[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] evtchn: don't lose pending state if FIFO event array page is missing
On 18/10/13 15:41, Jan Beulich wrote: >>>> On 18.10.13 at 16:06, David Vrabel <david.vrabel@xxxxxxxxxx> wrote: >> From: David Vrabel <david.vrabel@xxxxxxxxxx> >> >> When the FIFO-based ABI is in use, if an event is bound when the >> corresponding event array page is missing any attempt to set the event >> pending will lose the event (because there is nowhere to write the >> pending state). >> >> This wasn't initially considered an issue because guests were expected >> to only bind events once they had expanded the event array, however: >> >> 1. A domain may start with events already bound (by the toolstack). > > But a domain wouldn't start in FIFO mode, would it? Yes, guests always start in 2-level mode, but if the guest doesn't unmask the events they should still be pending after switching to FIFO mode so must copy the pending bits from the 2-level array and set them pending in the into the FIFO event array (when the pages turn up). David >> 2. The guest does not know what the port number will be until the >> event is bound (it doesn't know how many already bound events there >> are), so it does not know how many event array pages are required. >> This makes it difficult to expand in advanced (the current Linux >> implementation expands after binding for example). >> >> To prevent pending events from being lost because there is no array >> page, temporarily store the pending state in evtchn->pending. When an >> array page is added, use this state to set the port as pending. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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