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

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Jan 09, 2024 at 03:30:38PM +0100, 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:

Not a comment on the patch, but my own interest how/where does the
disk image encryption/decryption happen ?  Is that in guest kernel
context, and any info on what format the encryption uses ?

> 
>  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) {
> +        error_report("Can't set secure parameters, please check whether "
> +                     "the image is correctly encrypted for this host");
> +    }
> +
> +    return ret;
>  }
>  
>  /*
> -- 
> 2.43.0
> 
> 

With regards,
Daniel
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