Re: [PATCH v3 5/8] s390/sclp: use cpu offset to locate cpu entries

[Janosch Frank]

On 6/19/20 12:22 AM, Collin Walling wrote:
> The start of the CPU entry region in the Read SCP Info response data is
> denoted by the offset_cpu field. As such, QEMU needs to begin creating
> entries at this address. Note that the length of the Read SCP Info data
> (data_len) denotes the same value as the cpu offset.
> 
> This is in preparation of when Read SCP Info inevitably introduces new
> bytes that push the start of the CPUEntry field further away.
> 
> Read CPU Info is unlikely to ever change, so let's not bother
> accounting for the offset there.
> 
> Signed-off-by: Collin Walling <walling@linux.ibm.com>
> Reviewed-by: Thomas Huth <thuth@redhat.com>

Reviewed-by: Janosch Frank <frankja@linux.ibm.com>

> ---
>  hw/s390x/sclp.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
> index 772b7b3b01..0dfbe6e5ec 100644
> --- a/hw/s390x/sclp.c
> +++ b/hw/s390x/sclp.c
> @@ -113,13 +113,14 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
>      int rnsize, rnmax;
>      IplParameterBlock *ipib = s390_ipl_get_iplb();
>      int data_len = get_read_scp_info_data_len();
> +    CPUEntry *entries_start = (void *)sccb + data_len;
>  
>      if (!sccb_sufficient_len(sccb, machine->possible_cpus->len, data_len)) {
>          return;
>      }
>  
>      /* CPU information */
> -    prepare_cpu_entries(machine, read_info->entries, &cpu_count);
> +    prepare_cpu_entries(machine, entries_start, &cpu_count);
>      read_info->entries_cpu = cpu_to_be16(cpu_count);
>      read_info->offset_cpu = cpu_to_be16(data_len);
>      read_info->highest_cpu = cpu_to_be16(machine->smp.max_cpus - 1);
>

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