Re: [Qemu-devel] [PATCH v3 05/13] pc: leave max apic_id_limit only in legacy cpu hotplug code

[Igor Mammedov]

On Mon, 17 Oct 2016 19:44:52 -0200
Eduardo Habkost <address@hidden> wrote:

> On Thu, Oct 13, 2016 at 11:52:39AM +0200, Igor Mammedov wrote:
> [...]
> > @@ -236,7 +237,11 @@ void build_legacy_cpu_hotplug_aml(Aml *ctx, 
> > MachineState *machine,
> >      /* The current AML generator can cover the APIC ID range [0..255],
> >       * inclusive, for VCPU hotplug. */
> >      QEMU_BUILD_BUG_ON(ACPI_CPU_HOTPLUG_ID_LIMIT > 256);
> > -    g_assert(pcms->apic_id_limit <= ACPI_CPU_HOTPLUG_ID_LIMIT);
> > +    if (pcms->apic_id_limit > ACPI_CPU_HOTPLUG_ID_LIMIT) {
> > +        error_report("max_cpus is too large. APIC ID of last CPU is %u",
> > +                     pcms->apic_id_limit - 1);
> > +        exit(1);
> > +    }  
> 
> Moving the check here seems to make sense, but:
> 
> >  
> >      /* create PCI0.PRES device and its _CRS to reserve CPU hotplug MMIO */
> >      dev = aml_device("PCI0." stringify(CPU_HOTPLUG_RESOURCE_DEVICE));
> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > index 93ff49c..f1c1013 100644
> > --- a/hw/i386/pc.c
> > +++ b/hw/i386/pc.c
> > @@ -778,7 +778,6 @@ static FWCfgState *bochs_bios_init(AddressSpace *as, 
> > PCMachineState *pcms)  
> 
> [Added more context below to show the code around the change]
> 
> >      numa_fw_cfg = g_new0(uint64_t, 1 + pcms->apic_id_limit + 
> > nb_numa_nodes);
> >      numa_fw_cfg[0] = cpu_to_le64(nb_numa_nodes);
> >      for (i = 0; i < max_cpus; i++) {
> >          unsigned int apic_id = x86_cpu_apic_id_from_index(i);
> > -        assert(apic_id < pcms->apic_id_limit);  
> 
> If you really needed to remove this assert, that means you can
> write beyond the end of numa_fw_fg[] below. Are you sure you need
> to remove it?
> 
> >          j = numa_get_node_for_cpu(i);
> >          if (j < nb_numa_nodes) {
> >              numa_fw_cfg[apic_id + 1] = cpu_to_le64(j);  
> 
>                            ^^^^^^^^^^^ here
Shouldn't above
  numa_fw_cfg = g_new0(uint64_t, 1 + pcms->apic_id_limit + nb_numa_nodes);
allocate sufficiently sized array?

That's aside, the assert could be kept as it doesn't get in a way
if you'd prefer it that way.

> >          }
> >      }
> > 
> > @@ -1190,12 +1189,6 @@ void pc_cpus_init(PCMachineState *pcms)
> >       * This is used for FW_CFG_MAX_CPUS. See comments on bochs_bios_init().
> >       */
> >      pcms->apic_id_limit = x86_cpu_apic_id_from_index(max_cpus - 1) + 1;
> > -    if (pcms->apic_id_limit > ACPI_CPU_HOTPLUG_ID_LIMIT) {
> > -        error_report("max_cpus is too large. APIC ID of last CPU is %u",
> > -                     pcms->apic_id_limit - 1);
> > -        exit(1);
> > -    }
> > -
> >      pcms->possible_cpus = g_malloc0(sizeof(CPUArchIdList) +
> >                                      sizeof(CPUArchId) * max_cpus);
> >      for (i = 0; i < max_cpus; i++) {
> > -- 
> > 2.7.4
> >   
>