Re: [PATCH] target/s390x/kvm/pv: Provide some more useful information if decryption fails

["Cédric Le Goater" <clegoate@redhat.com>]

On 1/9/24 15:30, Thomas Huth wrote:
> 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 exection" 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
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>   target/s390x/kvm/pv.c | 20 ++++++++++++++++----
>   1 file changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/target/s390x/kvm/pv.c b/target/s390x/kvm/pv.c
> index 6a69be7e5c..2833a255fa 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);                       \
>       }                                  \
> @@ -144,12 +149,19 @@ bool s390_pv_vm_try_disable_async(S390CcwMachineState *ms)
>   
>   int s390_pv_set_sec_parms(uint64_t origin, uint64_t length)
>   {
> +    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 && pvrc == 0x108) {

why do we need to test for 0x108 also ? if this sub error code is important,
adding a define would be a plus.

> +        error_report("Can't set secure parameters, please check whether "
> +                     "the image is correctly encrypted for this host");
The error reporting in s390x_machine_protect() could be improved.

I would add a 'Error *' argument to the routines called by
s390x_machine_protect() and report the error in s390x_machine_protect()
or above. s390_machine_protect() return value is ignored also, could be
replaced by a bool.

Thanks,

C.



> +    }
> +
> +    return ret;
>   }
>   
>   /*