Hi Igor,
> From: Igor Mammedov <imamm...@redhat.com>
> Sent: Friday, October 18, 2024 3:25 PM
> To: Salil Mehta <salil.me...@huawei.com>
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> Subject: Re: [PATCH V1 3/4] hw/acpi: Reflect ACPI vCPU {present,enabled}
> states in ACPI _STA.{PRES,ENA} Bits
>
> On Mon, 14 Oct 2024 20:22:04 +0100
> Salil Mehta <salil.me...@huawei.com> 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.
>
> given questionable future of is_present/is_enabled fields, it probably
> premature to review this part.
Sure, let us discuss the pain points.
> The only thing, I have to say here is repeating spec/doc update patch
> describing how it should work should come 1st, so that we could compare
> this impl. with it.
>From the user perspective, there should not be any change in how he
plug/unplugs the ARM vCPUs. This is a requirement, as we have to
assists folks who wants to migrate from x86 world to ARM world
seamlessly (without affecting performance parameters) and this
feature is one small part of that bigger effort.
> > 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));
> > + }
> > + aml_append(ifctx, else_ctx);
> > }
> > aml_append(method, ifctx);
> > aml_append(method, aml_release(ctrl_lock));
>
