[libvirt] [PATCHv2 11/11] qemu_driver: BaselineHypervisorCPU supports S390 using QEMU/QMP

[Jiri Denemark]

On Mon, Jul 09, 2018 at 22:56:55 -0500, Chris Venteicher wrote:
> Transient S390 configurations require using QEMU to compute CPU Model
> Baseline and to do CPU Feature Expansion.
> 
> Start and use a single QEMU instance to do both the baseline and
> expansion transactions required by BaselineHypervisorCPU.
> 
> CPU Feature Expansion uses true / false to indicate if property is/isn't
> included in model. Baseline only returns property list where all
> enumerated properties are included.

So are you saying on s390 there's no chance there would be a CPU model
with some feature which is included in the CPU model disabled for some
reason? Sounds too good to be true :-) (This is the question I referred
to in one of my replies to the other patches.)

Most of the code you added in this patch is indented by three spaces
while we use four spaces in libvirt.

> ---
>  src/qemu/qemu_driver.c | 74 +++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 65 insertions(+), 9 deletions(-)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 9a35e04a85..6c6107f077 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -13400,10 +13400,13 @@ qemuConnectBaselineHypervisorCPU(virConnectPtr conn,
>      virArch arch;
>      virDomainVirtType virttype;
>      virDomainCapsCPUModelsPtr cpuModels;
> -    bool migratable;
> +    bool migratable_only;

Why? The bool says the user specified
VIR_CONNECT_BASELINE_CPU_MIGRATABLE which means they want a migratable
CPU back. What does the "_only" part mean? This API does not return
several CPUs, it only returns a single one and it's either migratable or
not.

>      virCPUDefPtr cpu = NULL;
>      char *cpustr = NULL;
>      char **features = NULL;
> +    virQEMUCapsInitQMPCommandPtr cmd = NULL;
> +    bool forceTCG = false;
> +    qemuMonitorCPUModelInfoPtr modelInfo = NULL;
>  
>      virCheckFlags(VIR_CONNECT_BASELINE_CPU_EXPAND_FEATURES |
>                    VIR_CONNECT_BASELINE_CPU_MIGRATABLE, NULL);
> @@ -13411,8 +13414,6 @@ qemuConnectBaselineHypervisorCPU(virConnectPtr conn,
>      if (virConnectBaselineHypervisorCPUEnsureACL(conn) < 0)
>          goto cleanup;
>  
> -    migratable = !!(flags & VIR_CONNECT_BASELINE_CPU_MIGRATABLE);
> -
>      if (!(cpus = virCPUDefListParse(xmlCPUs, ncpus, VIR_CPU_TYPE_AUTO)))
>          goto cleanup;
>  
> @@ -13425,6 +13426,19 @@ qemuConnectBaselineHypervisorCPU(virConnectPtr conn,
>      if (!qemuCaps)
>          goto cleanup;
>  
> +    /* QEMU can enumerate non-migratable cpu model features for some archs like x86
> +     * migratable_only == true:  ask for and include only migratable features
> +     * migratable_only == false: ask for and include all features
> +     */
> +    migratable_only = !!(flags & VIR_CONNECT_BASELINE_CPU_MIGRATABLE);
> +
> +    if (ARCH_IS_S390(arch)) {
> +       /* QEMU for S390 arch only enumerates migratable features
> +        * No reason to explicitly ask QEMU for or include non-migratable features
> +        */
> +       migratable_only = true;
> +    }
> +

And what if they come up with some features which are not migratable in
the future? I don't think there's any reason for this API to mess with
the value. The code should just provide the same CPU in both cases for
s390.

>      if (!(cpuModels = virQEMUCapsGetCPUDefinitions(qemuCaps, virttype)) ||
>          cpuModels->nmodels == 0) {
>          virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
> @@ -13437,18 +13451,31 @@ qemuConnectBaselineHypervisorCPU(virConnectPtr conn,
>  
>      if (ARCH_IS_X86(arch)) {
>          int rc = virQEMUCapsGetCPUFeatures(qemuCaps, virttype,
> -                                           migratable, &features);
> +                                           migratable_only, &features);
>          if (rc < 0)
>              goto cleanup;
>          if (features && rc == 0) {
>              /* We got only migratable features from QEMU if we asked for them,
>               * no further filtering in virCPUBaseline is desired. */
> -            migratable = false;
> +            migratable_only = false;
>          }
>  
>          if (!(cpu = virCPUBaseline(arch, cpus, ncpus, cpuModels,
> -                                   (const char **)features, migratable)))
> +                                   (const char **)features, migratable_only)))
>              goto cleanup;
> +    } else if (ARCH_IS_S390(arch)) {
> +

No need for this extra empty line.

