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

[Avi Kivity]

On 10/23/2012 07:52 AM, 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.

I forgot about that.

I propose that we merge without a fix.  Upstream is broken in the same
way; it won't deadlock but it will surely break in some other way if a
write can cause another write to be triggered to the same location.

When we gain more experience with fine-graining devices we can converge
on a good solution.

-- 
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