Re: [Qemu-devel] [patch v4 13/16] e1000: add busy flag to anti broken device state

[Avi Kivity]

On 10/23/2012 11:32 AM, liu ping fan wrote:
> On Tue, Oct 23, 2012 at 5:07 PM, Jan Kiszka <address@hidden> wrote:
>> On 2012-10-23 07:52, liu ping fan wrote:
>>> On Mon, Oct 22, 2012 at 6:40 PM, Avi Kivity <address@hidden> wrote:
>>>> On 10/22/2012 11:23 AM, Liu Ping Fan wrote:
>>>>> The broken device state is caused by releasing local lock before acquiring
>>>>> big lock. To fix this issue, we have two choice:
>>>>>   1.use busy flag to protect the state
>>>>>     The drawback is that we will introduce independent busy flag for each
>>>>>     independent device's logic unit.
>>>>>   2.reload the device's state
>>>>>     The drawback is if the call chain is too deep, the action to reload 
>>>>> will
>>>>>     touch each layer. Also the reloading means to recaculate the 
>>>>> intermediate
>>>>>     result based on device's regs.
>>>>>
>>>>> This patch adopt the solution 1 to fix the issue.
>>>>
>>>> Doesn't the nested mmio patch detect this?
>>>>
>>> It will only record and fix the issue on one thread. But guest can
>>> touch the emulated device on muti-threads.
>>
>> Sorry, what does that mean? A second VCPU accessing the device will
>> simply be ignored when it races with another VCPU? Specifically
>>
> Yes, just ignored.  For device which support many logic in parallel,
> it should use independent busy flag for each logic

We don't actually know that e1000 doesn't.  Why won't writing into
different registers in parallel work?


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