Re: [PATCH v3 2/3] KVM: keep track of running ioctls

[Robert Hoo]

On Fri, 2022-11-11 at 10:47 -0500, Emanuele Giuseppe Esposito wrote:
> Using the new accel-blocker API, mark where ioctls are being called
> in KVM. Next, we will implement the critical section that will take
> care of performing memslots modifications atomically, therefore
> preventing any new ioctl from running and allowing the running ones
> to finish.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  accel/kvm/kvm-all.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index f99b0becd8..ff660fd469 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -2310,6 +2310,7 @@ static int kvm_init(MachineState *ms)
>      assert(TARGET_PAGE_SIZE <= qemu_real_host_page_size());
>  
>      s->sigmask_len = 8;
> +    accel_blocker_init();
>  
>  #ifdef KVM_CAP_SET_GUEST_DEBUG
>      QTAILQ_INIT(&s->kvm_sw_breakpoints);
> @@ -3014,7 +3015,9 @@ int kvm_vm_ioctl(KVMState *s, int type, ...)
>      va_end(ap);
>  
>      trace_kvm_vm_ioctl(type, arg);
> +    accel_ioctl_begin();
>      ret = ioctl(s->vmfd, type, arg);
> +    accel_ioctl_end();
>      if (ret == -1) {
>          ret = -errno;
>      }
> @@ -3032,7 +3035,9 @@ int kvm_vcpu_ioctl(CPUState *cpu, int type,
> ...)
>      va_end(ap);
>  
>      trace_kvm_vcpu_ioctl(cpu->cpu_index, type, arg);
> +    accel_cpu_ioctl_begin(cpu);

Does this mean that kvm_region_commit() can inhibit any other vcpus
doing any ioctls?

>      ret = ioctl(cpu->kvm_fd, type, arg);
> +    accel_cpu_ioctl_end(cpu);
>      if (ret == -1) {
>          ret = -errno;
>      }
> @@ -3050,7 +3055,9 @@ int kvm_device_ioctl(int fd, int type, ...)
>      va_end(ap);
>  
>      trace_kvm_device_ioctl(fd, type, arg);
> +    accel_ioctl_begin();
>      ret = ioctl(fd, type, arg);
> +    accel_ioctl_end();
>      if (ret == -1) {
>          ret = -errno;
>      }