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

[Peter Maydell]

On 23 October 2012 10:37, Avi Kivity <address@hidden> wrote:
> 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:
>>>> 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?

Unless the device we're emulating supports multiple in
parallel accesses (and I bet 99.9% of the devices we model
don't) then the memory framework needs to serialise the
loads/stores. Otherwise it's just going to be excessively
hard to write a reliable device model.

-- PMM