Re: [RFC PATCH 3/4] KVM: stats: Add ioctl commands to pull statistics in binary format

On 10/03/21 16:51, Marc Zyngier wrote:

...

• kvm_for_each_vcpu(j, vcpu, kvm) {

• pdata = data + VM_STAT_COUNT;
  

• for (i = 0; i < VCPU_STAT_COUNT; i++, pdata++)
  

• 	*pdata += *((u64 *)&vcpu->stat + i);
  

Do you really need the in-kernel copy? Why not directly organise the data structures in a way that would allow a bulk copy using copy_to_user()?

The result is built by summing per-vCPU counters, so that the counter updates are fast and do not require a lock. So consistency basically cannot be guaranteed.

Paolo