Hi Gavin,
> From: Gavin Shan <gs...@redhat.com>
> Sent: Wednesday, September 27, 2023 7:29 AM
> To: Salil Mehta <salil.me...@huawei.com>; qemu-devel@nongnu.org; qemu-
> a...@nongnu.org
> Cc: m...@kernel.org; jean-phili...@linaro.org; Jonathan Cameron
> <jonathan.came...@huawei.com>; lpieral...@kernel.org;
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> il...@os.amperecomputing.com; vis...@os.amperecomputing.com;
> karl.heub...@oracle.com; miguel.l...@oracle.com; salil.me...@opnsrc.net;
> zhukeqian <zhukeqi...@huawei.com>; wangxiongfeng (C)
> <wangxiongfe...@huawei.com>; wangyanan (Y) <wangyana...@huawei.com>;
> jiakern...@gmail.com; maob...@loongson.cn; lixiang...@loongson.cn
> Subject: Re: [PATCH RFC V2 04/37] arm/virt,target/arm: Machine init time
> change common to vCPU {cold|hot}-plug
>
> Hi Salil,
>
> On 9/26/23 20:04, Salil Mehta wrote:
> > Refactor and introduce the common logic required during the
> initialization of
> > both cold and hot plugged vCPUs. Also initialize the *disabled* state of the
> > vCPUs which shall be used further during init phases of various other
> > components
> > like GIC, PMU, ACPI etc as part of the virt machine initialization.
> >
> > KVM vCPUs corresponding to unplugged/yet-to-be-plugged QOM CPUs are kept in
> > powered-off state in the KVM Host and do not run the guest code. Plugged
> > vCPUs
> > are also kept in powered-off state but vCPU threads exist and is kept
> > sleeping.
> >
> > TBD:
> > For the cold booted vCPUs, this change also exists in the arm_load_kernel()
> > in boot.c but for the hotplugged CPUs this change should still remain part
> > of
> > the pre-plug phase. We are duplicating the powering-off of the cold booted
> > CPUs.
> > Shall we remove the duplicate change from boot.c?
> >
> > Co-developed-by: Salil Mehta <salil.me...@huawei.com>
> > Signed-off-by: Salil Mehta <salil.me...@huawei.com>
> > Co-developed-by: Keqian Zhu <zhukeqi...@huawei.com>
> > Signed-off-by: Keqian Zhu <zhukeqi...@huawei.com>
> > Reported-by: Gavin Shan <gavin.s...@redhat.com>
> > [GS: pointed the assertion due to wrong range check]
> > Signed-off-by: Salil Mehta <salil.me...@huawei.com>
> > ---
> > hw/arm/virt.c | 149 ++++++++++++++++++++++++++++++++++++++++-----
> > target/arm/cpu.c | 7 +++
> > target/arm/cpu64.c | 14 +++++
> > 3 files changed, 156 insertions(+), 14 deletions(-)
> >
> > diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> > index 0eb6bf5a18..3668ad27ec 100644
> > --- a/hw/arm/virt.c
> > +++ b/hw/arm/virt.c
> > @@ -221,6 +221,7 @@ static const char *valid_cpus[] = {
> > ARM_CPU_TYPE_NAME("max"),
> > };
> >
> > +static CPUArchId *virt_find_cpu_slot(MachineState *ms, int vcpuid);
> > static int virt_get_socket_id(const MachineState *ms, int cpu_index);
> > static int virt_get_cluster_id(const MachineState *ms, int cpu_index);
> > static int virt_get_core_id(const MachineState *ms, int cpu_index);
> > @@ -2154,6 +2155,14 @@ static void machvirt_init(MachineState *machine)
> > exit(1);
> > }
> >
> > + finalize_gic_version(vms);
> > + if (tcg_enabled() || hvf_enabled() || qtest_enabled() ||
> > + (vms->gic_version < VIRT_GIC_VERSION_3)) {
> > + machine->smp.max_cpus = smp_cpus;
> > + mc->has_hotpluggable_cpus = false;
> > + warn_report("cpu hotplug feature has been disabled");
> > + }
> > +
>
> Comments needed here to explain why @mc->has_hotpluggable_cpus is set to
> false.
