Re: [PATCH v15 08/11] qapi/s390x/cpu topology: x-set-cpu-topology monitor command

[Thomas Huth <thuth@redhat.com>]

On 01/02/2023 14.20, Pierre Morel wrote:
> The modification of the CPU attributes are done through a monitor
> command.
> 
> It allows to move the core inside the topology tree to optimise

I'm not a native speaker, but "optimize" is more common, I think?

> the cache usage in the case the host's hypervisor previously
> moved the CPU.
> 
> The same command allows to modify the CPU attributes modifiers
> like polarization entitlement and the dedicated attribute to notify
> the guest if the host admin modified scheduling or dedication of a vCPU.
> 
> With this knowledge the guest has the possibility to optimize the
> usage of the vCPUs.
> 
> The command is made experimental for the moment.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>   qapi/machine-target.json | 29 +++++++++++++
>   include/monitor/hmp.h    |  1 +
>   hw/s390x/cpu-topology.c  | 88 ++++++++++++++++++++++++++++++++++++++++
>   hmp-commands.hx          | 16 ++++++++
>   4 files changed, 134 insertions(+)
> 
> diff --git a/qapi/machine-target.json b/qapi/machine-target.json
> index 2e267fa458..58df0f5061 100644
> --- a/qapi/machine-target.json
> +++ b/qapi/machine-target.json
> @@ -342,3 +342,32 @@
>                      'TARGET_S390X',
>                      'TARGET_MIPS',
>                      'TARGET_LOONGARCH64' ] } }
> +
> +##
> +# @x-set-cpu-topology:
> +#
> +# @core: the vCPU ID to be moved
> +# @socket: the destination socket where to move the vCPU
> +# @book: the destination book where to move the vCPU
> +# @drawer: the destination drawer where to move the vCPU
> +# @polarity: optional polarity, default is last polarity set by the guest

Hmm, below you do something like that:

     if (!has_polarity) {
         polarity = POLARITY_VERTICAL_MEDIUM;
     }

... so it rather seems like medium polarity is the default? ... that looks 
weird. I think you should maybe rather pass the has_polarity and 
has_dedication flags to the s390_change_topology() function and only change 
the value if they have really been provided?

> +# @dedicated: optional, if the vCPU is dedicated to a real CPU
> +#
> +# Modifies the topology by moving the CPU inside the topology
> +# tree or by changing a modifier attribute of a CPU.
> +#
> +# Returns: Nothing on success, the reason on failure.
> +#
> +# Since: <next qemu stable release, eg. 1.0>

Please replace with "Since: 8.0" ... I hope we'll get it merged during this 
cycle!

> +{ 'command': 'x-set-cpu-topology',
> +  'data': {
> +      'core': 'int',
> +      'socket': 'int',
> +      'book': 'int',
> +      'drawer': 'int',
> +      '*polarity': 'int',
> +      '*dedicated': 'bool'
> +  },
> +  'if': { 'all': [ 'TARGET_S390X', 'CONFIG_KVM' ] }
> +}
> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
> index 1b3bdcb446..12827479cf 100644
> --- a/include/monitor/hmp.h
> +++ b/include/monitor/hmp.h
> @@ -151,5 +151,6 @@ void hmp_human_readable_text_helper(Monitor *mon,
>                                       HumanReadableText *(*qmp_handler)(Error **));
>   void hmp_info_stats(Monitor *mon, const QDict *qdict);
>   void hmp_pcie_aer_inject_error(Monitor *mon, const QDict *qdict);
> +void hmp_x_set_cpu_topology(Monitor *mon, const QDict *qdict);
>   
>   #endif
> diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
> index c33378577b..6c50050991 100644
> --- a/hw/s390x/cpu-topology.c
> +++ b/hw/s390x/cpu-topology.c
> @@ -18,6 +18,10 @@
>   #include "target/s390x/cpu.h"
>   #include "hw/s390x/s390-virtio-ccw.h"
>   #include "hw/s390x/cpu-topology.h"
> +#include "qapi/qapi-commands-machine-target.h"
> +#include "qapi/qmp/qdict.h"
> +#include "monitor/hmp.h"
> +#include "monitor/monitor.h"
>   
>   /*
>    * s390_topology is used to keep the topology information.
> @@ -379,3 +383,87 @@ void s390_topology_set_cpu(MachineState *ms, S390CPU *cpu, Error **errp)
>       /* topology tree is reflected in props */
>       s390_update_cpu_props(ms, cpu);
>   }
> +
> +/*
> + * qmp and hmp implementations
> + */
> +
> +static void s390_change_topology(int64_t core_id, int64_t socket_id,
> +                                 int64_t book_id, int64_t drawer_id,
> +                                 int64_t polarity, bool dedicated,
> +                                 Error **errp)
> +{
> +    MachineState *ms = current_machine;
> +    S390CPU *cpu;
> +    ERRP_GUARD();
> +
> +    cpu = (S390CPU *)ms->possible_cpus->cpus[core_id].cpu;

I think you should add a sanity check for core_id being in a valid range ... 
otherwise this will cause an access beyond the end of the array if core_id 
is too big or negative.

