Re: [PATCH v5 1/3] hw/i386/pc: Refactor logic to set SMBIOS defaults

[Daniel P . Berrangé]

On Tue, Jun 06, 2023 at 09:49:37PM -0500, Suravee Suthikulpanit wrote:
> Into a helper function pc_machine_init_smbios() in preparation for
> subsequent code to upgrade default SMBIOS entry point type.
> 
> Then, call the helper function from the pc_machine_initfn() to eliminate
> duplicate code in pc_q35.c and pc_pixx.c. However, this changes the
> ordering of when the smbios_set_defaults() is called to before
> pc_machine_set_smbios_ep() (i.e. before handling the user specified
> QEMU option "-M ...,smbios-entry-point-type=[32|64]" to override
> the default type.)
> 
> Therefore, also call the helper function in pc_machine_set_smbios_ep()
> to update the defaults.

This is unsafe - smbios_set_defaults is only intended to be called
once. Calling it twice leads to a SEGV due to double-free

$  ./build/qemu-system-x86_64 -machine pc,smbios-entry-point-type=64 -smbios 
file=/tmp/smbios_entry_point
Segmentation fault (core dumped)

IMHO we should just not do this refactoring. The existing duplicated
code is not a significant burden, and thus is better than having to
workaround calling pc_machine_set_smbios_ep too early in startup.

> 
> There is no functional change.
> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
>  hw/i386/pc.c      | 24 +++++++++++++++++++++++-
>  hw/i386/pc_piix.c |  9 ---------
>  hw/i386/pc_q35.c  |  8 --------
>  3 files changed, 23 insertions(+), 18 deletions(-)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index bb62c994fa..b720dc67b6 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1756,6 +1756,22 @@ static void 
> pc_machine_set_default_bus_bypass_iommu(Object *obj, bool value,
>      pcms->default_bus_bypass_iommu = value;
>  }
>  
> +static void pc_machine_init_smbios(PCMachineState *pcms)
> +{
> +    PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
> +    MachineClass *mc = MACHINE_GET_CLASS(pcms);
> +
> +    if (!pcmc->smbios_defaults) {
> +        return;
> +    }
> +
> +    /* These values are guest ABI, do not change */
> +    smbios_set_defaults("QEMU", mc->desc,
> +                        mc->name, pcmc->smbios_legacy_mode,
> +                        pcmc->smbios_uuid_encoded,
> +                        pcms->smbios_entry_point_type);
> +}
> +
>  static void pc_machine_get_smbios_ep(Object *obj, Visitor *v, const char 
> *name,
>                                       void *opaque, Error **errp)
>  {
> @@ -1768,9 +1784,14 @@ static void pc_machine_get_smbios_ep(Object *obj, 
> Visitor *v, const char *name,
>  static void pc_machine_set_smbios_ep(Object *obj, Visitor *v, const char 
> *name,
>                                       void *opaque, Error **errp)
>  {
> +    SmbiosEntryPointType ep_type;
>      PCMachineState *pcms = PC_MACHINE(obj);
>  
> -    visit_type_SmbiosEntryPointType(v, name, &pcms->smbios_entry_point_type, 
> errp);
> +    if (!visit_type_SmbiosEntryPointType(v, name, &ep_type, errp)) {
> +        return;
> +    }
> +    pcms->smbios_entry_point_type = ep_type;
> +    pc_machine_init_smbios(pcms);
>  }
>  
>  static void pc_machine_get_max_ram_below_4g(Object *obj, Visitor *v,
> @@ -1878,6 +1899,7 @@ static void pc_machine_initfn(Object *obj)
>      object_property_add_alias(OBJECT(pcms), "pcspk-audiodev",
>                                OBJECT(pcms->pcspk), "audiodev");
>      cxl_machine_init(obj, &pcms->cxl_devices_state);
> +    pc_machine_init_smbios(pcms);
>  }
>  
>  int pc_machine_kvm_type(MachineState *machine, const char *kvm_type)
> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> index d5b0dcd1fe..da6ba4eeb4 100644
> --- a/hw/i386/pc_piix.c
> +++ b/hw/i386/pc_piix.c
> @@ -198,15 +198,6 @@ static void pc_init1(MachineState *machine,
>  
>      pc_guest_info_init(pcms);
>  
> -    if (pcmc->smbios_defaults) {
> -        MachineClass *mc = MACHINE_GET_CLASS(machine);
> -        /* These values are guest ABI, do not change */
> -        smbios_set_defaults("QEMU", mc->desc,
> -                            mc->name, pcmc->smbios_legacy_mode,
> -                            pcmc->smbios_uuid_encoded,
> -                            pcms->smbios_entry_point_type);
> -    }
> -
>      /* allocate ram and load rom/bios */
>      if (!xen_enabled()) {
>          pc_memory_init(pcms, system_memory, rom_memory, hole64_size);
> diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> index 6155427e48..a58cd1d3ea 100644
> --- a/hw/i386/pc_q35.c
> +++ b/hw/i386/pc_q35.c
> @@ -198,14 +198,6 @@ static void pc_q35_init(MachineState *machine)
>  
>      pc_guest_info_init(pcms);
>  
> -    if (pcmc->smbios_defaults) {
> -        /* These values are guest ABI, do not change */
> -        smbios_set_defaults("QEMU", mc->desc,
> -                            mc->name, pcmc->smbios_legacy_mode,
> -                            pcmc->smbios_uuid_encoded,
> -                            pcms->smbios_entry_point_type);
> -    }
> -
>      /* create pci host bus */
>      q35_host = Q35_HOST_DEVICE(qdev_new(TYPE_Q35_HOST_DEVICE));
>  
> -- 
> 2.34.1
> 

With regards,
Daniel
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