Re: [PATCH v2 3/4] hw/acpi: i386: bump MADT to revision 5

[Eric DeVolder]

On 4/20/23 03:05, Ani Sinha wrote:
> On Tue, Apr 18, 2023 at 10:22 PM Eric DeVolder <eric.devolder@oracle.com> wrote:
> > Currently i386 QEMU generates MADT revision 3, and reports
> > MADT revision 1. ACPI 6.3 introduces MADT revision 5.
> >
> > For MADT revision 4, that introduces ARM GIC structures, which do
> > not apply to i386.
> >
> > For MADT revision 5, the Local APIC flags introduces the Online
> > Capable bitfield.
> >
> > Making MADT generate and report revision 5 will solve problems with
> > CPU hotplug (the Online Capable flag indicates hotpluggable CPUs).
> >
> > Link: 
> > https://lore.kernel.org/linux-acpi/20230327191026.3454-1-eric.devolder@oracle.com/T/#t
> > Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> > ---
> >   hw/i386/acpi-common.c | 13 ++++++++++---
> >   1 file changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/i386/acpi-common.c b/hw/i386/acpi-common.c
> > index 52e5c1439a..286c1c5c32 100644
> > --- a/hw/i386/acpi-common.c
> > +++ b/hw/i386/acpi-common.c
> > @@ -38,8 +38,15 @@ void pc_madt_cpu_entry(int uid, const CPUArchIdList 
> > *apic_ids,
> >   {
> >       uint32_t apic_id = apic_ids->cpus[uid].arch_id;
> >       /* Flags – Local APIC Flags */
> > -    uint32_t flags = apic_ids->cpus[uid].cpu != NULL || force_enabled ?
> > -                     1 /* Enabled */ : 0;
> > +    bool enabled = apic_ids->cpus[uid].cpu != NULL || force_enabled ?
> > +                     true : false;
>
> how about "processor_enabled" instead of just "enabled" as the variable name.
>
> > +    /*
> > +     * ACPI 6.3 5.2.12.2 Local APIC Flags: OnlineCapable must be 0
> > +     * if Enabled is set.
> > +     */
> > +    bool onlinecapable = enabled ? false : true;
>
> ugh, how about uint32 onlinecapable = enabled? 0x0 : 0x2 ?
>
> > +    uint32_t flags = onlinecapable ? 0x2 : 0x0 | /* Online Capable */
> > +                     enabled ? 0x1 : 0x0; /* Enabled */
>
> then here, flags = onlinecapable | processor_enabled? 0x1 : 0x0;

Colleague Miguel Luis pointed out that this is simpler and equivalent:

uint32_t flags = apic_ids->cpus[uid].cpu != NULL || force_enabled ? 1 /* Enabled */ : 2 /* Online 
Capable */;

Is that acceptable?
eric

> >       /* ACPI spec says that LAPIC entry for non present
> >        * CPU may be omitted from MADT or it must be marked
> > @@ -102,7 +109,7 @@ void acpi_build_madt(GArray *table_data, BIOSLinker *linker,
> >       MachineClass *mc = MACHINE_GET_CLASS(x86ms);
> >       const CPUArchIdList *apic_ids = mc->possible_cpu_arch_ids(MACHINE(x86ms));
> >       AcpiDeviceIfClass *adevc = ACPI_DEVICE_IF_GET_CLASS(adev);
> > -    AcpiTable table = { .sig = "APIC", .rev = 1, .oem_id = oem_id,
> > +    AcpiTable table = { .sig = "APIC", .rev = 5, .oem_id = oem_id,
> >                           .oem_table_id = oem_table_id };
> >
> >       acpi_table_begin(&table, table_data);
> > --
> > 2.31.1