Re: [RFC] ich9:cpuhp: add support for cpu hot-unplug with SMI broadcast enabled

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 26 Nov 2020 02:24:27 -0800
Ankur Arora <ankur.a.arora@oracle.com> wrote:

> On 2020-11-24 4:25 a.m., Igor Mammedov wrote:
> > If firmware negotiates ICH9_LPC_SMI_F_CPU_HOT_UNPLUG_BIT feature,
> > OSPM on CPU eject will set bit #4 in CPU hotplug block for to be
> > ejected CPU to mark it for removal by firmware and trigger SMI
> > upcall to let firmware do actual eject.
> > 
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > ---
> > PS:
> >    - abuse 5.1 machine type for now to turn off unplug feature
> >      (it will be moved to 5.2 machine type once new merge window is open)
> > ---
> >   include/hw/acpi/cpu.h           |  2 ++
> >   docs/specs/acpi_cpu_hotplug.txt | 11 +++++++++--
> >   hw/acpi/cpu.c                   | 18 ++++++++++++++++--
> >   hw/i386/acpi-build.c            |  5 +++++
> >   hw/i386/pc.c                    |  1 +
> >   hw/isa/lpc_ich9.c               |  2 +-
> >   6 files changed, 34 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/hw/acpi/cpu.h b/include/hw/acpi/cpu.h
> > index 0eeedaa491..999caaf510 100644
> > --- a/include/hw/acpi/cpu.h
> > +++ b/include/hw/acpi/cpu.h
> > @@ -22,6 +22,7 @@ typedef struct AcpiCpuStatus {
> >       uint64_t arch_id;
> >       bool is_inserting;
> >       bool is_removing;
> > +    bool fw_remove;
> >       uint32_t ost_event;
> >       uint32_t ost_status;
> >   } AcpiCpuStatus;
> > @@ -50,6 +51,7 @@ void cpu_hotplug_hw_init(MemoryRegion *as, Object *owner,
> >   typedef struct CPUHotplugFeatures {
> >       bool acpi_1_compatible;
> >       bool has_legacy_cphp;
> > +    bool fw_unplugs_cpu;
> >       const char *smi_path;
> >   } CPUHotplugFeatures;
> >   
> > diff --git a/docs/specs/acpi_cpu_hotplug.txt b/docs/specs/acpi_cpu_hotplug.txt
> > index 9bb22d1270..f68ef6e06c 100644
> > --- a/docs/specs/acpi_cpu_hotplug.txt
> > +++ b/docs/specs/acpi_cpu_hotplug.txt
> > @@ -57,7 +57,11 @@ read access:
> >                 It's valid only when bit 0 is set.
> >              2: Device remove event, used to distinguish device for which
> >                 no device eject request to OSPM was issued.
> > -           3-7: reserved and should be ignored by OSPM
> > +           3: reserved and should be ignored by OSPM
> > +           4: if set to 1, OSPM requests firmware to perform device eject,
> > +              firmware shall clear this event by writing 1 into it before
> > +              performing device eject> +           5-7: reserved and should be ignored by OSPM
> >       [0x5-0x7] reserved
> >       [0x8] Command data: (DWORD access)
> >             contains 0 unless value last stored in 'Command field' is one of:
> > @@ -82,7 +86,10 @@ write access:
> >                  selected CPU device
> >               3: if set to 1 initiates device eject, set by OSPM when it
> >                  triggers CPU device removal and calls _EJ0 method
> > -            4-7: reserved, OSPM must clear them before writing to register
> > +            4: if set to 1 OSPM hands over device eject to firmware,
> > +               Firmware shall issue device eject request as described above
> > +               (bit #3) and OSPM should not touch device eject bit (#3),
> > +            5-7: reserved, OSPM must clear them before writing to register
> >       [0x5] Command field: (1 byte access)
> >             value:
> >               0: selects a CPU device with inserting/removing events and
> > diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c
> > index f099b50927..09d2f20dae 100644
> > --- a/hw/acpi/cpu.c
> > +++ b/hw/acpi/cpu.c
> > @@ -71,6 +71,7 @@ static uint64_t cpu_hotplug_rd(void *opaque, hwaddr addr, unsigned size)
> >           val |= cdev->cpu ? 1 : 0;
> >           val |= cdev->is_inserting ? 2 : 0;
> >           val |= cdev->is_removing  ? 4 : 0;
> > +        val |= cdev->fw_remove  ? 16 : 0;  
> 
> I might be missing something but I don't see where cdev->fw_remove is being
> set. We do set cdev->is_removing in acpi_cpu_unplug_request_cb() so AFAICS
> we would always end up setting this bit:
> >           val |= cdev->is_removing  ? 4 : 0;  
> 
> Also, if cdev->fw_remove and cdev->is_removing are both true, val would be
> (4 | 16). I'm guessing that in that case the AML determines which case gets
> handled but it might make sense to set just one of these?