> +       const char *binary = virQEMUCapsGetBinary(qemuCaps);
> +       virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
> +
> +       if (!(cmd = virQEMUCapsNewQMPCommandConnection(binary, cfg->libDir,
> +                                                      cfg->user, cfg->group,
> +                                                      forceTCG)))
> +          goto cleanup;
> +
> +       if ((virQEMUCapsQMPBaselineCPUModel(cmd, cpus, &cpu) < 0) || !cpu)

Hmm, I think you should only call this when the user passed more than
one CPU. This API is expected to work even with a single CPU in which
case it just expands it if the corresponding flag was set.

> +          goto cleanup; /* Content Error */

What did you want to say with the comment? I think you can safely drop
it.

> +

And this one either.

>      } else {
>          virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
>                         _("computing baseline hypervisor CPU is not supported "
> @@ -13458,9 +13485,36 @@ qemuConnectBaselineHypervisorCPU(virConnectPtr conn,
>  
>      cpu->fallback = VIR_CPU_FALLBACK_FORBID;
>  
> -    if ((flags & VIR_CONNECT_BASELINE_CPU_EXPAND_FEATURES) &&
> -        virCPUExpandFeatures(arch, cpu) < 0)
> -        goto cleanup;
> +    if (flags & VIR_CONNECT_BASELINE_CPU_EXPAND_FEATURES) {
> +       if (ARCH_IS_X86(arch)) {
> +          if (virCPUExpandFeatures(arch, cpu) < 0)
> +             goto cleanup;
> +       } else if (ARCH_IS_S390(arch)) {
> +

Extra empty line.

> +          if (!(modelInfo = virQEMUCapsCPUModelInfoFromCPUDef(cpu)))
> +             goto cleanup;
> +
> +          virCPUDefFree(cpu); /* Null on failure, repopulated on success */

I think it would be better to drop the comment and just do it:

             cpu = NULL;

Oh and since this goes from CPUDef to modelInfo and back, you may
actually need to do some extra work to persist some parts of the
original CPU definitions which get lost during the translation (e.g.,
the CPU vendor) if it's applicable for s390. We have to do similar stuff
for x86 too when we translate CPUDef into CPUID bits and back.

> +
> +          if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_QUERY_CPU_MODEL_EXPANSION)) {
> +             virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> +                            _("Feature Expansion not supported with this QEMU binary"));
> +             goto cleanup;
> +          }

Is this necessary? Can't qemuMonitorGetCPUModelExpansion just report the
error when it tries to call an unsupported QMP command? Or is the error
message confusing?

> +
> +          if (qemuMonitorGetCPUModelExpansion(cmd->mon,
> +                                              QEMU_MONITOR_CPU_MODEL_EXPANSION_FULL,
> +                                              migratable_only, modelInfo) < 0)
> +             goto cleanup;
> +
> +          /* Expansion enumerates all features
> +           * Baseline reply enumerates only in-model (true) features */
> +          qemuMonitorCPUModelInfoRemovePropByBoolValue(modelInfo, false);
> +
> +          if (!(cpu = virQEMUCapsCPUModelInfoToCPUDef(migratable_only, modelInfo)))
> +             goto cleanup;
> +       }
> +    }
>  
>      cpustr = virCPUDefFormat(cpu, NULL);
>  
> @@ -13469,6 +13523,8 @@ qemuConnectBaselineHypervisorCPU(virConnectPtr conn,
>      virCPUDefFree(cpu);
>      virObjectUnref(qemuCaps);
>      virStringListFree(features);
> +    virQEMUCapsInitQMPCommandFree(cmd);
> +    qemuMonitorCPUModelInfoFree(modelInfo);
>  
>      return cpustr;
>  }

Jirka