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

[Pierre Morel <pmorel@linux.ibm.com>]

On 10/27/22 10:12, Thomas Huth wrote:
> On 12/10/2022 18.21, 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
>> @@ -565,6 +565,52 @@ typedef union SysIB {
>>   } SysIB;
>>   QEMU_BUILD_BUG_ON(sizeof(SysIB) != 4096);
>> +/* CPU type Topology List Entry */
>> +typedef struct SysIBTl_cpu {
>> +        uint8_t nl;
>> +        uint8_t reserved0[3];
>> +        uint8_t reserved1:5;
>> +        uint8_t dedicated:1;
>> +        uint8_t polarity:2;
>> +        uint8_t type;
>> +        uint16_t origin;
>> +        uint64_t mask;
>> +} QEMU_PACKED QEMU_ALIGNED(8) SysIBTl_cpu;
>> +QEMU_BUILD_BUG_ON(sizeof(SysIBTl_cpu) != 16);
>> +
>> +/* Container type Topology List Entry */
>> +typedef struct SysIBTl_container {
>> +        uint8_t nl;
>> +        uint8_t reserved[6];
>> +        uint8_t id;
>> +} QEMU_PACKED QEMU_ALIGNED(8) SysIBTl_container;
>> +QEMU_BUILD_BUG_ON(sizeof(SysIBTl_container) != 8);
>> +
>> +#define TOPOLOGY_NR_MAG  6
>> +#define TOPOLOGY_NR_MAG6 0
>> +#define TOPOLOGY_NR_MAG5 1
>> +#define TOPOLOGY_NR_MAG4 2
>> +#define TOPOLOGY_NR_MAG3 3
>> +#define TOPOLOGY_NR_MAG2 4
>> +#define TOPOLOGY_NR_MAG1 5
>> +/* Configuration topology */
>> +typedef struct SysIB_151x {
>> +    uint8_t  reserved0[2];
>> +    uint16_t length;
>> +    uint8_t  mag[TOPOLOGY_NR_MAG];
>> +    uint8_t  reserved1;
>> +    uint8_t  mnest;
>> +    uint32_t reserved2;
>> +    char tle[0];
>> +} QEMU_PACKED QEMU_ALIGNED(8) SysIB_151x;
>> +QEMU_BUILD_BUG_ON(sizeof(SysIB_151x) != 16);
>> +
>> +/* Maxi size of a SYSIB structure is when all CPU are alone in a 
>> container */
>> +#define S390_TOPOLOGY_SYSIB_SIZE (sizeof(SysIB_151x) 
>> +                         \
>> +                                  S390_MAX_CPUS * 
>> (sizeof(SysIBTl_container) + \
>> +                                                   sizeof(SysIBTl_cpu)))
>> +
>> +
>>   /* MMU defines */
>>   #define ASCE_ORIGIN           (~0xfffULL) /* segment table 
>> origin             */
>>   #define ASCE_SUBSPACE         0x200       /* subspace group 
>> control           */
>> @@ -843,4 +889,6 @@ S390CPU *s390_cpu_addr2state(uint16_t cpu_addr);
>>   #include "exec/cpu-all.h"
>> +void insert_stsi_15_1_x(S390CPU *cpu, int sel2, __u64 addr, uint8_t ar);
>> +
>>   #endif
>> diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
>> index 42b22a1831..c73cebfe6f 100644
>> --- a/hw/s390x/cpu-topology.c
>> +++ b/hw/s390x/cpu-topology.c
>> @@ -54,8 +54,6 @@ void s390_topology_new_cpu(int core_id)
>>           return;
>>       }
>> -    socket_id = core_id / topo->cpus;
>> -
>>       /*
>>        * At the core level, each CPU is represented by a bit in a 64bit
>>        * unsigned long which represent the presence of a CPU.
>> @@ -76,8 +74,13 @@ void s390_topology_new_cpu(int core_id)
>>       bit %= 64;
>>       bit = 63 - bit;
>> +    qemu_mutex_lock(&topo->topo_mutex);
>> +
>> +    socket_id = core_id / topo->cpus;
>>       topo->socket[socket_id].active_count++;
>>       set_bit(bit, &topo->tle[socket_id].mask[origin]);
>> +
>> +    qemu_mutex_unlock(&topo->topo_mutex);
>>   }
>>   /**
>> @@ -101,6 +104,7 @@ static void s390_topology_realize(DeviceState 
>> *dev, Error **errp)
>>       topo->tle = g_new0(S390TopoTLE, ms->smp.max_cpus);