> I guess it's something related to TODO list, mentioned in the cover letter.
I can put a comment explaining the checks as to why feature has been disabled.
BTW, isn't code self-explanatory here?
[...]
> > +static CPUArchId *virt_find_cpu_slot(MachineState *ms, int vcpuid)
> > +{
> > + VirtMachineState *vms = VIRT_MACHINE(ms);
> > + CPUArchId *found_cpu;
> > + uint64_t mp_affinity;
> > +
> > + assert(vcpuid >= 0 && vcpuid < ms->possible_cpus->len);
> > +
> > + /*
> > + * RFC: Question:
> > + * TBD: Should mp-affinity be treated as MPIDR?
> > + */
> > + mp_affinity = virt_cpu_mp_affinity(vms, vcpuid);
> > + found_cpu = &ms->possible_cpus->cpus[vcpuid];
> > +
> > + assert(found_cpu->arch_id == mp_affinity);
> > +
> > + /*
> > + * RFC: Question:
> > + * Slot-id is the index where vCPU with certain
> > arch-id(=mpidr/ap-affinity)
> > + * is plugged. For Host KVM, MPIDR for vCPU is derived using vcpu-id.
> > + * As I understand, MPIDR and vcpu-id are property of vCPU but slot-id
> > is
> > + * more related to machine? Current code assumes slot-id and vcpu-id
> > are
> > + * same i.e. meaning of slot is bit vague.
> > + *
> > + * Q1: Is there any requirement to clearly represent slot and
> > dissociate it
> > + * from vcpu-id?
> > + * Q2: Should we make MPIDR within host KVM user configurable?
> > + *
> > + * +----+----+----+----+----+----+----+----+
> > + * MPIDR ||| Res | Aff2 | Aff1 | Aff0 |
> > + * +----+----+----+----+----+----+----+----+
> > + * \ \ \ | |
> > + * \ 8bit \ 8bit \ |4bit|
> > + * \<------->\<------->\ |<-->|
> > + * \ \ \| |
> > + * +----+----+----+----+----+----+----+----+
> > + * VCPU-ID | Byte4 | Byte2 | Byte1 | Byte0 |
> > + * +----+----+----+----+----+----+----+----+
> > + */
> > +
> > + return found_cpu;
> > +}
> > +
>
> MPIDR[31] is set to 0b1, looking at
> linux/arch/arm64/kvm/sys_regs.c::reset_mpidr().
>
> I think this function can be renamed to virt_get_cpu_slot(ms, index), better
> to
> reflect its intention. I had same concerns why cs->cpu_index can't be
> reused as MPIDR, but it's out of scope for this series. It maybe something to
> be
> improved afterwards.
Yes, right now it is linear mapping but this might change. I would suggest to
keep
it like this with a comment so that it can be addressed in future.
User configurability of the MPIDR is not in the scope of this patch. Agreed.
[...]
> > +static void virt_cpu_pre_plug(HotplugHandler *hotplug_dev, DeviceState
> *dev,
> > + Error **errp)
> > +{
> > + VirtMachineState *vms = VIRT_MACHINE(hotplug_dev);
> > + MachineState *ms = MACHINE(hotplug_dev);
> > + ARMCPU *cpu = ARM_CPU(dev);
> > + CPUState *cs = CPU(dev);
> > + CPUArchId *cpu_slot;
> > + int32_t min_cpuid = 0;
> > + int32_t max_cpuid;
> > +
> > + /* sanity check the cpu */
> > + if (!object_dynamic_cast(OBJECT(cpu), ms->cpu_type)) {
> > + error_setg(errp, "Invalid CPU type, expected cpu type: '%s'",
> > + ms->cpu_type);
> > + return;
> > + }
> > +
> > + if ((cpu->thread_id < 0) || (cpu->thread_id >= ms->smp.threads)) {
> > + error_setg(errp, "Invalid thread-id %u specified, correct range
> 0:%u",
> > + cpu->thread_id, ms->smp.threads - 1);
> > + return;
> > + }
> > +
> > + max_cpuid = ms->possible_cpus->len - 1;
> > + if (!dev->hotplugged) {
> > + min_cpuid = vms->acpi_dev ? ms->smp.cpus : 0;
> > + max_cpuid = vms->acpi_dev ? max_cpuid : ms->smp.cpus - 1;
> > + }
> > +
>
> I don't understand how the range is figured out. cpu->core_id should
> be in range [0, ms->smp.cores).
