On Thu, Dec 30, 2010 at 12:37:18PM +0200, Avi Kivity wrote: > On 12/30/2010 12:32 PM, Michael S. Tsirkin wrote: > >On Thu, Dec 30, 2010 at 11:30:12AM +0200, Avi Kivity wrote: > >> On 12/30/2010 09:47 AM, Michael S. Tsirkin wrote: > >> >I am not really suggesting this. What I say is PBA is unimplemented > >> >let us not commit to an interface yet. > >> > >> What happens to a guest that tries to use PBA? > >> It's a mandatory part of MSI-X, no? > > > >Yes. Unfortunately the pending bit is in fact a communication channel > >used for function specific purposes when mask bit is set, > >and 0 when unset. The spec even seems to *require* this use: > > > >I refer to this: > > > > For MSI and MSI-X, while a vector is masked, the function is prohibited > > from sending the associated message, and the function must set the > > associated Pending bit whenever the function would otherwise send the > > message. When software unmasks a vector whose associated Pending bit is > > set, the function must schedule sending the associated message, and > > clear the Pending bit as soon as the message has been sent. Note that > > clearing the MSI-X Function Mask bit may result in many messages needing > > to be sent. > > > > > > If a masked vector has its Pending bit set, and the associated > > underlying interrupt events are somehow satisfied (usually by software > > though the exact manner is function-specific), the function must clear > > the Pending bit, to avoid sending a spurious interrupt message later > > when software unmasks the vector. However, if a subsequent interrupt > > event occurs while the vector is still masked, the function must again > > set the Pending bit. > > > > > > Software is permitted to mask one or more vectors indefinitely, and > > service their associated interrupt events strictly based on polling > > their Pending bits. A function must set and clear its Pending bits as > > necessary to support this âpure pollingâ mode of operation. > > > >For assigned devices, supporting this would require > >that the mask bits on the device are set if the mask bit in > >guest is set (otherwise pending bits are disabled). > > Can't this be done by setting the real mask bit when the guest reads > the virtual pending bit, then reading the real pending bit? Function specific is function-specific, but most likely not, by that time the pending bit in the device might be clear: 'clear the Pending bit as soon as the message has been sent' > >Existing code does not support PBA in assigned devices, so at least it's > >not a regression there, and the virtio spec says nothing about this so > >we should be fine. > > Why isn't it subject to the pci spec? > > If an interrupt condition exits, the bit should be set. I wish. But this is not what the spec says above. It says if vector is unmasked, bit must be cleared. > -- > error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
