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

[Emanuele Giuseppe Esposito]

Am 02/12/2022 um 07:54 schrieb 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?

Yes, because we must prevent any vcpu from reading memslots while we are
updating them.

> 
>>      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;
>>      }
>