[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 0/4] Fix device listener interface for PCI to PCI bridges
On Tue, Jun 09, 2015 at 10:58:26AM +0000, Paul Durrant wrote: > > -----Original Message----- > > From: Michael S. Tsirkin [mailto:mst@xxxxxxxxxx] > > Sent: 09 June 2015 11:52 > > To: Paul Durrant > > Cc: Don Slutz; qemu-devel@xxxxxxxxxx; xen-devel@xxxxxxxxxxxxx; Stefano > > Stabellini > > Subject: Re: [PATCH v2 0/4] Fix device listener interface for PCI to PCI > > bridges > > > > On Tue, Jun 09, 2015 at 09:18:49AM +0000, Paul Durrant wrote: > > > > -----Original Message----- > > > > From: Michael S. Tsirkin [mailto:mst@xxxxxxxxxx] > > > > Sent: 09 June 2015 10:13 > > > > To: Don Slutz > > > > Cc: qemu-devel@xxxxxxxxxx; xen-devel@xxxxxxxxxxxxx; Paul Durrant; > > > > Stefano Stabellini > > > > Subject: Re: [PATCH v2 0/4] Fix device listener interface for PCI to PCI > > bridges > > > > > > > > On Mon, Jun 08, 2015 at 05:18:48PM -0400, Don Slutz wrote: > > > > > changes v1 to v2: > > > > > Split v1 patch into 3. > > > > > > > > > > Added a BUG FIX patch (#1: "exec: Do not use MemoryRegion after > > > > > free"). > > > > > > > > > > Technically this bug fix should be a separate patch, however this > > > > > issue only seems to reproduce when this patch set is applied. > > > > > > > > > > > > > > > Michael S. Tsirkin: > > > > > "You need some other API that makes sense, probably PCI specific." > > > > > This is basically patch #2: "Extend device listener > > > > > interface..." > > > > > > > > > > "This is relying on undocumented assumptions and how specific > > > > > firmware works. There's nothing special about bus number 255, > > > > > and 0 is not very special either (except it happens to be the > > > > > reset value)." > > > > > Dropped all checking of 0 and 255. > > > > > > > > > > > > > > > Open question by Michael S. Tsirkin: > > > > > > > > > > >>>> On Thu, May 28, 2015 at 07:25:50AM -0400, Don Slutz wrote: > > > > > ... > > > > > >>>> It is not clear to me that the complexity of tracking bus > > > > > >>>> visibility make sense. Clearly you do. > > > > > >>> Well what was the point of the change? > > > > > > > > > > > > To get config cycles that are valid that you do not get today. > > > > > > > > > > > >>> If you don't care that we get irrelevant config cycles why not > > > > > >>> just send them all to QEMU? > > > > > >>> > > > > > > > > > > > > That would need to be answered by Paul Durrant and/or other > > people > > > > (see > > > > > > below) > > > > > > > > > > > > > > > > We could broadcast config space ioreqs to all emulators, the problem > > > > > is how do we know (in the case of a read) which emulator is actually > > > > > the one supplying the data? At some level Xen needs to know who is > > > > > implementing what. > > > > > > > > > > Paul Durrant > > > > > > > > Can irrelevant emulators all respond with some kind of nack? > > > > Xen would pick the one that did respond correctly. > > > > > > > > > > I guess that's possible if we add an extra bit to the ioreq_t, but QEMU > > would still need to know when to nack and when to ack. > > > > It's simple: ack if we find a device handling the specific BDF. > > The result would at least be contained. > > OTOH detecting master aborts in core is useful since it would > > let us implement error reporting correctly. > > > > > > > It's still much simpler if qemu updates Xen with exact set of (S)BDFs it's > > handling. > > > > > > Paul > > > > > > I suspect this calls for a bigger change, you need to re-scan > > all of the tree to detect visible devices. > > Maybe just write some xen-specific code to do this on each > > config access. > > Well, that's the thing really... what triggers the re-scan. Do we really need > to scan on each access or is there a way to know when the topology is > changed? Doing the former doesn't really sound wonderfully efficient and, if > the answer to the second is yes, then that's the time to update Xen with the > currently valid set of BDFs. > > Paul Several things can trigger a topology change. One other option is switching to a memory API for config accesses, then using a memory listener to detect topology changes. That would be a lot of work I'm afraid. -- MST _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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