Re: [PATCH] target/s390x: Make container ids in SysIB_15x 1-based

[Gautam Gala <ggala@linux.ibm.com>]

On Mon, May 11, 2026 at 03:49:09PM +0200, Alexandra Winter wrote:
> The Container Id in a container-type TLE of SysIB_15x is defined as 8-bit
> unsigned nonzero integer. Make stsi fc 15 emulation architecture compliant,
> by starting the container ids at 1 for the lowest numbered container.
> 
> The qemu misbehaviour without this patch becomes obvious due to a recently
> proposed kernel fix. Older linux kernels pass the container ids from stsi
> fc15 unchanged to sysfs, i.e. starting at 1 on s390 hardware. This resulted
> in off-by-one values when compared to the values from HMC. A Linux kernel
> fix is being proposed to correct the sysfs topology ids by -1, so they
> start at 0, e.g. when displayed by 'lscpu -ye'. In case a KVM guest with a
> fixed kernel runs on a host with a qemu without this fix, this can result
> in container ids erroneously being shown as 255.
> Example (Fixed guest on unfixed qemu):
> $ lscpu -ye
> CPU NODE DRAWER BOOK SOCKET CORE L1d:L1i:L2 ONLINE CONFIGURED POLARIZATION ADDRESS
>   0    0    255  255    255    0 0:0:0         yes yes        vert-medium  0
>   1    0    255  255      0    1 1:1:1         yes yes        vert-medium  1
> After this fix:
> $ lscpu -ye
> CPU NODE DRAWER BOOK SOCKET CORE L1d:L1i:L2 ONLINE CONFIGURED POLARIZATION ADDRESS
>   0    0      0    0      0    0 0:0:0         yes yes        vert-medium  0
>   1    0      0    0      1    1 1:1:1         yes yes        vert-medium  1
> 
> Fixes: f4f54b582f ("target/s390x/cpu topology: handle STSI(15) and build the SYSIB")
> Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
> ---
>  target/s390x/kvm/stsi-topology.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/target/s390x/kvm/stsi-topology.c b/target/s390x/kvm/stsi-topology.c
> index 301d41b68d..afd00da0e6 100644
> --- a/target/s390x/kvm/stsi-topology.c
> +++ b/target/s390x/kvm/stsi-topology.c
> @@ -90,9 +90,9 @@ static int stsi_topology_fill_sysib(S390TopologyList *topology_list,
>      int last_drawer = -1;
>      int last_book = -1;
>      int last_socket = -1;
> -    int drawer_id = 0;
> -    int book_id = 0;
> -    int socket_id = 0;
> +    int drawer_id = 1;
> +    int book_id = 1;
> +    int socket_id = 1;
>      int n = sizeof(SysIB_151x);
>  
>      QTAILQ_FOREACH(entry, topology_list, next) {
> @@ -103,12 +103,12 @@ static int stsi_topology_fill_sysib(S390TopologyList *topology_list,
>          if (level > 3 && drawer_change) {
>              SYSIB_GUARD(n, sizeof(SYSIBContainerListEntry));
>              p = fill_container(p, 3, drawer_id++);
> -            book_id = 0;
> +            book_id = 1;
>          }
>          if (level > 2 && book_change) {
>              SYSIB_GUARD(n, sizeof(SYSIBContainerListEntry));
>              p = fill_container(p, 2, book_id++);
> -            socket_id = 0;
> +            socket_id = 1;
>          }
>          if (socket_change) {
>              SYSIB_GUARD(n, sizeof(SYSIBContainerListEntry));
> -- 
> 2.39.5 (Apple Git-154)
>
Thanks, this looks correct.

Reviewed-by: Gautam Gala <ggala@linux.ibm.com>