Re: [PATCH V13 1/8] accel/kvm: Extract common KVM vCPU {creation,parking} code

[Igor Mammedov]

On Fri, 7 Jun 2024 12:56:42 +0100
Salil Mehta <salil.mehta@huawei.com> wrote:

> KVM vCPU creation is done once during the vCPU realization when Qemu vCPU 
> thread
> is spawned. This is common to all the architectures as of now.
> 
> 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 as KVM doesn't
> support vCPU removal. Therefore, its representative KVM vCPU object/context in
> Qemu is parked.
> 
> Refactor architecture common logic so that some APIs could be reused by vCPU
> Hotplug code of some architectures likes ARM, Loongson etc. Update new/old 
> APIs
> with trace events. No functional change is intended here.
> 
> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Tested-by: Xianglai Li <lixianglai@loongson.cn>
> Tested-by: Miguel Luis <miguel.luis@oracle.com>
> Reviewed-by: Shaoqin Huang <shahuang@redhat.com>
> Reviewed-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
> Tested-by: Zhao Liu <zhao1.liu@intel.com>
> Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
> Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
> ---
>  accel/kvm/kvm-all.c    | 95 ++++++++++++++++++++++++++++--------------
>  accel/kvm/kvm-cpus.h   |  1 -
>  accel/kvm/trace-events |  5 ++-
>  include/sysemu/kvm.h   | 25 +++++++++++
>  4 files changed, 92 insertions(+), 34 deletions(-)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index c0be9f5eed..8f9128bb92 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -340,14 +340,71 @@ 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_unpark_vcpu(KVMState *s, unsigned long vcpu_id)
> +{
> +    struct KVMParkedVcpu *cpu;
> +    int kvm_fd = -ENOENT;
> +
> +    QLIST_FOREACH(cpu, &s->kvm_parked_vcpus, node) {
> +        if (cpu->vcpu_id == vcpu_id) {
> +            QLIST_REMOVE(cpu, node);
> +            kvm_fd = cpu->kvm_fd;
> +            g_free(cpu);
> +        }
> +    }
> +
> +    trace_kvm_unpark_vcpu(vcpu_id, kvm_fd > 0 ? "unparked" : "not found 
> parked");
> +
> +    return kvm_fd;
> +}
> +
> +int kvm_create_vcpu(CPUState *cpu)
> +{
> +    unsigned long vcpu_id = kvm_arch_vcpu_id(cpu);
> +    KVMState *s = kvm_state;
> +    int kvm_fd;
> +
> +    /* check if the KVM vCPU already exist but is parked */
> +    kvm_fd = kvm_unpark_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;
> +
> +    trace_kvm_create_vcpu(cpu->cpu_index, vcpu_id, kvm_fd);
> +
> +    return 0;
> +}

Is there any reason why you are embedding/hiding kvm_state in new API
instead of passing it as argument (all callers have it defined, so why not 
reuse that)?

otherwise patch lgtm 

> +
>  static int do_kvm_destroy_vcpu(CPUState *cpu)
>  {
>      KVMState *s = kvm_state;
>      long mmap_size;
> -    struct KVMParkedVcpu *vcpu = NULL;
>      int ret = 0;
>  
> -    trace_kvm_destroy_vcpu();
> +    trace_kvm_destroy_vcpu(cpu->cpu_index, kvm_arch_vcpu_id(cpu));
>  
>      ret = kvm_arch_destroy_vcpu(cpu);
>      if (ret < 0) {
> @@ -373,10 +430,7 @@ 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;
>  }
> @@ -389,24 +443,6 @@ void kvm_destroy_vcpu(CPUState *cpu)
>      }
>  }
>  
> -static int kvm_get_vcpu(KVMState *s, unsigned long vcpu_id)
> -{
> -    struct KVMParkedVcpu *cpu;
> -
> -    QLIST_FOREACH(cpu, &s->kvm_parked_vcpus, node) {
> -        if (cpu->vcpu_id == vcpu_id) {
> -            int kvm_fd;
> -
> -            QLIST_REMOVE(cpu, node);
> -            kvm_fd = cpu->kvm_fd;
> -            g_free(cpu);
> -            return kvm_fd;
> -        }
> -    }
> -
> -    return kvm_vm_ioctl(s, KVM_CREATE_VCPU, (void *)vcpu_id);
> -}
> -
>  int kvm_init_vcpu(CPUState *cpu, Error **errp)
>  {
>      KVMState *s = kvm_state;
> @@ -415,19 +451,14 @@ 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/kvm-cpus.h b/accel/kvm/kvm-cpus.h
> index ca40add32c..171b22fd29 100644
> --- a/accel/kvm/kvm-cpus.h
> +++ b/accel/kvm/kvm-cpus.h
> @@ -22,5 +22,4 @@ bool kvm_supports_guest_debug(void);
>  int kvm_insert_breakpoint(CPUState *cpu, int type, vaddr addr, vaddr len);
>  int kvm_remove_breakpoint(CPUState *cpu, int type, vaddr addr, vaddr len);
>  void kvm_remove_all_breakpoints(CPUState *cpu);
> -
>  #endif /* KVM_CPUS_H */
> diff --git a/accel/kvm/trace-events b/accel/kvm/trace-events
> index 681ccb667d..37626c1ac5 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, int kvm_fd) 
> "index: %d, id: %lu, kvm fd: %d"
> +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_unpark_vcpu(unsigned long arch_cpu_id, const char *msg) "id: %lu %s"
>  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"
> @@ -25,7 +29,6 @@ kvm_dirty_ring_reaper(const char *s) "%s"
>  kvm_dirty_ring_reap(uint64_t count, int64_t t) "reaped %"PRIu64" pages (took 
> %"PRIi64" us)"
>  kvm_dirty_ring_reaper_kick(const char *reason) "%s"
>  kvm_dirty_ring_flush(int finished) "%d"
> -kvm_destroy_vcpu(void) ""
>  kvm_failed_get_vcpu_mmap_size(void) ""
>  kvm_cpu_exec(void) ""
>  kvm_interrupt_exit_request(void) ""
> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index c31d9c7356..c4a914b3d8 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -313,6 +313,31 @@ int kvm_create_device(KVMState *s, uint64_t type, bool 
> test);
>   */
>  bool kvm_device_supported(int vmfd, uint64_t type);
>  
> +/**
> + * 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);
> +
> +/**
> + * kvm_unpark_vcpu - unpark QEMU KVM vCPU context
> + * @s: KVM State
> + * @vcpu_id: Architecture vCPU ID of the parked vCPU
> + *
> + * @returns: KVM fd
> + */
> +int kvm_unpark_vcpu(KVMState *s, unsigned long vcpu_id);
> +
>  /* Arch specific hooks */
>  
>  extern const KVMCapabilityInfo kvm_arch_required_capabilities[];