Support individual region unmap in libvhost-user

When the VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS protocol feature is
enabled, on memory hot-unplug qemu will transmit memory regions to
remove individually using the new message VHOST_USER_REM_MEM_REG
message. With this change, vhost-user backends build with libvhost-user
can now unmap individual memory regions when receiving the
VHOST_USER_REM_MEM_REG message.

Qemu only sends VHOST_USER_REM_MEM_REG messages when the
VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS feature is negotiated, and
support for that feature has not yet been added in libvhost-user, this
new functionality is not yet used.

Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Message-Id: <1588533678-23450-10-git-send-email-raphael.norwitz@nutanix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

2 files changed, 64 insertions, 0 deletions

diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
index d8ee7a23a3..386449b697 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -139,6 +139,7 @@ vu_request_to_string(unsigned int req)
         REQ(VHOST_USER_VRING_KICK),
         REQ(VHOST_USER_GET_MAX_MEM_SLOTS),
         REQ(VHOST_USER_ADD_MEM_REG),
+        REQ(VHOST_USER_REM_MEM_REG),
         REQ(VHOST_USER_MAX),
     };
 #undef REQ
@@ -763,6 +764,66 @@ vu_add_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
     }
 }
 
+static inline bool reg_equal(VuDevRegion *vudev_reg,
+                             VhostUserMemoryRegion *msg_reg)
+{
+    if (vudev_reg->gpa == msg_reg->guest_phys_addr &&
+        vudev_reg->qva == msg_reg->userspace_addr &&
+        vudev_reg->size == msg_reg->memory_size) {
+        return true;
+    }
+
+    return false;
+}
+
+static bool
+vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
+    int i, j;
+    bool found = false;
+    VuDevRegion shadow_regions[VHOST_MEMORY_MAX_NREGIONS] = {};
+    VhostUserMemoryRegion m = vmsg->payload.memreg.region, *msg_region = &m;
+
+    DPRINT("Removing region:\n");
+    DPRINT("    guest_phys_addr: 0x%016"PRIx64"\n",
+           msg_region->guest_phys_addr);
+    DPRINT("    memory_size:     0x%016"PRIx64"\n",
+           msg_region->memory_size);
+    DPRINT("    userspace_addr   0x%016"PRIx64"\n",
+           msg_region->userspace_addr);
+    DPRINT("    mmap_offset      0x%016"PRIx64"\n",
+           msg_region->mmap_offset);
+
+    for (i = 0, j = 0; i < dev->nregions; i++) {
+        if (!reg_equal(&dev->regions[i], msg_region)) {
+            shadow_regions[j].gpa = dev->regions[i].gpa;
+            shadow_regions[j].size = dev->regions[i].size;
+            shadow_regions[j].qva = dev->regions[i].qva;
+            shadow_regions[j].mmap_offset = dev->regions[i].mmap_offset;
+            j++;
+        } else {
+            found = true;
+            VuDevRegion *r = &dev->regions[i];
+            void *m = (void *) (uintptr_t) r->mmap_addr;
+
+            if (m) {
+                munmap(m, r->size + r->mmap_offset);
+            }
+        }
+    }
+
+    if (found) {
+        memcpy(dev->regions, shadow_regions,
+               sizeof(VuDevRegion) * VHOST_MEMORY_MAX_NREGIONS);
+        DPRINT("Successfully removed a region\n");
+        dev->nregions--;
+        vmsg_set_reply_u64(vmsg, 0);
+    } else {
+        vu_panic(dev, "Specified region not found\n");
+    }
+
+    return true;
+}
+
 static bool
 vu_set_mem_table_exec_postcopy(VuDev *dev, VhostUserMsg *vmsg)
 {
@@ -1771,6 +1832,8 @@ vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
         return vu_handle_get_max_memslots(dev, vmsg);
     case VHOST_USER_ADD_MEM_REG:
         return vu_add_mem_reg(dev, vmsg);
+    case VHOST_USER_REM_MEM_REG:
+        return vu_rem_mem_reg(dev, vmsg);
     default:
         vmsg_close_fds(vmsg);
         vu_panic(dev, "Unhandled request: %d", vmsg->request);
diff --git a/contrib/libvhost-user/libvhost-user.h b/contrib/libvhost-user/libvhost-user.h
index 60ef7fd13e..f8439713a8 100644
--- a/contrib/libvhost-user/libvhost-user.h
+++ b/contrib/libvhost-user/libvhost-user.h
@@ -99,6 +99,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_VRING_KICK = 35,
     VHOST_USER_GET_MAX_MEM_SLOTS = 36,
     VHOST_USER_ADD_MEM_REG = 37,
+    VHOST_USER_REM_MEM_REG = 38,
     VHOST_USER_MAX
 } VhostUserRequest;