Re: [Xen-devel] Re: Losing PS/2 Interrupts

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 23.05.11 at 14:09, Thomas Goetz <tcgoetz@xxxxxxxxx> wrote:
> My assumption is that at the point that the i8042 driver reads the data 
> register a new interrupt happens. There is gap in time between when the data 
> register is read and when the event channel pending state is cleared. Since 
> the hypervisor ACKed the previous real interrupt before delivering it to the 
> guest, there is nothing to stop the i8042 device from interrupting 
> immediately after the data register is read. If it interrupt before the event 
> channel pending state is cleared, then it will not be delivered to the guest 

That would be a bug in the control flow then. In our (non-pvops)
kernel we make sure to clear the pending bit *before* calling
handle_irq() (and after masking the event channel), which clearly
is a requirement at least for edge triggered interrupts (not
necessarily before calling handle_irq(), but before calling the
device driver's handler, i.e. in chip->ack()).

Jan

> and the EOI mechanism will be set up, but I haven't found anything in that 
> that will set up a delayed delivery of the second interrupt.
> 
> In this situation the i8042 device has every reason to believe the second 
> interrupt will be delivered. The previous interrupt was received and handled. 
> Nothing is masked.
> 
> Am I missing something?
> 
> ---
> Tom Goetz
> tcgoetz@xxxxxxxxx 




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