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

[Igor Mammedov]

On Thu, 26 Nov 2020 13:46:32 +0100
Laszlo Ersek <lersek@redhat.com> wrote:

> On 11/26/20 11:24, Ankur Arora 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.  
> 
> See just below, in the cpu_hotplug_wr() hunk. When bit#4 is written --
> which happens through the ACPI code change --, fw_remove is inverted.
> 
> 
> > 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?  
> 
> "is_removing" is set directly in response to the device_del QMP command.
> That QMP command is asynchronous to the execution of the guest OS.

its removing is notification to OSPM, which is cleared when ACPI scans
for events if I'm not mistaken.


> 
> "fw_remove" is set (by virtue of inverting) by ACPI CEJ0, which is
> executed by the guest OS's ACPI interpreter, after the guest OS has
> de-scheduled all processes from the CPU being removed (= basically after
> the OS has willfully forgotten about the CPU).
> 
> Therefore, considering the bitmask (is_removing, fw_remove), three
> variations make sense:
> 
> #1 (is_removing=0, fw_remove=0) -- normal status; no unplug requested
> 
> #2 (is_removing=1, fw_remove=0) -- unplug requested via QMP, guest OS
>                                    is processing the request


> #3 (is_removing=1, fw_remove=1) -- guest OS removed all references from
>                                    the CPU, firmware is permitted /
>                                    required to forget about the CPU as
>                                    well, and then unplug the CP
shouldn't be possible

> 
> #4 (is_removing=1, fw_remove=0) -- fimware is about to unplug the CPU
ditto


> #5 (is_removing=0, fw_remove=0) -- firmware performing unplug
> 
> 
> The variation (is_removing=0, fw_remove=1) is invalid / unused.
>
> 
> The firmware may be investigating the CPU register block between steps
> #2 and #3 -- in other words, the firmware may see a CPU for which
> is_remove is set (unplug requested via QMP), but the OS has not vacated
> yet (fw_remove=0). In that case, the firmware must just skip the CPU --
> once the OS is done, it will set fw_remove too, and raise another SMI.
> 
> 
> > 
> >   
> >>           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?  
> 
> This code (on eject) is executing *after* the OS kernel has processed
> the event. But on hotplug, the ordering is different (it must be): in
> that case, the CSCN (scan) method first notifies the firmware, and then
> the OS.
> 
> Thanks
> Laszlo
> 
> > 
> >                     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
> >   
>