docs(amdsev): clarify control socket channel

Author: kariy

misc/AMDSEV/README.md

@@ -101,6 +101,34 @@ qemu-system-x86_64 \
     ..
 ```
 
+### Start Katana via Control Channel
+
+In the QEMU example above, this line defines the host-side control channel endpoint:
+
+```sh
+-chardev socket,id=katanactl,path=/tmp/katana-control.sock,server=on,wait=off
+```
+
+The `path=/tmp/katana-control.sock` value is the Unix socket file on the host.  
+That socket is connected to the guest virtio-serial port:
+
+```sh
+-device virtserialport,chardev=katanactl,name=org.katana.control.0
+```
+
+So writes to that Unix socket become control commands inside the VM (`start`, `status`).
+
+Example:
+
+```sh
+# Start Katana with comma-separated CLI args
+printf 'start --http.addr,0.0.0.0,--http.port,5050,--tee.provider,sev-snp\n' \
+  | socat - UNIX-CONNECT:/tmp/katana-control.sock
+
+# Check launcher status
+printf 'status\n' | socat - UNIX-CONNECT:/tmp/katana-control.sock
+```
+
 ## Running the VM
 
 The `start-vm.sh` script provides an easy way to launch a TEE VM with SEV-SNP enabled:
@@ -124,30 +152,6 @@ The script:
 - Forwards RPC port 5050 to host port 15051
 - Outputs serial log to a temp file and follows it
 
-### Start Katana via Control Channel
-
-To start Katana manually over the control channel:
-
-```sh
-# 1) Boot VM without auto-starting Katana
-sudo ./misc/AMDSEV/start-vm.sh --no-start
-
-# 2) Use the control socket printed by start-vm.sh (example path below)
-CONTROL_SOCKET=/tmp/katana-tee-vm-control.12345.sock
-
-# 3) Start Katana with comma-separated CLI args
-printf 'start --http.addr,0.0.0.0,--http.port,5050,--tee.provider,sev-snp\n' \
-  | socat - UNIX-CONNECT:"$CONTROL_SOCKET"
-
-# 4) Check launcher status
-printf 'status\n' | socat - UNIX-CONNECT:"$CONTROL_SOCKET"
-```
-
-Control responses:
-- `ok started pid=...` means Katana was launched.
-- `running pid=...` means Katana is still running.
-- `stopped exit=...` means Katana is not running.
-
 ### Launch Measurement Verification
 
 To verify a TEE VM's integrity, compute the expected launch measurement using `snp-digest`: