Re: [PATCH for-6.2 v2 01/11] machine: Disallow specifying topology parameters as zero

[Andrew Jones]

On Mon, Jul 19, 2021 at 11:20:33AM +0800, Yanan Wang wrote:
> In the SMP configuration, we should either specify a topology
> parameter with a reasonable value (equal to or greater than 1)
> or just leave it omitted and QEMU will calculate its value.
> 
> Configurations which explicitly specify the topology parameters
> as zero like "sockets=0" are meaningless, so disallow them.
> 
> Suggested-by: Andrew Jones <drjones@redhat.com>
> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> ---
>  hw/core/machine.c | 31 +++++++++++++++++++++++--------
>  hw/i386/pc.c      | 29 +++++++++++++++++++++--------
>  qapi/machine.json |  4 ++--
>  3 files changed, 46 insertions(+), 18 deletions(-)
> 
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 775add0795..d73daa10f4 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -745,11 +745,25 @@ static void smp_parse(MachineState *ms, 
> SMPConfiguration *config, Error **errp)
>  {
>      unsigned cpus    = config->has_cpus ? config->cpus : 0;
>      unsigned sockets = config->has_sockets ? config->sockets : 0;
> +    unsigned dies    = config->has_dies ? config->dies : 1;
>      unsigned cores   = config->has_cores ? config->cores : 0;
>      unsigned threads = config->has_threads ? config->threads : 0;
> +    unsigned maxcpus = config->has_maxcpus ? config->maxcpus : 0;
> +
> +    if ((config->has_cpus && config->cpus == 0) ||
> +        (config->has_sockets && config->sockets == 0) ||
> +        (config->has_dies && config->dies == 0) ||
> +        (config->has_cores && config->cores == 0) ||
> +        (config->has_threads && config->threads == 0) ||
> +        (config->has_maxcpus && config->maxcpus == 0)) {
> +        error_setg(errp, "parameters must be equal to or greater than one"
> +                   "if provided");

Missing a space between 'one' and 'if'. It's better to just put the whole
string on one line too (ignore the 80 char thing) for error grepping.

> +        return;
> +    }
>  
> -    if (config->has_dies && config->dies != 0 && config->dies != 1) {
> +    if (dies > 1) {
>          error_setg(errp, "dies not supported by this machine's CPU 
> topology");
> +        return;
>      }
>  
>      /* compute missing values, prefer sockets over cores over threads */
> @@ -760,8 +774,8 @@ static void smp_parse(MachineState *ms, SMPConfiguration 
> *config, Error **errp)
>              sockets = sockets > 0 ? sockets : 1;
>              cpus = cores * threads * sockets;
>          } else {
> -            ms->smp.max_cpus = config->has_maxcpus ? config->maxcpus : cpus;
> -            sockets = ms->smp.max_cpus / (cores * threads);
> +            maxcpus = maxcpus > 0 ? maxcpus : cpus;
> +            sockets = maxcpus / (cores * threads);
>          }
>      } else if (cores == 0) {
>          threads = threads > 0 ? threads : 1;
> @@ -778,26 +792,27 @@ static void smp_parse(MachineState *ms, 
> SMPConfiguration *config, Error **errp)
>          return;
>      }
>  
> -    ms->smp.max_cpus = config->has_maxcpus ? config->maxcpus : cpus;
> +    maxcpus = maxcpus > 0 ? maxcpus : cpus;
>  
> -    if (ms->smp.max_cpus < cpus) {
> +    if (maxcpus < cpus) {
>          error_setg(errp, "maxcpus must be equal to or greater than smp");
>          return;
>      }
>  
> -    if (sockets * cores * threads != ms->smp.max_cpus) {
> +    if (sockets * cores * threads != maxcpus) {
>          error_setg(errp, "Invalid CPU topology: "
>                     "sockets (%u) * cores (%u) * threads (%u) "
>                     "!= maxcpus (%u)",
>                     sockets, cores, threads,
> -                   ms->smp.max_cpus);
> +                   maxcpus);
>          return;
>      }
>  
>      ms->smp.cpus = cpus;
> +    ms->smp.sockets = sockets;
>      ms->smp.cores = cores;
>      ms->smp.threads = threads;
> -    ms->smp.sockets = sockets;
> +    ms->smp.max_cpus = maxcpus;
>  }
>  
>  static void machine_get_smp(Object *obj, Visitor *v, const char *name,
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index c2b9d62a35..c6b63c00a5 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -719,6 +719,18 @@ static void pc_smp_parse(MachineState *ms, 
> SMPConfiguration *config, Error **err
>      unsigned dies    = config->has_dies ? config->dies : 1;
>      unsigned cores   = config->has_cores ? config->cores : 0;
>      unsigned threads = config->has_threads ? config->threads : 0;
> +    unsigned maxcpus = config->has_maxcpus ? config->maxcpus : 0;
> +
> +    if ((config->has_cpus && config->cpus == 0) ||
> +        (config->has_sockets && config->sockets == 0) ||
> +        (config->has_dies && config->dies == 0) ||
> +        (config->has_cores && config->cores == 0) ||
> +        (config->has_threads && config->threads == 0) ||
> +        (config->has_maxcpus && config->maxcpus == 0)) {
> +        error_setg(errp, "parameters must be equal to or greater than one"
> +                   "if provided");

Same comment as above.

> +        return;
> +    }
>  
>      /* compute missing values, prefer sockets over cores over threads */
>      if (cpus == 0 || sockets == 0) {
> @@ -728,8 +740,8 @@ static void pc_smp_parse(MachineState *ms, 
> SMPConfiguration *config, Error **err
>              sockets = sockets > 0 ? sockets : 1;
>              cpus = cores * threads * dies * sockets;
>          } else {
> -            ms->smp.max_cpus = config->has_maxcpus ? config->maxcpus : cpus;
> -            sockets = ms->smp.max_cpus / (cores * threads * dies);
> +            maxcpus = maxcpus > 0 ? maxcpus : cpus;
> +            sockets = maxcpus / (cores * threads * dies);
>          }
>      } else if (cores == 0) {
>          threads = threads > 0 ? threads : 1;
> @@ -746,27 +758,28 @@ static void pc_smp_parse(MachineState *ms, 
> SMPConfiguration *config, Error **err
>          return;
>      }
>  
> -    ms->smp.max_cpus = config->has_maxcpus ? config->maxcpus : cpus;
> +    maxcpus = maxcpus > 0 ? maxcpus : cpus;
>  
> -    if (ms->smp.max_cpus < cpus) {
> +    if (maxcpus < cpus) {
>          error_setg(errp, "maxcpus must be equal to or greater than smp");
>          return;
>      }
>  
> -    if (sockets * dies * cores * threads != ms->smp.max_cpus) {
> +    if (sockets * dies * cores * threads != maxcpus) {
>          error_setg(errp, "Invalid CPU topology deprecated: "
>                     "sockets (%u) * dies (%u) * cores (%u) * threads (%u) "
>                     "!= maxcpus (%u)",
>                     sockets, dies, cores, threads,
> -                   ms->smp.max_cpus);
> +                   maxcpus);
>          return;
>      }
>  
>      ms->smp.cpus = cpus;
> -    ms->smp.cores = cores;
> -    ms->smp.threads = threads;
>      ms->smp.sockets = sockets;
>      ms->smp.dies = dies;
> +    ms->smp.cores = cores;
> +    ms->smp.threads = threads;
> +    ms->smp.max_cpus = maxcpus;
>  }
>  
>  static
> diff --git a/qapi/machine.json b/qapi/machine.json
> index c3210ee1fb..c11b2e6f73 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1288,8 +1288,8 @@
>  ##
>  # @SMPConfiguration:
>  #
> -# Schema for CPU topology configuration.  "0" or a missing value lets
> -# QEMU figure out a suitable value based on the ones that are provided.
> +# Schema for CPU topology configuration. A missing value lets QEMU
> +# figure out a suitable value based on the ones that are provided.
>  #
>  # @cpus: number of virtual CPUs in the virtual machine
>  #
> -- 
> 2.19.1
> 

Otherwise

Reviewed-by: Andrew Jones <drjones@redhat.com>