Hi Gustavo,
> From: Gustavo Romero <gustavo.rom...@linaro.org>
> Sent: Monday, October 21, 2024 3:10 AM
> To: Salil Mehta <salil.me...@huawei.com>; qemu-devel@nongnu.org;
> qemu-...@nongnu.org; m...@redhat.com
>
> Hi Salil,
>
> On 10/14/24 16:22, Salil Mehta wrote:
> > Reflect the ACPI CPU hotplug `is_{present, enabled}` states in the
> > `_STA.PRES`
> > (presence) and `_STA.ENA` (enabled) bits when the guest kernel
> > evaluates the ACPI `_STA` method during initialization, as well as
> > when vCPUs are hot-plugged or hot-unplugged. The presence of
> unplugged
> > vCPUs may need to be deliberately
> > *simulated* at the ACPI level to maintain a *persistent* view of vCPUs
> > for the guest kernel.
> >
> > Signed-off-by: Salil Mehta <salil.me...@huawei.com>
> > ---
> > hw/acpi/cpu.c | 26 ++++++++++++++++++++++----
> > 1 file changed, 22 insertions(+), 4 deletions(-)
> >
> > diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c index
> > 700aa855e9..23ea2b9c70 100644
> > --- a/hw/acpi/cpu.c
> > +++ b/hw/acpi/cpu.c
> > @@ -63,10 +63,11 @@ static uint64_t cpu_hotplug_rd(void *opaque,
> hwaddr addr, unsigned size)
> > cdev = &cpu_st->devs[cpu_st->selector];
> > switch (addr) {
> > case ACPI_CPU_FLAGS_OFFSET_RW: /* pack and return is_* fields */
> > - val |= cdev->cpu ? 1 : 0;
> > + val |= cdev->is_enabled ? 1 : 0;
> > val |= cdev->is_inserting ? 2 : 0;
> > val |= cdev->is_removing ? 4 : 0;
> > val |= cdev->fw_remove ? 16 : 0;
> > + val |= cdev->is_present ? 32 : 0;
> > trace_cpuhp_acpi_read_flags(cpu_st->selector, val);
> > break;
> > case ACPI_CPU_CMD_DATA_OFFSET_RW:
> > @@ -376,6 +377,7 @@ const VMStateDescription vmstate_cpu_hotplug =
> {
> > #define CPU_REMOVE_EVENT "CRMV"
> > #define CPU_EJECT_EVENT "CEJ0"
> > #define CPU_FW_EJECT_EVENT "CEJF"
> > +#define CPU_PRESENT "CPRS"
> >
> > void build_cpus_aml(Aml *table, MachineState *machine,
> CPUHotplugFeatures opts,
> > build_madt_cpu_fn build_madt_cpu, hwaddr
> > base_addr, @@ -436,7 +438,9 @@ void build_cpus_aml(Aml *table,
> MachineState *machine, CPUHotplugFeatures opts,
> > aml_append(field, aml_named_field(CPU_EJECT_EVENT, 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(3));
> > + /* 1 if present, read only */
> > + aml_append(field, aml_named_field(CPU_PRESENT, 1));
> > + aml_append(field, aml_reserved_field(2));
> > aml_append(field, aml_named_field(CPU_COMMAND, 8));
> > aml_append(cpu_ctrl_dev, field);
> >
> > @@ -466,6 +470,7 @@ void build_cpus_aml(Aml *table, MachineState
> *machine, CPUHotplugFeatures opts,
> > Aml *ctrl_lock = aml_name("%s.%s", cphp_res_path, CPU_LOCK);
> > Aml *cpu_selector = aml_name("%s.%s", cphp_res_path,
> CPU_SELECTOR);
> > Aml *is_enabled = aml_name("%s.%s", cphp_res_path,
> > CPU_ENABLED);
> > + Aml *is_present = aml_name("%s.%s", cphp_res_path,
> > + CPU_PRESENT);
> > Aml *cpu_cmd = aml_name("%s.%s", cphp_res_path,
> CPU_COMMAND);
> > Aml *cpu_data = aml_name("%s.%s", cphp_res_path, CPU_DATA);
