Re: [PATCH] x86: ioapic needs check attr when programmed more than once

[Liu ping fan]

On Fri, Aug 23, 2013 at 4:04 PM, Liu ping fan <kernelfans@xxxxxxxxx> wrote:
> On Fri, Aug 23, 2013 at 3:30 PM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>>
>> * Liu Ping Fan <kernelfans@xxxxxxxxx> wrote:
>>
>>> When programming ioapic pinX more than once, current code
>>> does not check whether the later attr (trigger&polarity) is the
>>> same as the former or not. This causes a broken semantic.
>>>
>>> Fix it by reporting -EBUSY, when attr is different.
>>
>> Was this observed in real life somehow, and if yes, what is
>> the before/after behavior?
>>
> Using qemu q35 machine, I found the ioapic's ioredtbl[] will never has
> low-active, even the hpet driver registered it. After tracing, I found
> it shared a high-level active IRQ line with other device. So in fact,
> the acpi_register_gsi(, ACPI_ACTIVE_LOW) in hpet driver fail, but it
> did not detect it.
> The effect in qemu: when hpet-dev assert low-level, the kernel can not respond.
>
After changing, I can observe the low-active be set in ioredtbl[x],
and with some bug fix in qemu's hpet, the kernel can work.
>
> Thanks,
> Pingfan
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