Re: [PATCH 0/1] RFC: pcie: parital fix for missing unplug events

[Michael S. Tsirkin]

On Wed, Jul 22, 2020 at 07:17:21PM +0300, Maxim Levitsky wrote:
> As described in bugzilla #1854264 it is possible to plug
> a pcie device and then unplug it before the guest notices
> (has time to process the attention button press)
> 
> To partially fix this issue, detect and refuse the hotunplug event.
> 
> There are other ways to fix this, which is why I am sending this as RFC:
> 
> 1. Queue/remember the unplug event and fire it (press the attention button 
> again),
> when the guest clears its pending status.
> According to the spec this should cancel the hotplug event in the guest
> if done within 5 seconds (and I think that guest actually should wait 5 
> seconds
> after attention button is pressed before plugging in the device too to be 
> strictly
> up to the spec)
> 
> 2. Detect that device isn't yet powered on by the guest (for example
> checking the bus master bit) or check that attention button is still
> pressed and in this case just unplug the device immediately.

I think 2 or failing that 1 would be preferable.


> Best regards,
>       Maxim Levitsky
> 
> Maxim Levitsky (1):
>   pci/pcie: refuse another hotplug/unplug event if attention button is
>     pending
> 
>  hw/pci/pcie.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> -- 
> 2.26.2
>