Re: [Xen-devel] [PATCH 2/2 V2] iommu/amd: Workaround for erratum 787

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.06.13 at 14:43, Tim Deegan <tim@xxxxxxx> wrote:
> How about:
>  write-to-clear status.pending
>  process the log
>  if (status.pending)
>     reschedule the tasklet
>  else
>     unmask the interrupt.

Actually, I don't think that's right: Clearing the pending bit with
the respective interrupt source disabled doesn't allow the
pending bit to become set again upon arrival of a new log entry,
and hence we might still be leaving entries unhandled for an
indefinite period of time. So I now think we need to do

  write-to-clear status.pending
  process the log
  unmask the interrupt
  process the log again
  if (status.pending)
     reschedule the tasklet

Of course we could skip the unmask and parse-again if the
interrupt wasn't masked in the first place, which is possible since
it gets masked only for any IOMMU that had its interrupt handler
executed before the tasklet gets busy on it.

Jan


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