> +    if (!cpu) {
> +        error_setg(errp, "Core-id %ld does not exist!", core_id);
> +        return;
> +    }
> +
> +    /* Verify the new topology */
> +    s390_topology_check(cpu, errp);
> +    if (*errp) {
> +        return;
> +    }
> +
> +    /* Move the CPU into its new socket */
> +    s390_set_core_in_socket(cpu, drawer_id, book_id, socket_id, true, errp);
> +
> +    /* All checks done, report topology in environment */
> +    cpu->env.drawer_id = drawer_id;
> +    cpu->env.book_id = book_id;
> +    cpu->env.socket_id = socket_id;
> +    cpu->env.dedicated = dedicated;
> +    cpu->env.entitlement = polarity;

As mentioned above, I think dedicated and polarity should only be changed if 
they have really been provided?

> +    /* topology tree is reflected in props */
> +    s390_update_cpu_props(ms, cpu);
> +
> +    /* Advertise the topology change */
> +    s390_cpu_topology_set_modified();
> +}
> +
> +void qmp_x_set_cpu_topology(int64_t core, int64_t socket,
> +                         int64_t book, int64_t drawer,
> +                         bool has_polarity, int64_t polarity,
> +                         bool has_dedicated, bool dedicated,
> +                         Error **errp)
> +{
> +    ERRP_GUARD();
> +
> +    if (!s390_has_topology()) {
> +        error_setg(errp, "This machine doesn't support topology");
> +        return;
> +    }
> +    if (!has_polarity) {
> +        polarity = POLARITY_VERTICAL_MEDIUM;
> +    }
> +    if (!has_dedicated) {
> +        dedicated = false;
> +    }
> +    s390_change_topology(core, socket, book, drawer, polarity, dedicated, errp);
> +}
> +
> +void hmp_x_set_cpu_topology(Monitor *mon, const QDict *qdict)
> +{
> +    const int64_t core = qdict_get_int(qdict, "core");
> +    const int64_t socket = qdict_get_int(qdict, "socket");
> +    const int64_t book = qdict_get_int(qdict, "book");
> +    const int64_t drawer = qdict_get_int(qdict, "drawer");
> +    bool has_polarity    = qdict_haskey(qdict, "polarity");
> +    const int64_t polarity = qdict_get_try_int(qdict, "polarity", 0);
> +    bool has_dedicated    = qdict_haskey(qdict, "dedicated");
> +    const bool dedicated = qdict_get_try_bool(qdict, "dedicated", false);
> +    Error *local_err = NULL;
> +
> +    qmp_x_set_cpu_topology(core, socket, book, drawer,
> +                           has_polarity, polarity,
> +                           has_dedicated, dedicated,
> +                           &local_err);
> +    if (hmp_handle_error(mon, local_err)) {
> +        return;
> +    }
> +}
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index 673e39a697..bb3c908356 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -1815,3 +1815,19 @@ SRST
>     Dump the FDT in dtb format to *filename*.
>   ERST
>   #endif
> +
> +#if defined(TARGET_S390X) && defined(CONFIG_KVM)
> +    {
> +        .name       = "x-set-cpu-topology",
> +        .args_type  = "core:l,socket:l,book:l,drawer:l,polarity:l?,dedicated:b?",
> +        .params     = "core socket book drawer [polarity] [dedicated]",
> +        .help       = "Move CPU 'core' to 'socket/book/drawer' "
> +                      "optionaly modifies polarity and dedication",

optionaly ==> optionally

> +        .cmd        = hmp_x_set_cpu_topology,
> +    },
> +
> +SRST
> +``x-set-cpu-topology`` *core* *socket* *book* *drawer* *polarity* *dedicated*
> +  Moves the CPU  *core* to *socket* *book* *drawer* with *polarity* *dedicated*.
> +ERST
> +#endif

  Thomas