Re: [PATCH V4 01/10] accel/kvm: Extract common KVM vCPU {creation,parking} code

[Gavin Shan]

Hi Salil,

On 10/10/23 06:35, Salil Mehta wrote:
> KVM vCPU creation is done once during the initialization of the VM when Qemu
> thread is spawned. This is common to all the architectures.
>
> Hot-unplug of vCPU results in destruction of the vCPU object in QOM but the
> corresponding KVM vCPU object in the Host KVM is not destroyed and its
> representative KVM vCPU object/context in Qemu is parked.
>
> Refactor common logic so that some APIs could be reused by vCPU Hotplug code.
>
> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> ---
>   accel/kvm/kvm-all.c    | 64 ++++++++++++++++++++++++++++++++----------
>   accel/kvm/trace-events |  4 +++
>   include/sysemu/kvm.h   | 16 +++++++++++
>   3 files changed, 69 insertions(+), 15 deletions(-)

With the following one comment addressed:

Reviewed-by: Gavin Shan <gshan@redhat.com>

> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index ff1578bb32..0dcaa15276 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -137,6 +137,7 @@ static QemuMutex kml_slots_lock;
>   #define kvm_slots_unlock()  qemu_mutex_unlock(&kml_slots_lock)
>   
>   static void kvm_slot_init_dirty_bitmap(KVMSlot *mem);
> +static int kvm_get_vcpu(KVMState *s, unsigned long vcpu_id);
>   
>   static inline void kvm_resample_fd_remove(int gsi)
>   {
> @@ -320,14 +321,53 @@ err:
>       return ret;
>   }
>   
> +void kvm_park_vcpu(CPUState *cpu)
> +{
> +    struct KVMParkedVcpu *vcpu;
> +
> +    trace_kvm_park_vcpu(cpu->cpu_index, kvm_arch_vcpu_id(cpu));
> +
> +    vcpu = g_malloc0(sizeof(*vcpu));
> +    vcpu->vcpu_id = kvm_arch_vcpu_id(cpu);
> +    vcpu->kvm_fd = cpu->kvm_fd;
> +    QLIST_INSERT_HEAD(&kvm_state->kvm_parked_vcpus, vcpu, node);
> +}
> +
> +int kvm_create_vcpu(CPUState *cpu)
> +{
> +    unsigned long vcpu_id = kvm_arch_vcpu_id(cpu);
> +    KVMState *s = kvm_state;
> +    int kvm_fd;
> +
> +    trace_kvm_create_vcpu(cpu->cpu_index, kvm_arch_vcpu_id(cpu));
> +
> +    /* check if the KVM vCPU already exist but is parked */
> +    kvm_fd = kvm_get_vcpu(s, vcpu_id);
> +    if (kvm_fd < 0) {
> +        /* vCPU not parked: create a new KVM vCPU */
> +        kvm_fd = kvm_vm_ioctl(s, KVM_CREATE_VCPU, vcpu_id);
> +        if (kvm_fd < 0) {
> +            error_report("KVM_CREATE_VCPU IOCTL failed for vCPU %lu", vcpu_id);
> +            return kvm_fd;
> +        }
> +    }
> +
> +    cpu->kvm_fd = kvm_fd;
> +    cpu->kvm_state = s;
> +    cpu->vcpu_dirty = true;
> +    cpu->dirty_pages = 0;
> +    cpu->throttle_us_per_full = 0;
> +
> +    return 0;
> +}
> +
>   static int do_kvm_destroy_vcpu(CPUState *cpu)
>   {
>       KVMState *s = kvm_state;
>       long mmap_size;
> -    struct KVMParkedVcpu *vcpu = NULL;
>       int ret = 0;
>   
> -    DPRINTF("kvm_destroy_vcpu\n");
> +    trace_kvm_destroy_vcpu(cpu->cpu_index, kvm_arch_vcpu_id(cpu));
>   
>       ret = kvm_arch_destroy_vcpu(cpu);
>       if (ret < 0) {
> @@ -353,10 +393,7 @@ static int do_kvm_destroy_vcpu(CPUState *cpu)
>           }
>       }
>   
> -    vcpu = g_malloc0(sizeof(*vcpu));
> -    vcpu->vcpu_id = kvm_arch_vcpu_id(cpu);
> -    vcpu->kvm_fd = cpu->kvm_fd;
> -    QLIST_INSERT_HEAD(&kvm_state->kvm_parked_vcpus, vcpu, node);
> +    kvm_park_vcpu(cpu);
>   err:
>       return ret;
>   }
> @@ -377,6 +414,8 @@ static int kvm_get_vcpu(KVMState *s, unsigned long vcpu_id)
>           if (cpu->vcpu_id == vcpu_id) {
>               int kvm_fd;
>   
> +            trace_kvm_get_vcpu(vcpu_id);
> +
>               QLIST_REMOVE(cpu, node);
>               kvm_fd = cpu->kvm_fd;
>               g_free(cpu);
> @@ -384,7 +423,7 @@ static int kvm_get_vcpu(KVMState *s, unsigned long vcpu_id)
>           }
>       }
>   
> -    return kvm_vm_ioctl(s, KVM_CREATE_VCPU, (void *)vcpu_id);
> +    return -ENOENT;
>   }
>   
>   int kvm_init_vcpu(CPUState *cpu, Error **errp)
> @@ -395,19 +434,14 @@ int kvm_init_vcpu(CPUState *cpu, Error **errp)
>   
>       trace_kvm_init_vcpu(cpu->cpu_index, kvm_arch_vcpu_id(cpu));
>   
> -    ret = kvm_get_vcpu(s, kvm_arch_vcpu_id(cpu));
> +    ret = kvm_create_vcpu(cpu);
>       if (ret < 0) {
> -        error_setg_errno(errp, -ret, "kvm_init_vcpu: kvm_get_vcpu failed 
> (%lu)",
> +        error_setg_errno(errp, -ret,
> +                         "kvm_init_vcpu: kvm_create_vcpu failed (%lu)",
>                            kvm_arch_vcpu_id(cpu));
>           goto err;
>       }
>   
> -    cpu->kvm_fd = ret;
> -    cpu->kvm_state = s;
> -    cpu->vcpu_dirty = true;
> -    cpu->dirty_pages = 0;
> -    cpu->throttle_us_per_full = 0;
> -
>       mmap_size = kvm_ioctl(s, KVM_GET_VCPU_MMAP_SIZE, 0);
>       if (mmap_size < 0) {
>           ret = mmap_size;
> diff --git a/accel/kvm/trace-events b/accel/kvm/trace-events
> index 399aaeb0ec..08e2dc253f 100644
> --- a/accel/kvm/trace-events
> +++ b/accel/kvm/trace-events
> @@ -9,6 +9,10 @@ kvm_device_ioctl(int fd, int type, void *arg) "dev fd %d, type 
> 0x%x, arg %p"
>   kvm_failed_reg_get(uint64_t id, const char *msg) "Warning: Unable to retrieve ONEREG %" 
> PRIu64 " from KVM: %s"
>   kvm_failed_reg_set(uint64_t id, const char *msg) "Warning: Unable to set ONEREG %" 
> PRIu64 " to KVM: %s"
>   kvm_init_vcpu(int cpu_index, unsigned long arch_cpu_id) "index: %d id: %lu"
> +kvm_create_vcpu(int cpu_index, unsigned long arch_cpu_id) "creating KVM cpu: 
> cpu_index: %d arch vcpu-id: %lu"
> +kvm_get_vcpu(unsigned long arch_cpu_id) "unparking KVM vcpu: arch vcpu-id: %lu"
> +kvm_destroy_vcpu(int cpu_index, unsigned long arch_cpu_id) "destroy vcpu: 
> cpu_index: %d arch vcpu-id: %lu"
> +kvm_park_vcpu(int cpu_index, unsigned long arch_cpu_id) "parking KVM vcpu: 
> cpu_index: %d arch vcpu-id: %lu"

