Re: [Qemu-devel] [for-2.1 PATCH v2 2/2] i386/acpi-build: support hotplug of VCPU with APIC ID 0xFF

[Eduardo Habkost]

On Tue, Mar 18, 2014 at 04:03:25PM +0200, Michael S. Tsirkin wrote:
> On Mon, Mar 17, 2014 at 05:05:17PM +0100, Laszlo Ersek wrote:
> > Building on the previous patch, raise the maximal count of processor
> > objects / NTFY branches / CPON elements from 255 to 256. This allows the
> > VCPU with APIC ID 0xFF to be hotplugged.
> > 
> > Signed-off-by: Laszlo Ersek <address@hidden>
> 
> 
> I note that we still have:
>     if (endvalue >= MAX_CPUMASK_BITS) {
>         endvalue = MAX_CPUMASK_BITS - 1;
>         fprintf(stderr,
>             "qemu: NUMA: A max of %d VCPUs are supported\n",
>              MAX_CPUMASK_BITS);
>     }
> and MAX_CPUMASK_BITS is 255.
> 
> Seems inconsistent?
> 

MAX_CPUMASK_BITS (now renamed to MAX_CPUS) limits CPU indexes and total
CPU count. This patch is about APIC IDs (which may be larger than
max_cpus if threads-per-core or cores-per-socket is not a power of 2).

(That doesn't mean we can't decide to increase MAX_CPUS later, too.)


> > ---
> >  hw/i386/acpi-build.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > index 2bbefb5..c9fe07f 100644
> > --- a/hw/i386/acpi-build.c
> > +++ b/hw/i386/acpi-build.c
> > @@ -999,11 +999,16 @@ build_ssdt(GArray *table_data, GArray *linker,
> >             AcpiCpuInfo *cpu, AcpiPmInfo *pm, AcpiMiscInfo *misc,
> >             PcPciInfo *pci, PcGuestInfo *guest_info)
> >  {
> > -    int acpi_cpus = MIN(0xff, guest_info->apic_id_limit);
> > +    unsigned acpi_cpus = guest_info->apic_id_limit;
> >      int ssdt_start = table_data->len;
> >      uint8_t *ssdt_ptr;
> >      int i;
> >  
> > +    /* 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(acpi_cpus <= ACPI_CPU_HOTPLUG_ID_LIMIT);
> > +
> >      /* Copy header and patch values in the S3_ / S4_ / S5_ packages */
> >      ssdt_ptr = acpi_data_push(table_data, sizeof(ssdp_misc_aml));
> >      memcpy(ssdt_ptr, ssdp_misc_aml, sizeof(ssdp_misc_aml));
> > -- 
> > 1.8.3.1

-- 
Eduardo