Lift max ram slots limit in libvhost-user

Historically, VMs with vhost-user devices could hot-add memory a maximum
of 8 times. Now that the VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS
protocol feature has been added, VMs with vhost-user backends which
support this new feature can support a configurable number of ram slots
up to the maximum supported by the target platform.

This change adds VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS support for
backends built with libvhost-user, and increases the number of supported
ram slots from 8 to 32.

Memory hot-add, hot-remove and postcopy migration were tested with
the vhost-user-bridge sample.

Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Message-Id: <1588533678-23450-11-git-send-email-raphael.norwitz@nutanix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

contrib/libvhost-user/libvhost-user.c

@@ -269,7 +269,7 @@ have_userfault(void)
 static bool
 vu_message_read(VuDev *dev, int conn_fd, VhostUserMsg *vmsg)
 {
-    char control[CMSG_SPACE(VHOST_MEMORY_MAX_NREGIONS * sizeof(int))] = { };
+    char control[CMSG_SPACE(VHOST_MEMORY_BASELINE_NREGIONS * sizeof(int))] = {};
     struct iovec iov = {
         .iov_base = (char *)vmsg,
         .iov_len = VHOST_USER_HDR_SIZE,
@@ -340,7 +340,7 @@ vu_message_write(VuDev *dev, int conn_fd, VhostUserMsg *vmsg)
 {
     int rc;
     uint8_t *p = (uint8_t *)vmsg;
-    char control[CMSG_SPACE(VHOST_MEMORY_MAX_NREGIONS * sizeof(int))] = { };
+    char control[CMSG_SPACE(VHOST_MEMORY_BASELINE_NREGIONS * sizeof(int))] = {};
     struct iovec iov = {
         .iov_base = (char *)vmsg,
         .iov_len = VHOST_USER_HDR_SIZE,
@@ -353,7 +353,7 @@ vu_message_write(VuDev *dev, int conn_fd, VhostUserMsg *vmsg)
     struct cmsghdr *cmsg;
 
     memset(control, 0, sizeof(control));
-    assert(vmsg->fd_num <= VHOST_MEMORY_MAX_NREGIONS);
+    assert(vmsg->fd_num <= VHOST_MEMORY_BASELINE_NREGIONS);
     if (vmsg->fd_num > 0) {
         size_t fdsize = vmsg->fd_num * sizeof(int);
         msg.msg_controllen = CMSG_SPACE(fdsize);
@@ -780,7 +780,7 @@ static bool
 vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
     int i, j;
     bool found = false;
-    VuDevRegion shadow_regions[VHOST_MEMORY_MAX_NREGIONS] = {};
+    VuDevRegion shadow_regions[VHOST_USER_MAX_RAM_SLOTS] = {};
     VhostUserMemoryRegion m = vmsg->payload.memreg.region, *msg_region = &m;
 
     DPRINT("Removing region:\n");
@@ -813,7 +813,7 @@ vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
 
     if (found) {
         memcpy(dev->regions, shadow_regions,
-               sizeof(VuDevRegion) * VHOST_MEMORY_MAX_NREGIONS);
+               sizeof(VuDevRegion) * VHOST_USER_MAX_RAM_SLOTS);
         DPRINT("Successfully removed a region\n");
         dev->nregions--;
         vmsg_set_reply_u64(vmsg, 0);
@@ -1394,7 +1394,8 @@ vu_get_protocol_features_exec(VuDev *dev, VhostUserMsg *vmsg)
                         1ULL << VHOST_USER_PROTOCOL_F_SLAVE_REQ |
                         1ULL << VHOST_USER_PROTOCOL_F_HOST_NOTIFIER |
                         1ULL << VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD |
-                        1ULL << VHOST_USER_PROTOCOL_F_REPLY_ACK;
+                        1ULL << VHOST_USER_PROTOCOL_F_REPLY_ACK |
+                        1ULL << VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS;
 
     if (have_userfault()) {
         features |= 1ULL << VHOST_USER_PROTOCOL_F_PAGEFAULT;
@@ -1732,14 +1733,14 @@ static bool vu_handle_get_max_memslots(VuDev *dev, VhostUserMsg *vmsg)
 {
     vmsg->flags = VHOST_USER_REPLY_MASK | VHOST_USER_VERSION;
     vmsg->size  = sizeof(vmsg->payload.u64);
-    vmsg->payload.u64 = VHOST_MEMORY_MAX_NREGIONS;
+    vmsg->payload.u64 = VHOST_USER_MAX_RAM_SLOTS;
     vmsg->fd_num = 0;
 
     if (!vu_message_write(dev, dev->sock, vmsg)) {
         vu_panic(dev, "Failed to send max ram slots: %s\n", strerror(errno));
     }
 
-    DPRINT("u64: 0x%016"PRIx64"\n", (uint64_t) VHOST_MEMORY_MAX_NREGIONS);
+    DPRINT("u64: 0x%016"PRIx64"\n", (uint64_t) VHOST_USER_MAX_RAM_SLOTS);
 
     return false;
 }

contrib/libvhost-user/libvhost-user.h

@@ -28,7 +28,13 @@
 
 #define VIRTQUEUE_MAX_SIZE 1024
 
-#define VHOST_MEMORY_MAX_NREGIONS 8
+#define VHOST_MEMORY_BASELINE_NREGIONS 8
+
+/*
+ * Set a reasonable maximum number of ram slots, which will be supported by
+ * any architecture.
+ */
+#define VHOST_USER_MAX_RAM_SLOTS 32
 
 typedef enum VhostSetConfigType {
     VHOST_SET_CONFIG_TYPE_MASTER = 0,
@@ -55,6 +61,7 @@ enum VhostUserProtocolFeature {
     VHOST_USER_PROTOCOL_F_HOST_NOTIFIER = 11,
     VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD = 12,
     VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS = 14,
+    VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS = 15,
 
     VHOST_USER_PROTOCOL_F_MAX
 };
@@ -123,7 +130,7 @@ typedef struct VhostUserMemoryRegion {
 typedef struct VhostUserMemory {
     uint32_t nregions;
     uint32_t padding;
-    VhostUserMemoryRegion regions[VHOST_MEMORY_MAX_NREGIONS];
+    VhostUserMemoryRegion regions[VHOST_MEMORY_BASELINE_NREGIONS];
 } VhostUserMemory;
 
 typedef struct VhostUserMemRegMsg {
@@ -190,7 +197,7 @@ typedef struct VhostUserMsg {
         VhostUserInflight inflight;
     } payload;
 
-    int fds[VHOST_MEMORY_MAX_NREGIONS];
+    int fds[VHOST_MEMORY_BASELINE_NREGIONS];
     int fd_num;
     uint8_t *data;
 } VU_PACKED VhostUserMsg;
@@ -368,7 +375,7 @@ typedef struct VuDevInflightInfo {
 struct VuDev {
     int sock;
     uint32_t nregions;
-    VuDevRegion regions[VHOST_MEMORY_MAX_NREGIONS];
+    VuDevRegion regions[VHOST_USER_MAX_RAM_SLOTS];
     VuVirtq *vq;
     VuDevInflightInfo inflight_info;
     int log_call_fd;