[libvirt PATCH v2 1/1] qemuProcessUpdateGuestCPU: Check host cpu for forbidden features

[Jiri Denemark]

On Thu, Feb 25, 2021 at 14:23:06 +0100, Tim Wiederhake wrote:
> See https://bugzilla.redhat.com/show_bug.cgi?id=1840770
> 
> Signed-off-by: Tim Wiederhake <twiederh at redhat.com>
> ---
>  src/qemu/qemu_process.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index bfa742577f..cecf606312 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -6149,6 +6149,33 @@ qemuProcessUpdateGuestCPU(virDomainDefPtr def,
>      if (virCPUConvertLegacy(hostarch, def->cpu) < 0)
>          return -1;
>  
> +    if (def->cpu->check != VIR_CPU_CHECK_NONE) {
> +        virCPUDefPtr host;
> +        size_t i;
> +
> +        host = virQEMUCapsGetHostModel(qemuCaps, def->virtType,
> +                                       VIR_QEMU_CAPS_HOST_CPU_FULL);
> +
> +        for (i = 0; i < def->cpu->nfeatures; ++i) {
> +            virCPUFeatureDefPtr feature;
> +
> +            if (def->cpu->features[i].policy != VIR_CPU_FEATURE_FORBID)
> +                continue;
> +
> +            feature = virCPUDefFindFeature(host, def->cpu->features[i].name);

This would crash in case virQEMUCapsGetHostModel returned NULL, which
may happen quite easily, especially on non-x86 architectures.

> +            if (!feature)
> +                continue;
> +
> +            if (feature->policy == VIR_CPU_FEATURE_DISABLE)
> +                continue;
> +
> +            virReportError(VIR_ERR_CPU_INCOMPATIBLE,
> +                           _("Host CPU provides forbidden feature '%s'"),
> +                           def->cpu->features[i].name);
> +            return -1;
> +        }
> +    }
> +

This new code is a good candidate for separation into a new function. I
believe we don't need architecture specific implementation for this
function, but something like virCPUCheckForbiddenFeatures in
src/cpu/cpu.c seems like a logical choice.

>      /* nothing to update for host-passthrough / maximum */
>      if (def->cpu->mode != VIR_CPU_MODE_HOST_PASSTHROUGH &&
>          def->cpu->mode != VIR_CPU_MODE_MAXIMUM) {

Jirka