Re: [PATCH] KVM: X86: expand ->arch.apic_arb_prio to u64

[Longpeng (Mike)]

On 2017/8/8 21:08, Paolo Bonzini wrote:

> On 08/08/2017 13:37, Longpeng(Mike) wrote:
>> Currently 'apic_arb_prio' is int32_t, it's too short for long
>> time running. In our environment, it overflowed and then the
>> UBSAN was angry:
>>
>> signed integer overflow:
>> 2147483647 + 1 cannot be represented in type 'int'
>> CPU: 22 PID: 31237 Comm: qemu-kvm Tainted: ...
>> ...
>> Call Trace:
>>  [<ffffffff81f030b6>] dump_stack+0x1e/0x20
>>  [<ffffffff81f03173>] ubsan_epilogue+0x12/0x55
>>  [<ffffffff81f04658>] handle_overflow+0x1ba/0x215
>>  [<ffffffff81f046dd>] __ubsan_handle_add_overflow+0x2a/0x31
>>  [<ffffffffa126cb1a>] __apic_accept_irq+0x57a/0x5d0 [kvm]
>>  [<ffffffffa126d14f>] kvm_apic_set_irq+0x9f/0xf0 [kvm]
>>  [<ffffffffa126db20>] kvm_irq_delivery_to_apic_fast+0x450/0x910 [kvm]
>>  [<ffffffffa127d8ea>] kvm_irq_delivery_to_apic+0xfa/0x7a0 [kvm]
>>  [<ffffffffa127e039>] kvm_set_msi+0xa9/0x100 [kvm]
>>  [<ffffffffa12871ed>] kvm_send_userspace_msi+0x14d/0x1f0 [kvm]
>>  [<ffffffffa11ed56e>] kvm_vm_ioctl+0x4ee/0xdd0 [kvm]
>> ...
>>
>> We expand it to u64, this is large enough. Suppose the vcpu receives
>> 1000 irqs per second, then it won't overflow in 584942417 years.
>> ( 18446744073709551615/1000/3600/24/365 = 584942417 )
> 
> Since you only look at the difference, changing it to uint32_t should be
> enough.


Hi Paolo,

I'm afraid uint32_t isn't enough. For 1000 irqs per second, it can only holds
49 days ( although the overflow won't cause any corruption ).

4294967295/1000/3600/24 = 49

> 
> Paolo
> 

> .
> 


-- 
Regards,
Longpeng(Mike)