I don't think we need the duplicate identifiers like "creating KVM cpu"
since the event name can serve the purpose. Besides, the parameters
are descriptive by "index: %d id: %lu", used by kvm_init_vcpu(). We just
need to follow that pattern. Otherwise, inconsistent output will be printed
by kvm_init_vcpu() and kvm_get_vcpu(). So I would change them like below:

kvm_init_vcpu(int cpu_index, unsigned long arch_cpu_id) "index: %d id: %lu"
kvm_create_vcpu(int cpu_index, unsigned long arch_cpu_id) "index: %d id: %lu"
kvm_get_vcpu(unsigned long arch_cpu_id) "id: %lu"
kvm_destroy_vcpu(int cpu_index, unsigned long arch_cpu_id) "index: %d id: %lu"
kvm_park_vcpu(int cpu_index, unsigned long arch_cpu_id) "index: %d id: %lu"

>   kvm_irqchip_commit_routes(void) ""
>   kvm_irqchip_add_msi_route(char *name, int vector, int virq) "dev %s vector %d virq 
> %d"
>   kvm_irqchip_update_msi_route(int virq) "Updating MSI route virq=%d"
> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index ee9025f8e9..740686ab60 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -465,6 +465,22 @@ void kvm_set_sigmask_len(KVMState *s, unsigned int 
> sigmask_len);
>   int kvm_physical_memory_addr_from_host(KVMState *s, void *ram_addr,
>                                          hwaddr *phys_addr);
>   
> +/**
> + * kvm_create_vcpu - Gets a parked KVM vCPU or creates a KVM vCPU
> + * @cpu: QOM CPUState object for which KVM vCPU has to be fetched/created.
> + *
> + * @returns: 0 when success, errno (<0) when failed.
> + */
> +int kvm_create_vcpu(CPUState *cpu);
> +
> +/**
> + * kvm_park_vcpu - Park Qemu KVM vCPU context
> + * @cpu: QOM CPUState object for which Qemu KVM vCPU context has to be parked.
> + *
> + * @returns: none
> + */
> +void kvm_park_vcpu(CPUState *cpu);
> +
>   #endif /* NEED_CPU_H */
>   
>   void kvm_cpu_synchronize_state(CPUState *cpu);

Thanks,
Gavin