target/s390x/kvm/pv: Provide some more useful information if decryption fails

It's a common scenario to copy guest images from one host to another
to run the guest on the other machine. This (of course) does not work
with "secure execution" guests since they are encrypted with one certain
host key. However, if you still (accidentally) do it, you only get a
very user-unfriendly error message that looks like this:

 qemu-system-s390x: KVM PV command 2 (KVM_PV_SET_SEC_PARMS) failed:
  header rc 108 rrc 5 IOCTL rc: -22

Let's provide at least a somewhat nicer hint to the users so that they
are able to figure out what might have gone wrong.

Buglink: https://issues.redhat.com/browse/RHEL-18212
Message-ID: <20240110142916.850605-1-thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

2 files changed, 23 insertions, 7 deletions

diff --git a/target/s390x/kvm/pv.c b/target/s390x/kvm/pv.c
index 6a69be7..7ca7fae 100644
--- a/target/s390x/kvm/pv.c
+++ b/target/s390x/kvm/pv.c
@@ -29,7 +29,8 @@ static bool info_valid;
 static struct kvm_s390_pv_info_vm info_vm;
 static struct kvm_s390_pv_info_dump info_dump;
 
-static int __s390_pv_cmd(uint32_t cmd, const char *cmdname, void *data)
+static int __s390_pv_cmd(uint32_t cmd, const char *cmdname, void *data,
+                         int *pvrc)
 {
     struct kvm_pv_cmd pv_cmd = {
         .cmd = cmd,
@@ -46,6 +47,9 @@ static int __s390_pv_cmd(uint32_t cmd, const char *cmdname, void *data)
                      "IOCTL rc: %d", cmd, cmdname, pv_cmd.rc, pv_cmd.rrc,
                      rc);
     }
+    if (pvrc) {
+        *pvrc = pv_cmd.rc;
+    }
     return rc;
 }
 
@@ -53,12 +57,13 @@ static int __s390_pv_cmd(uint32_t cmd, const char *cmdname, void *data)
  * This macro lets us pass the command as a string to the function so
  * we can print it on an error.
  */
-#define s390_pv_cmd(cmd, data) __s390_pv_cmd(cmd, #cmd, data)
+#define s390_pv_cmd(cmd, data) __s390_pv_cmd(cmd, #cmd, data, NULL)
+#define s390_pv_cmd_pvrc(cmd, data, pvrc) __s390_pv_cmd(cmd, #cmd, data, pvrc)
 #define s390_pv_cmd_exit(cmd, data)    \
 {                                      \
     int rc;                            \
                                        \
-    rc = __s390_pv_cmd(cmd, #cmd, data);\
+    rc = __s390_pv_cmd(cmd, #cmd, data, NULL); \
     if (rc) {                          \
         exit(1);                       \
     }                                  \
@@ -142,14 +147,24 @@ bool s390_pv_vm_try_disable_async(S390CcwMachineState *ms)
     return true;
 }
 
-int s390_pv_set_sec_parms(uint64_t origin, uint64_t length)
+int s390_pv_set_sec_parms(uint64_t origin, uint64_t length, Error **errp)
 {
+    int ret, pvrc;
     struct kvm_s390_pv_sec_parm args = {
         .origin = origin,
         .length = length,
     };
 
-    return s390_pv_cmd(KVM_PV_SET_SEC_PARMS, &args);
+    ret = s390_pv_cmd_pvrc(KVM_PV_SET_SEC_PARMS, &args, &pvrc);
+    if (ret) {
+        error_setg(errp, "Failed to set secure execution parameters");
+        if (pvrc == 0x108) {
+            error_append_hint(errp, "Please check whether the image is "
+                                    "correctly encrypted for this host\n");
+        }
+    }
+
+    return ret;
 }
 
 /*
diff --git a/target/s390x/kvm/pv.h b/target/s390x/kvm/pv.h
index 7b935e2..5877d28 100644
--- a/target/s390x/kvm/pv.h
+++ b/target/s390x/kvm/pv.h
@@ -42,7 +42,7 @@ int s390_pv_query_info(void);
 int s390_pv_vm_enable(void);
 void s390_pv_vm_disable(void);
 bool s390_pv_vm_try_disable_async(S390CcwMachineState *ms);
-int s390_pv_set_sec_parms(uint64_t origin, uint64_t length);
+int s390_pv_set_sec_parms(uint64_t origin, uint64_t length, Error **errp);
 int s390_pv_unpack(uint64_t addr, uint64_t size, uint64_t tweak);
 void s390_pv_prep_reset(void);
 int s390_pv_verify(void);
@@ -62,7 +62,8 @@ static inline int s390_pv_query_info(void) { return 0; }
 static inline int s390_pv_vm_enable(void) { return 0; }
 static inline void s390_pv_vm_disable(void) {}
 static inline bool s390_pv_vm_try_disable_async(S390CcwMachineState *ms) { return false; }
-static inline int s390_pv_set_sec_parms(uint64_t origin, uint64_t length) { return 0; }
+static inline int s390_pv_set_sec_parms(uint64_t origin, uint64_t length,
+                                        Error **errp) { return 0; }
 static inline int s390_pv_unpack(uint64_t addr, uint64_t size, uint64_t tweak) { return 0; }
 static inline void s390_pv_prep_reset(void) {}
 static inline int s390_pv_verify(void) { return 0; }