existing
regions and map new ones. This might lead to segfault if there
is pmd thread just trying to touch those unmapped memory regions.

But for most cases, except VM memory hotplug, QEMU still sends the
set_mem_table message even the memory regions are not changed as
QEMU vhost-user filters out those not backed by file (fd > 0).

To fix this case, we add a check in the handler to see if the
memory regions are really changed; if not, we just keep old memory
regions.

Fixes: 8f972312b8f4 ("vhost: support vhost-user")

CC: stable at dpdk.org

CC: Yuanhan Liu <yliu at fridaylinux.org>
CC: Maxime Coquelin <maxime.coquelin at redhat.com>

Reported-by: Yang Zhang <zy107165 at alibaba-inc.com>
Reported-by: Xin Long <longxin.xl at alibaba-inc.com>
Signed-off-by: Yi Yang <yi.y.yang at intel.com>
Signed-off-by: Jianfeng Tan <jianfeng.tan at intel.com>
---
 lib/librte_vhost/vhost_user.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index f4c7ce4..2291929 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -573,6 +573,29 @@ dump_guest_pages(struct virtio_net *dev)
 #define dump_guest_pages(dev)
 #endif
 
+static bool vhost_memory_changed(struct VhostUserMemory *new,
+				 struct rte_vhost_memory *old)
+{
+	uint32_t i;
+
+	if (new->nregions != old->nregions)
+		return true;
+
+	for (i = 0; i < new->nregions; ++i) {
+		VhostUserMemoryRegion *new_r = &new->regions[i];
+		struct rte_vhost_mem_region *old_r = &old->regions[i];
+
+		if (new_r->guest_phys_addr != old_r->guest_phys_addr)
+			return true;
+		if (new_r->memory_size != old_r->size)
+			return true;
+		if (new_r->userspace_addr != old_r->guest_user_addr)
+			return true;
+	}
+
+	return false;
+}
+
 static int
 vhost_user_set_mem_table(struct virtio_net *dev, struct VhostUserMsg *pmsg)
 {
@@ -585,6 +608,16 @@ vhost_user_set_mem_table(struct virtio_net *dev, struct VhostUserMsg *pmsg)
 	uint32_t i;
 	int fd;
 
+	if (dev->mem && !vhost_memory_changed(&memory, dev->mem)) {
+		RTE_LOG(INFO, VHOST_CONFIG,
+			"(%d) memory regions not changed\n", dev->vid);
+
+		for (i = 0; i < memory.nregions; i++)
+			close(pmsg->fds[i]);
+
+		return 0;
+	}
+
 	if (dev->mem) {
 		free_mem_region(dev);
 		rte_free(dev->mem);
-- 
2.7.4