回复: [PATCH RFC V3 02/29] cpu-common: Add common CPU utility for possible vCPUs

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发件人: qemu-devel-bounces+liuping24=outlook.com@nongnu.org <qemu-devel-bounces+liuping24=outlook.com@nongnu.org> 代表 Gavin Shan <gshan@redhat.com>
发送时间: 2024年8月11日 21:59
收件人: Salil Mehta <salil.mehta@huawei.com>; qemu-devel@nongnu.org <qemu-devel@nongnu.org>; qemu-arm@nongnu.org <qemu-arm@nongnu.org>; mst@redhat.com <mst@redhat.com>
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主题: Re: [PATCH RFC V3 02/29] cpu-common: Add common CPU utility for possible vCPUs

 

On 6/14/24 9:36 AM, Salil Mehta 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          | 31 +++++++++++++++++++++++++
>   include/hw/core/cpu.h | 54 +++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 85 insertions(+)
>
> diff --git a/cpu-common.c b/cpu-common.c
> index ce78273af5..49d2a50835 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;
> @@ -107,6 +108,36 @@ 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;
> +}
> +
> +bool qemu_enabled_cpu(CPUState *cpu)
> +{
> +    return cpu && !cpu->disabled;
> +}
> +
> +uint64_t qemu_get_cpu_archid(int cpu_index)
> +{
> +    MachineState *ms = MACHINE(qdev_get_machine());
> +    const CPUArchIdList *possible_cpus = ms->possible_cpus;
> +
> +    assert((cpu_index >= 0) && (cpu_index < possible_cpus->len));
> +
> +    return possible_cpus->cpus[cpu_index].arch_id;
> +}
> +
>   CPUState *qemu_get_cpu(int index)
>   {
>       CPUState *cpu;
> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
> index 60b160d0b4..60b4778da9 100644
> --- a/include/hw/core/cpu.h
> +++ b/include/hw/core/cpu.h
> @@ -528,6 +528,18 @@ struct CPUState {
>       CPUPluginState *plugin_state;
>   #endif
>  
> +    /*
> +     * Some architectures do not allow the *presence* of vCPUs to be changed
> +     * after the guest has booted, based on information specified by the
> +     * VMM/firmware via ACPI MADT at boot time. Thus, to enable vCPU hotplug on
> +     * these architectures, possible vCPUs can have a CPUState object in a
> +     * 'disabled' state or may not have a CPUState object at all. This is
> +     * possible when vCPU hotplug is supported, and vCPUs are
> +     * 'yet-to-be-plugged' in the QOM or have been hot-unplugged. By default,
> +     * every CPUState is enabled across all architectures.
> +     */
> +    bool disabled;
> +

The information to determine vCPU's state has been distributed to two data structs:
MachineState::possible_cpus::cpus[] and CPUState. Why not just to maintain the vCPU's
state from MachineState::possible_cpus::cpus[]? For example, adding a new field, or
something similiar, to 'struct CPUArchId' as below.

typedef struct CPUArchId {
#define CPU_ARCH_ID_FLAG_PRESENT        (1 << 0)
#define CPU_ARCH_ID_FLAG_ENABLED        (1 << 1)
     uint32_t flags;
        :
} CPUArchId;

In order to determine if a CPUState instance is enabled or not. CPUState::cpu_index
is used as the index to MachineState::possible_cpus::cpus[]. The flags can be parsed
to determine the vCPU's state.

>       /* TODO Move common fields from CPUArchState here. */
>       int cpu_index;
>       int cluster_index;
> @@ -914,6 +926,48 @@ 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);
> +
> +/**
> + * qemu_get_cpu_archid:
> + * @cpu_index: possible vCPU for which arch-id needs to be retreived
> + *
> + * Fetches the vCPU arch-id from the present possible vCPUs.
> + *
> + * Returns: arch-id of the possible vCPU
> + */
> +uint64_t qemu_get_cpu_archid(int cpu_index);
> +
>   /**
>    * cpu_exists:
>    * @id: Guest-exposed CPU ID to lookup.

Thanks,
Gavin