> With your code, the following scenario
> becomes invalid incorrectly?
>
> -cpu host -smp maxcpus=4,cpus=1,sockets=4,clusters=1,cores=1,threads=1
Ghosh. I am not sure what I was thinking while I added this.
Whatever maybe your circumstances never drink and code. Deadly
combination! (Repeat offender)
Will correct this.
Thanks
Salil.
[...]
> > +
> > +static void virt_cpu_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
> > + Error **errp)
> > +{
> > + MachineState *ms = MACHINE(hotplug_dev);
> > + CPUState *cs = CPU(dev);
> > + CPUArchId *cpu_slot;
> > +
> > + /* insert the cold/hot-plugged vcpu in the slot */
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> May be:
>
> /* CPU becomes present */
Not exactly. In this leg CPU is being plugged by user action or during
init time. After plugging action is complete, a CPU eventually becomes
present.
>
> > + cpu_slot = virt_find_cpu_slot(ms, cs->cpu_index);
> > + cpu_slot->cpu = OBJECT(dev);
> > +
> > + cs->disabled = false;
> > + return;
> ^^^^^^
>
> not needed.
Agreed.
>
> May be worthy some comments like below, correlating to what's done in
> aarch64_cpu_initfn():
>
> /* CPU becomes enabled after it's hot added */
I can add a line over the initialization, if thats what you mean?
>
> > +}
> > +
> > static void virt_machine_device_pre_plug_cb(HotplugHandler
> *hotplug_dev,
> > DeviceState *dev, Error
> **errp)
[...]
> > +static void aarch64_cpu_initfn(Object *obj)
> > +{
> > + CPUState *cs = CPU(obj);
> > +
> > + /*
> > + * we start every ARM64 vcpu as disabled possible vCPU. It needs to
> be
> > + * enabled explicitly
> > + */
> > + cs->disabled = true;
> > +}
> > +
>
> The comments can be simplified to:
>
> /* The CPU state isn't enabled until it's hot added completely */
There is a reason why I have added comment that way because for
other architectures 'disabled' would be false by default.
> > static void aarch64_cpu_finalizefn(Object *obj)
> > {
> > }
> > @@ -751,7 +762,9 @@ static gchar *aarch64_gdb_arch_name(CPUState *cs)
> > static void aarch64_cpu_class_init(ObjectClass *oc, void *data)
> > {
> > CPUClass *cc = CPU_CLASS(oc);
> > + DeviceClass *dc = DEVICE_CLASS(oc);
> >
> > + dc->user_creatable = true;
> > cc->gdb_read_register = aarch64_cpu_gdb_read_register;
> > cc->gdb_write_register = aarch64_cpu_gdb_write_register;
> > cc->gdb_num_core_regs = 34;
> > @@ -800,6 +813,7 @@ static const TypeInfo aarch64_cpu_type_info = {
> > .name = TYPE_AARCH64_CPU,
> > .parent = TYPE_ARM_CPU,
> > .instance_size = sizeof(ARMCPU),
> > + .instance_init = aarch64_cpu_initfn,
> > .instance_finalize = aarch64_cpu_finalizefn,
> > .abstract = true,
> > .class_size = sizeof(AArch64CPUClass),
>
> I'm not sure if 'dc->user_creatable' can be set true here because
> the ARMCPU objects aren't ready for hot added/removed at this point.
> The hacks for GICv3 aren't included so far. I think a separate patch
> may be needed in the last to enable the functionality?
This patch contains common init time changes for CPU {hot,cold} plug.
Thanks
Salil.
