Re: [PATCH RFC V4 02/33] cpu-common: Add common CPU utility for possible vCPUs

[Miguel Luis <miguel.luis@oracle.com>]

Hi Salil,

> On 9 Oct 2024, at 03:17, Salil Mehta <salil.mehta@huawei.com> wrote:
> 
> This patch adds various utility functions that may be required to fetch or check
> the state of possible vCPUs. It also introduces the concept of *disabled* vCPUs,
> which are part of the *possible* vCPUs but are not enabled. This state will be
> used during machine initialization and later during the plugging or unplugging
> of vCPUs. We release the QOM CPU objects for all disabled vCPUs.
> 
> Co-developed-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> ---
> cpu-common.c          | 21 ++++++++++++++++++++
> include/hw/core/cpu.h | 46 +++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 67 insertions(+)
> 
> diff --git a/cpu-common.c b/cpu-common.c
> index 6b262233a3..4a446f6f7f 100644
> --- a/cpu-common.c
> +++ b/cpu-common.c
> @@ -24,6 +24,7 @@
> #include "sysemu/cpus.h"
> #include "qemu/lockable.h"
> #include "trace/trace-root.h"
> +#include "hw/boards.h"
> 
> QemuMutex qemu_cpu_list_lock;
> static QemuCond exclusive_cond;
> @@ -108,6 +109,26 @@ void cpu_list_remove(CPUState *cpu)
>     cpu_list_generation_id++;
> }
> 
> +CPUState *qemu_get_possible_cpu(int index)
> +{
> +    MachineState *ms = MACHINE(qdev_get_machine());
> +    const CPUArchIdList *possible_cpus = ms->possible_cpus;
> +
> +    assert((index >= 0) && (index < possible_cpus->len));
> +
> +    return CPU(possible_cpus->cpus[index].cpu);
> +}
> +
> +bool qemu_present_cpu(CPUState *cpu)
> +{
> +    return cpu;

I don’t feel qemu_present_cpu should be needed as cpus are implicitly present as
an initialization premise and arm/virt being the only user of this now.

Thanks
Miguel

> +}
> +
> +bool qemu_enabled_cpu(CPUState *cpu)
> +{
> +    return cpu && !cpu->disabled;
> +}
> +
> CPUState *qemu_get_cpu(int index)
> {
>     CPUState *cpu;
> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
> index 1c9c775df6..73a4e4cce1 100644
> --- a/include/hw/core/cpu.h
> +++ b/include/hw/core/cpu.h
> @@ -538,6 +538,20 @@ struct CPUState {
>     CPUPluginState *plugin_state;
> #endif
> 
> +    /*
> +     * In the guest kernel, the presence of vCPUs is determined by information
> +     * provided by the VMM or firmware via the ACPI MADT at boot time. Some
> +     * architectures do not allow modifications to this configuration after
> +     * the guest has booted. Therefore, for such architectures, hotpluggable
> +     * vCPUs are exposed by the VMM as not 'ACPI Enabled' to the kernel.
> +     * Within QEMU, such vCPUs (those that are 'yet-to-be-plugged' or have
> +     * been hot-unplugged) may either have a `CPUState` object in a 'disabled'
> +     * state or may not have a `CPUState` object at all.
> +     *
> +     * By default, `CPUState` objects are enabled across all architectures.
> +     */
> +    bool disabled;
> +
>     /* TODO Move common fields from CPUArchState here. */
>     int cpu_index;
>     int cluster_index;
> @@ -924,6 +938,38 @@ static inline bool cpu_in_exclusive_context(const CPUState *cpu)
>  */
> CPUState *qemu_get_cpu(int index);
> 
> +/**
> + * qemu_get_possible_cpu:
> + * @index: The CPUState@cpu_index value of the CPU to obtain.
> + *         Input index MUST be in range [0, Max Possible CPUs)
> + *
> + * If CPUState object exists,then it gets a CPU matching
> + * @index in the possible CPU array.
> + *
> + * Returns: The possible CPU or %NULL if CPU does not exist.
> + */
> +CPUState *qemu_get_possible_cpu(int index);
> +
> +/**
> + * qemu_present_cpu:
> + * @cpu: The vCPU to check
> + *
> + * Checks if the vCPU is amongst the present possible vcpus.
> + *
> + * Returns: True if it is present possible vCPU else false
> + */
> +bool qemu_present_cpu(CPUState *cpu);
> +
> +/**
> + * qemu_enabled_cpu:
> + * @cpu: The vCPU to check
> + *
> + * Checks if the vCPU is enabled.
> + *
> + * Returns: True if it is 'enabled' else false
> + */
> +bool qemu_enabled_cpu(CPUState *cpu);
> +
> /**
>  * cpu_exists:
>  * @id: Guest-exposed CPU ID to lookup.
> -- 
> 2.34.1
>