Re: [PATCH v4] i386: Add ratelimit for bus locks acquired in guest

[Eduardo Habkost]

On Fri, May 21, 2021 at 12:38:20PM +0800, Chenyi Qiang wrote:
[...]
> @@ -4222,6 +4247,15 @@ void kvm_arch_pre_run(CPUState *cpu, struct kvm_run 
> *run)
>      }
>  }
>  
> +static void kvm_rate_limit_on_bus_lock(void)
> +{
> +    uint64_t delay_ns = ratelimit_calculate_delay(&bus_lock_ratelimit_ctrl, 
> 1);
> +
> +    if (delay_ns) {
> +        g_usleep(delay_ns / SCALE_US);
> +    }
> +}
> +
>  MemTxAttrs kvm_arch_post_run(CPUState *cpu, struct kvm_run *run)
>  {
>      X86CPU *x86_cpu = X86_CPU(cpu);
> @@ -4237,6 +4271,9 @@ MemTxAttrs kvm_arch_post_run(CPUState *cpu, struct 
> kvm_run *run)
>      } else {
>          env->eflags &= ~IF_MASK;
>      }
> +    if (run->flags & KVM_RUN_X86_BUS_LOCK) {

Does the KVM API guarantee that KVM_RUN_X86_BUS_LOCK will never
be set if KVM_BUS_LOCK_DETECTION_EXIT isn't enabled?  (Otherwise
we risk crashing in ratelimit_calculate_delay() above if rate
limiting is disabled).

If that's guaranteed, the patch looks good to me now.

> +        kvm_rate_limit_on_bus_lock();
> +    }
>  
>      /* We need to protect the apic state against concurrent accesses from
>       * different threads in case the userspace irqchip is used. */
> @@ -4595,6 +4632,10 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run 
> *run)
>          ioapic_eoi_broadcast(run->eoi.vector);
>          ret = 0;
>          break;
> +    case KVM_EXIT_X86_BUS_LOCK:
> +        /* already handled in kvm_arch_post_run */
> +        ret = 0;
> +        break;
>      default:
>          fprintf(stderr, "KVM: unknown exit reason %d\n", run->exit_reason);
>          ret = -1;
> -- 
> 2.17.1
> 

-- 
Eduardo