Re: [Qemu-devel] [PATCH v2 2/3] s390: cpu feature for diagnose 318 andlimit max VCPUs to 247

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 06.12.2018 23:24, Collin Walling wrote:
> Diagnose 318 is a new z14.2 CPU feature. Since we are able to emulate
> it entirely via KVM, we can add guest support for earlier models. A
> new CPU feature for diagnose 318 (shortened to diag318) will be made
> available to guests starting with the zEC12-full CPU model.
> 
> The z14.2 adds a new read SCP info byte (let's call it byte 134) to
> detect the availability of diag318. Because of this, we have room for
> one less VCPU and thus limit the max VPUs supported in a configuration
> to 247 (down from 248).
> 
> Signed-off-by: Collin Walling <walling@linux.ibm.com>.
> ---
>  hw/s390x/sclp.c                 | 2 ++
>  include/hw/s390x/sclp.h         | 2 ++
>  target/s390x/cpu.h              | 2 +-
>  target/s390x/cpu_features.c     | 3 +++
>  target/s390x/cpu_features.h     | 1 +
>  target/s390x/cpu_features_def.h | 3 +++
>  target/s390x/gen-features.c     | 1 +
>  target/s390x/kvm.c              | 1 +
>  8 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
> index 4510a80..183c627 100644
> --- a/hw/s390x/sclp.c
> +++ b/hw/s390x/sclp.c
> @@ -73,6 +73,8 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
>                           read_info->conf_char);
>      s390_get_feat_block(S390_FEAT_TYPE_SCLP_CONF_CHAR_EXT,
>                           read_info->conf_char_ext);
> +    /* Read Info byte 134 */
> +    s390_get_feat_block(S390_FEAT_TYPE_SCLP_BYTE_134, read_info->byte_134);
>  
>      read_info->facilities = cpu_to_be64(SCLP_HAS_CPU_INFO |
>                                          SCLP_HAS_IOA_RECONFIG);
> diff --git a/include/hw/s390x/sclp.h b/include/hw/s390x/sclp.h
> index f9db243..eb12ba2 100644
> --- a/include/hw/s390x/sclp.h
> +++ b/include/hw/s390x/sclp.h
> @@ -133,6 +133,8 @@ typedef struct ReadInfo {
>      uint16_t highest_cpu;
>      uint8_t  _reserved5[124 - 122];     /* 122-123 */
>      uint32_t hmfai;
> +    uint8_t  _reserved7[134 - 128];     /* 128-133 */
> +    uint8_t  byte_134[1];
>      struct CPUEntry entries[0];
>  } QEMU_PACKED ReadInfo;
 
The size must be a multiple of 16. Can you add a reserved field to fill up
until 144?