Re: [PATCH v14 04/11] s390x/sclp: reporting the maximum nested topology entries

[Nina Schoetterl-Glausch <nsg@linux.ibm.com>]

On Thu, 2023-01-05 at 15:53 +0100, Pierre Morel wrote:
> The maximum nested topology entries is used by the guest to know
> how many nested topology are available on the machine.
> 
> Currently, SCLP READ SCP INFO reports MNEST = 0, which is the
> equivalent of reporting the default value of 2.
> Let's use the default SCLP value of 2 and increase this value in the
> future patches implementing higher levels.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>

Reviewed-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
if you address the issues Thomas found with the commit description
and the nits below.

> ---
>  include/hw/s390x/sclp.h | 5 +++--
>  hw/s390x/sclp.c         | 4 ++++
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/include/hw/s390x/sclp.h b/include/hw/s390x/sclp.h
> index 712fd68123..4ce852473c 100644
> --- a/include/hw/s390x/sclp.h
> +++ b/include/hw/s390x/sclp.h
> @@ -112,12 +112,13 @@ typedef struct CPUEntry {
>  } QEMU_PACKED CPUEntry;
>  
>  #define SCLP_READ_SCP_INFO_FIXED_CPU_OFFSET     128
> -#define SCLP_READ_SCP_INFO_MNEST                2
> +#define SCLP_READ_SCP_INFO_MNEST                4
>  typedef struct ReadInfo {
>      SCCBHeader h;
>      uint16_t rnmax;
>      uint8_t rnsize;
> -    uint8_t  _reserved1[16 - 11];       /* 11-15 */
> +    uint8_t  _reserved1[15 - 11];       /* 11-14 */
> +    uint8_t  stsi_parm;                 /* 15-16 */

The numbering here is the same as the one in the arch doc, instead
of the maybe more usual one where the right number is exclusive.
So 15-16 looks like a two byte field, so just do 15 or just drop it.

>      uint16_t entries_cpu;               /* 16-17 */
>      uint16_t offset_cpu;                /* 18-19 */
>      uint8_t  _reserved2[24 - 20];       /* 20-23 */
> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
> index eff74479f4..07e3cb4cac 100644
> --- a/hw/s390x/sclp.c
> +++ b/hw/s390x/sclp.c
> @@ -20,6 +20,7 @@
>  #include "hw/s390x/event-facility.h"
>  #include "hw/s390x/s390-pci-bus.h"
>  #include "hw/s390x/ipl.h"
> +#include "hw/s390x/cpu-topology.h"
>  
>  static inline SCLPDevice *get_sclp_device(void)
>  {
> @@ -125,6 +126,9 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
>  
>      /* CPU information */
>      prepare_cpu_entries(machine, entries_start, &cpu_count);
> +    if (s390_has_topology()) {
> +        read_info->stsi_parm = SCLP_READ_SCP_INFO_MNEST;
> +    }

Maybe move that up a bit, not sure if it belongs under the CPU information section.
I'd leave prepare_cpu_entries and read_info->entries_cpu = adjacent in any case.

>      read_info->entries_cpu = cpu_to_be16(cpu_count);
>      read_info->offset_cpu = cpu_to_be16(offset_cpu);
>      read_info->highest_cpu = cpu_to_be16(machine->smp.max_cpus - 1);