cdev->fw_remove is set by AML when OSPM thinks it's ready to remove the CPU,
see "aml_append(method, aml_store(one, fw_ej_evt));" in this patch.

cdev->is_removing is set by QEMU's device_del command, and processed by AML
(which includes it being cleared before OSPM calls EJ0), it only serves
as flag for generating eject notification to OSPM.

> 
> 
> >           trace_cpuhp_acpi_read_flags(cpu_st->selector, val);
> >           break;
> >       case ACPI_CPU_CMD_DATA_OFFSET_RW:
> > @@ -148,6 +149,8 @@ static void cpu_hotplug_wr(void *opaque, hwaddr addr, uint64_t data,
> >               hotplug_ctrl = qdev_get_hotplug_handler(dev);
> >               hotplug_handler_unplug(hotplug_ctrl, dev, NULL);
> >               object_unparent(OBJECT(dev));
> > +        } else if (data & 16) {
> > +            cdev->fw_remove = !cdev->fw_remove;
> >           }
> >           break;
> >       case ACPI_CPU_CMD_OFFSET_WR:
> > @@ -332,6 +335,7 @@ const VMStateDescription vmstate_cpu_hotplug = {
> >   #define CPU_INSERT_EVENT  "CINS"
> >   #define CPU_REMOVE_EVENT  "CRMV"
> >   #define CPU_EJECT_EVENT   "CEJ0"
> > +#define CPU_FW_EJECT_EVENT "CEJF"
> >   
> >   void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
> >                       hwaddr io_base,
> > @@ -384,7 +388,10 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
> >           aml_append(field, aml_named_field(CPU_REMOVE_EVENT, 1));
> >           /* initiates device eject, write only */
> >           aml_append(field, aml_named_field(CPU_EJECT_EVENT, 1));
> > -        aml_append(field, aml_reserved_field(4));
> > +        aml_append(field, aml_reserved_field(1));
> > +        /* tell firmware to do device eject, write only */
> > +        aml_append(field, aml_named_field(CPU_FW_EJECT_EVENT, 1));
> > +        aml_append(field, aml_reserved_field(2));
> >           aml_append(field, aml_named_field(CPU_COMMAND, 8));
> >           aml_append(cpu_ctrl_dev, field);
> >   
> > @@ -419,6 +426,7 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
> >           Aml *ins_evt = aml_name("%s.%s", cphp_res_path, CPU_INSERT_EVENT);
> >           Aml *rm_evt = aml_name("%s.%s", cphp_res_path, CPU_REMOVE_EVENT);
> >           Aml *ej_evt = aml_name("%s.%s", cphp_res_path, CPU_EJECT_EVENT);
> > +        Aml *fw_ej_evt = aml_name("%s.%s", cphp_res_path, CPU_FW_EJECT_EVENT);
> >   
> >           aml_append(cpus_dev, aml_name_decl("_HID", aml_string("ACPI0010")));
> >           aml_append(cpus_dev, aml_name_decl("_CID", aml_eisaid("PNP0A05")));
> > @@ -461,7 +469,13 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
> >   
> >               aml_append(method, aml_acquire(ctrl_lock, 0xFFFF));
> >               aml_append(method, aml_store(idx, cpu_selector));
> > -            aml_append(method, aml_store(one, ej_evt));
> > +            if (opts.fw_unplugs_cpu) {
> > +                aml_append(method, aml_store(one, fw_ej_evt));
> > +                aml_append(method, aml_store(aml_int(OVMF_CPUHP_SMI_CMD),
> > +                           aml_name("%s", opts.smi_path)));
> > +            } else {
> > +                aml_append(method, aml_store(one, ej_evt));
> > +            }  
> My knowledge of AML is rather rudimentary but this looks mostly reasonable to me.
> 
> One question: the corresponding code for CPU hotplug does not send an SMI_CMD.
> Why the difference?
SMI for hotplug is sent during CSCN time before OSPM gets notification about new CPU[s]
it's a block below 'in case FW negotiated ICH9_LPC_SMI_F_CPU_HOTPLUG_BIT,' comment.