> > Aml *ins_evt = aml_name("%s.%s", cphp_res_path,
> > CPU_INSERT_EVENT); @@ -494,13 +499,26 @@ void build_cpus_aml(Aml
> *table, MachineState *machine, CPUHotplugFeatures opts,
> > {
> > Aml *idx = aml_arg(0);
> > Aml *sta = aml_local(0);
> > + Aml *ifctx2;
> > + Aml *else_ctx;
> >
> > aml_append(method, aml_acquire(ctrl_lock, 0xFFFF));
> > aml_append(method, aml_store(idx, cpu_selector));
> > aml_append(method, aml_store(zero, sta));
> > - ifctx = aml_if(aml_equal(is_enabled, one));
> > + ifctx = aml_if(aml_equal(is_present, one));
> > {
> > - aml_append(ifctx, aml_store(aml_int(0xF), sta));
> > + ifctx2 = aml_if(aml_equal(is_enabled, one));
> > + {
> > + /* cpu is present and enabled */
> > + aml_append(ifctx2, aml_store(aml_int(0xF), sta));
> > + }
> > + aml_append(ifctx, ifctx2);
> > + else_ctx = aml_else();
> > + {
> > + /* cpu is present but disabled */
> > + aml_append(else_ctx, aml_store(aml_int(0xD),
> > + sta));
>
> Here, the return value for _STA method is set to reflect the state of
> CPU_PRESENT and CPU_ENABLED fields. I can't see these two fields being
> mapped to AcpiCpuStatus.{is_present,is_enabled}. They look to be mapped
> to the MMIO region (base_addr), which doesn't mapped to AcpiCpuStatus
> afaics. So where CPU_PRESENT and CPU_ENABLED are set and where
> exactly they reside?
You don’t set _STA field from guest for CPUs. We only fetch values being
reflected by the VMM. In general, ACPI _STA method is for fetching status
of a device. Please check below:
https://uefi.org/specs/ACPI/6.5/06_Device_Configuration.html?highlight=_sta#sta-device-status
We are banking on below status bits:
Bit [0] - Set if the device is present.
Bit [1] - Set if the device is enabled and decoding its resources.
Hence, AcpiCpuStatus::(is_present, is_enabled} are set in the VMM
and their status is shared to the guest kernel when the ACPI _STA
method is evaluated by the OSPM.
Patch 3/4:
https://lore.kernel.org/qemu-devel/20241014192205.253479-4-salil.me...@huawei.com/
#HUNK
diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c
index 700aa855e9..23ea2b9c70 100644
--- a/hw/acpi/cpu.c
+++ b/hw/acpi/cpu.c
@@ -63,10 +63,11 @@ static uint64_t cpu_hotplug_rd(void *opaque, hwaddr addr,
unsigned size)
cdev = &cpu_st->devs[cpu_st->selector];---------> check this code excerpt
switch (addr) {
case ACPI_CPU_FLAGS_OFFSET_RW: /* pack and return is_* fields */
- val |= cdev->cpu ? 1 : 0;
+ val |= cdev->is_enabled ? 1 : 0;---------------> this change
val |= cdev->is_inserting ? 2 : 0;
val |= cdev->is_removing ? 4 : 0;
val |= cdev->fw_remove ? 16 : 0;
+ val |= cdev->is_present ? 32 : 0;-------------> and this change
trace_cpuhp_acpi_read_flags(cpu_st->selector, val);
break;
case ACPI_CPU_CMD_DATA_OFFSET_RW:
Thanks
>
>
> Cheers,
> Gustavo
>
> > + }
> > + aml_append(ifctx, else_ctx);
> > }
> > aml_append(method, ifctx);
> > aml_append(method, aml_release(ctrl_lock));
