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

[Chenyi Qiang <chenyi.qiang@intel.com>]

On 5/28/2021 5:19 AM, Eduardo Habkost wrote:
> 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).
> 

Yes. KVM_RUN_X86_BUS_LOCK flag is set when bus lock VM exit happens. Bus 
lock VM exit is disabled by default and can only be enabled through the 
KVM_BUS_LOCK_DETECTION_EXIT capability.

> 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
>>
>