Re: [PATCH 2/2] hw/acpi: i386: bump MADT to revision 5

[Eric DeVolder]

On 4/12/23 02:58, Igor Mammedov wrote:
> On Tue, 11 Apr 2023 18:00:49 +0200
> Igor Mammedov <imammedo@redhat.com> wrote:
>
> > On Tue, 28 Mar 2023 11:59:26 -0400
> > 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).
> >
> > So spec mandates 3 possible states
> >    00t - not present and not can't be added later ever
> >    01t - present
> >    10t - not present but might be added later
> > and outlawed 11t combination
> >
> > 00t - doesn't make much sense (i.e. why put such entry in MADT in the 1st place)
> >
> > but looking at kernel commit aa06e20f1be, it looks like
> > ACPI_MADT_ONLINE_CAPABLE was introduced to accommodate
> > firmware/hw folks who would stuff MADT with LAPIC entries
> > for all possible CPU models, and then patch it depending on
> > actually used CPU model instead of dynamically creating LAPIC
> > entries. (insane)
>
> on second thought, QEMU doesn't need rev 5 MADT with this flag complications.
> Also I see that kernel side fix ended up in checking ACPI spec version instead
> of dealing with MADT revisions mess.
>
> So for x86 lets bump revision to 3 or 4 to be in sync with
> what QEMU actually uses.

If bumping to only 3 or 4, then there is no need for this patch series.

>    
> >   
> > > 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..1e3a13a36c 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 /* Enabled */ : false;
> > > +    /*
> > > +     * ACPI 6.3 5.2.12.2 Local APIC Flags: OnlineCapable must be 0
> > > +     * if Enabled is set.
> > > +     */
> > > +    bool onlinecapable = enabled ? false : true; /* Online Capable */
> >
> > > +    uint32_t flags = onlinecapable ? 0x2 : 0x0 |
> > > +        enabled ? 0x1 : 0x0;
> > align the last line with onlinecapable ....'
> >
> > move /* Enabled */ and /* Online Capable */ comments right to magic values
> > i.e. onlinecapable ? 0x2 : 0x0 | /* Online Capable */ ...

Done.

I've gone ahead and posted a v2 with these changes; keeping MADT.revision at 5.
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);