> 
>                      aml_append(while_ctx,
>                          aml_store(aml_derefof(aml_index(new_cpus, cpu_idx)),
>                                    uid));
>                      aml_append(while_ctx,
>                          aml_call2(CPU_NOTIFY_METHOD, uid, dev_chk));
>                      aml_append(while_ctx, aml_store(uid, cpu_selector));
>                      aml_append(while_ctx, aml_store(one, ins_evt));
>                      aml_append(while_ctx, aml_increment(cpu_idx));
> 
> 
> >               aml_append(method, aml_release(ctrl_lock));
> >           }
> >           aml_append(cpus_dev, method);
> > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > index 1f5c211245..475e76f514 100644
> > --- a/hw/i386/acpi-build.c
> > +++ b/hw/i386/acpi-build.c
> > @@ -96,6 +96,7 @@ typedef struct AcpiPmInfo {
> >       bool s4_disabled;
> >       bool pcihp_bridge_en;
> >       bool smi_on_cpuhp;
> > +    bool smi_on_cpu_unplug;
> >       bool pcihp_root_en;
> >       uint8_t s4_val;
> >       AcpiFadtData fadt;
> > @@ -197,6 +198,7 @@ static void acpi_get_pm_info(MachineState *machine, AcpiPmInfo *pm)
> >       pm->pcihp_io_base = 0;
> >       pm->pcihp_io_len = 0;
> >       pm->smi_on_cpuhp = false;
> > +    pm->smi_on_cpu_unplug = false;
> >   
> >       assert(obj);
> >       init_common_fadt_data(machine, obj, &pm->fadt);
> > @@ -220,6 +222,8 @@ static void acpi_get_pm_info(MachineState *machine, AcpiPmInfo *pm)
> >           pm->cpu_hp_io_base = ICH9_CPU_HOTPLUG_IO_BASE;
> >           pm->smi_on_cpuhp =
> >               !!(smi_features & BIT_ULL(ICH9_LPC_SMI_F_CPU_HOTPLUG_BIT));
> > +        pm->smi_on_cpu_unplug =
> > +            !!(smi_features & BIT_ULL(ICH9_LPC_SMI_F_CPU_HOT_UNPLUG_BIT));
> >       }
> >   
> >       /* The above need not be conditional on machine type because the reset port
> > @@ -1582,6 +1586,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
> >           CPUHotplugFeatures opts = {
> >               .acpi_1_compatible = true, .has_legacy_cphp = true,
> >               .smi_path = pm->smi_on_cpuhp ? "\\_SB.PCI0.SMI0.SMIC" : NULL,
> > +            .fw_unplugs_cpu = pm->smi_on_cpu_unplug,
> >           };
> >           build_cpus_aml(dsdt, machine, opts, pm->cpu_hp_io_base,
> >                          "\\_SB.PCI0", "\\_GPE._E02");
> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > index 17b514d1da..2952a00fe6 100644
> > --- a/hw/i386/pc.c
> > +++ b/hw/i386/pc.c
> > @@ -99,6 +99,7 @@
> >   
> >   GlobalProperty pc_compat_5_1[] = {
> >       { "ICH9-LPC", "x-smi-cpu-hotplug", "off" },
> > +    { "ICH9-LPC", "x-smi-cpu-hotunplug", "off" },
> >   };
> >   const size_t pc_compat_5_1_len = G_N_ELEMENTS(pc_compat_5_1);
> >   
> > diff --git a/hw/isa/lpc_ich9.c b/hw/isa/lpc_ich9.c
> > index 087a18d04d..8c667b7166 100644
> > --- a/hw/isa/lpc_ich9.c
> > +++ b/hw/isa/lpc_ich9.c
> > @@ -770,7 +770,7 @@ static Property ich9_lpc_properties[] = {
> >       DEFINE_PROP_BIT64("x-smi-cpu-hotplug", ICH9LPCState, smi_host_features,
> >                         ICH9_LPC_SMI_F_CPU_HOTPLUG_BIT, true),
> >       DEFINE_PROP_BIT64("x-smi-cpu-hotunplug", ICH9LPCState, smi_host_features,
> > -                      ICH9_LPC_SMI_F_CPU_HOT_UNPLUG_BIT, false),
> > +                      ICH9_LPC_SMI_F_CPU_HOT_UNPLUG_BIT, true),
> >       DEFINE_PROP_END_OF_LIST(),
> >   };
> >   
> >   
> 
> Thanks for sending out the patch btw. This helped me crystallize some of the
> corresponding OVMF code.
> 
> Ankur
>