>>       topo->ms = ms;
>> +    qemu_mutex_init(&topo->topo_mutex);
>>   }
>>   /**
>> diff --git a/target/s390x/cpu_topology.c b/target/s390x/cpu_topology.c
>> new file mode 100644
>> index 0000000000..df86a98f23
>> --- /dev/null
>> +++ b/target/s390x/cpu_topology.c
>> @@ -0,0 +1,109 @@
>> +/*
>> + * QEMU S390x CPU Topology
>> + *
>> + * Copyright IBM Corp. 2022
>> + * Author(s): Pierre Morel <pmorel@linux.ibm.com>
>> + *
>> + * This work is licensed under the terms of the GNU GPL, version 2 or 
>> (at
>> + * your option) any later version. See the COPYING file in the top-level
>> + * directory.
>> + */
>> +#include "qemu/osdep.h"
>> +#include "cpu.h"
>> +#include "hw/s390x/pv.h"
>> +#include "hw/sysbus.h"
>> +#include "hw/s390x/cpu-topology.h"
>> +#include "hw/s390x/sclp.h"
>> +
>> +#define S390_TOPOLOGY_MAX_STSI_SIZE (S390_MAX_CPUS *              \
>> +                                     (sizeof(SysIB_151x) +        \
>> +                                      sizeof(SysIBTl_container) + \
>> +                                      sizeof(SysIBTl_cpu)))
>> +
>> +static char *fill_container(char *p, int level, int id)
>> +{
>> +    SysIBTl_container *tle = (SysIBTl_container *)p;
>> +
>> +    tle->nl = level;
>> +    tle->id = id;
>> +    return p + sizeof(*tle);
>> +}
>> +
>> +static char *fill_tle_cpu(char *p, uint64_t mask, int origin)
>> +{
>> +    SysIBTl_cpu *tle = (SysIBTl_cpu *)p;
>> +
>> +    tle->nl = 0;
>> +    tle->dedicated = 1;
>> +    tle->polarity = S390_TOPOLOGY_POLARITY_H;
>> +    tle->type = S390_TOPOLOGY_CPU_IFL;
>> +    tle->origin = cpu_to_be64(origin * 64);
>> +    tle->mask = cpu_to_be64(mask);
>> +    return p + sizeof(*tle);
>> +}
>> +
>> +static char *s390_top_set_level2(S390Topology *topo, char *p)
>> +{
>> +    MachineState *ms = topo->ms;
>> +    int i, origin;
>> +
>> +    for (i = 0; i < ms->smp.sockets; i++) {
>> +        if (!topo->socket[i].active_count) {
>> +            continue;
>> +        }
>> +        p = fill_container(p, 1, i);
>> +        for (origin = 0; origin < S390_TOPOLOGY_MAX_ORIGIN; origin++) {
>> +            uint64_t mask = 0L;
>> +
>> +            mask = topo->tle[i].mask[origin];
>> +            if (mask) {
>> +                p = fill_tle_cpu(p, mask, origin);
>> +            }
>> +        }
>> +    }
>> +    return p;
>> +}
>> +
>> +static int setup_stsi(SysIB_151x *sysib, int level)
>> +{
>> +    S390Topology *topo = s390_get_topology();
>> +    MachineState *ms = topo->ms;
>> +    char *p = sysib->tle;
>> +
>> +    qemu_mutex_lock(&topo->topo_mutex);
>> +
>> +    sysib->mnest = level;
>> +    switch (level) {
>> +    case 2:
>> +        sysib->mag[TOPOLOGY_NR_MAG2] = ms->smp.sockets;
>> +        sysib->mag[TOPOLOGY_NR_MAG1] = topo->cpus;
>> +        p = s390_top_set_level2(topo, p);
>> +        break;
>> +    }
>> +
>> +    qemu_mutex_unlock(&topo->topo_mutex);
> 
> Could you elaborate (maybe in the commit description) why you need a 
> separate mutex here? ... I'd expect that all the STSI stuff is run with 
> the BQL (big qemu lock) held (see kvm_arch_handle_exit()), so yet 
> another mutex sounds rendundant to me here?
> 
>   Thomas
> 

Right and since BQL is hold for the hotplug, there is no need.
Thanks.

Pierre

-- 
Pierre Morel
IBM Lab Boeblingen