Re: [PATCH v10 2/9] s390x/cpu topology: reporting the CPU topology to the guest

[Pierre Morel]

On 10/27/22 22:42, Janis Schoetterl-Glausch wrote:
> On Wed, 2022-10-12 at 18:21 +0200, Pierre Morel wrote:
> > The guest can use the STSI instruction to get a buffer filled
> > with the CPU topology description.
> >
> > Let us implement the STSI instruction for the basis CPU topology
> > level, level 2.
> >
> > Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> > ---
> >   include/hw/s390x/cpu-topology.h |   3 +
> >   target/s390x/cpu.h              |  48 ++++++++++++++
> >   hw/s390x/cpu-topology.c         |   8 ++-
> >   target/s390x/cpu_topology.c     | 109 ++++++++++++++++++++++++++++++++
> >   target/s390x/kvm/kvm.c          |   6 +-
> >   target/s390x/meson.build        |   1 +
> >   6 files changed, 172 insertions(+), 3 deletions(-)
> >   create mode 100644 target/s390x/cpu_topology.c
> >
> > diff --git a/include/hw/s390x/cpu-topology.h b/include/hw/s390x/cpu-topology.h
> > index 66c171d0bc..61c11db017 100644
> > --- a/include/hw/s390x/cpu-topology.h
> > +++ b/include/hw/s390x/cpu-topology.h
> > @@ -13,6 +13,8 @@
> >   #include "hw/qdev-core.h"
> >   #include "qom/object.h"
> >   
> > +#define S390_TOPOLOGY_POLARITY_H  0x00
> > +
> >   typedef struct S390TopoContainer {
> >       int active_count;
> >   } S390TopoContainer;
> > @@ -29,6 +31,7 @@ struct S390Topology {
> >       S390TopoContainer *socket;
> >       S390TopoTLE *tle;
> >       MachineState *ms;
> > +    QemuMutex topo_mutex;
> >   };
> >   
> >   #define TYPE_S390_CPU_TOPOLOGY "s390-topology"
> > diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
> > index 7d6d01325b..d604aa9c78 100644
> > --- a/target/s390x/cpu.h
> > +++ b/target/s390x/cpu.h
> [...]
> > +
> > +/* Maxi size of a SYSIB structure is when all CPU are alone in a container */
>
> Max or Maximum.
>
> > +#define S390_TOPOLOGY_SYSIB_SIZE (sizeof(SysIB_151x) +                         
> > \
> > +                                  S390_MAX_CPUS * (sizeof(SysIBTl_container) + 
> > \
> > +                                                   sizeof(SysIBTl_cpu)))
>
> Currently this is 16+248*3*8 == 5968 and will grow with books, drawer support to
> 16+248*5*8 == 9936 ...
>
> [...]
> > +
> > +void insert_stsi_15_1_x(S390CPU *cpu, int sel2, __u64 addr, uint8_t ar)
> > +{
> > +    uint64_t page[S390_TOPOLOGY_SYSIB_SIZE / sizeof(uint64_t)] = {};
>
> ... so calling this page is a bit misleading. Also why not make it a char[]?
> And maybe use a union for type punning.

OK, what about:

    union {
        char place_holder[S390_TOPOLOGY_SYSIB_SIZE];
        SysIB_151x sysib;
    } buffer QEMU_ALIGNED(8);


> > +    SysIB_151x *sysib = (SysIB_151x *) page;
> > +    int len;
> > +
> > +    if (s390_is_pv() || !s390_has_topology() ||
> > +        sel2 < 2 || sel2 > S390_TOPOLOGY_MAX_MNEST) {
> > +        setcc(cpu, 3);
> > +        return;
> > +    }
> > +
> > +    len = setup_stsi(sysib, sel2);
>
> This should now be memory safe, but might be larger than 4k,
> the maximum size of the SYSIB. I guess you want to set cc code 3
> in this case and return.

I do not find why the SYSIB can not be larger than 4k.
Can you point me to this restriction?


Regards,
Pierre

--
Pierre Morel
IBM Lab Boeblingen