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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Question about the XEN platform pci
On Wed, Apr 13, 2016 at 11:55 AM, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote: > On Wed, Apr 13, 2016 at 09:00:18AM +0200, karim.allah.ahmed@xxxxxxxxx wrote: >> On Tue, Apr 12, 2016 at 5:45 PM, Konrad Rzeszutek Wilk >> <konrad.wilk@xxxxxxxxxx> wrote: >> > On Tue, Apr 12, 2016 at 05:33:47PM +0200, karim.allah.ahmed@xxxxxxxxx >> > wrote: >> >> The INTx interrupt of this platform device can be used by Xen in HVM case >> >> to >> >> notify the guest of pending events in the event channel. However that's >> >> usually >> >> not used in favor of vector callbacks support in Xen where a vector is >> >> injected >> >> directly to the vCPU bypassing LAPIC. >> >> >> >> (that said, the platform-pci driver in linux is actually broken when >> >> vector >> >> callbacks are not used anyway) >> > >> > Oh? Is there an report/bug somewhere? >> > >> >> I'm not sure if it's reported as a bug somewhere or not. >> >> I've always assumed that INTx is deperecated and vector callbacks are the one >> that's supported that's why I never tried to fix it, in addition I never >> tried >> to reproduce it I just looked at the code and it seemed a little bit off as >> explained below. >> >> Mainly xenbus_init is called during postcore_initcall which will eventually >> try >> to read a value from XenStore and will get stuck on read_reply at xenbus >> forever since the platform driver is not probed yet and its INTx interrupt >> handler is not registered yet which basically means that the guest can not be >> notified at this moment of any pending event channels and none of the >> per-event >> handlers will ever be invoked (including the XenStore one) and the reply will >> never be picked up by the kernel. > > Argh, well that is not good. Also - thanks for reporting this. > > No simple ideas come to my mind on how this can be fixed - unless we > move the xenbus_init and its driver past the platform-pci init? > > Or if platform-pci init code ends up being called earlier? > Let me test a few alternatives and send a patch to fix that first. >> >> The exact stack where things get stuck during xenbus_init: >> >> -xenbus_init >> -xs_init >> -xs_reset_watches >> -xenbus_scanf >> -xenbus_read >> -xs_single >> -xs_single >> -xs_talkv >> >> > Thanks! >> >> >> >> I also think that the grant-table lives on this PCI device MMIO BAR (?!) >> > >> > The area may be usurped for grant-table as the OS won't touch that memory >> > area (it after all belongs to the device). >> >> >> >> If you looked at hw/i386/xen/xen_platform.c in QEMU source , you will get >> >> a >> >> general idea what this device is supposed todo (like logging to syslog >> >> stuff >> >> for example). >> >> >> >> That said the platform device is really not fully utilized anyway in >> >> Linux. >> >> >> >> On Tue, Apr 12, 2016 at 4:09 PM, Konrad Rzeszutek Wilk >> >> <konrad.wilk@xxxxxxxxxx> wrote: >> >> > On Tue, Apr 12, 2016 at 02:19:48AM +0000, Wu, Bob wrote: >> >> >> >> >> >> Really thanks for your reply. >> >> > >> >> > Hey! >> >> > >> >> > CC-ing Xen-devel back on. Please do not drop it and please don't >> >> > top-post. >> >> >> >> >> >> Can you explain a little more? >> >> > >> >> > I am not sure what you want me to explain. Perhaps if you >> >> > read http://xenbits.xen.org/docs/unstable/misc/hvm-emulated-unplug.html >> >> > it may become clearer? >> >> > >> >> >> Is the xen platform pci driver the only purpose for telling QEMU that >> >> >> don’t emulate the IDE driver? >> >> > >> >> > And network. >> >> >> I think it can be done by a simple way, but don't need use this huge >> >> >> platform driver. >> >> > >> >> > ? >> >> >> >> >> >> I guess this is for PCI pass through in XEN HVM mode, but don't sure. >> >> > >> >> > No. >> >> >> >> >> >> Thanks, >> >> >> Bob >> >> >> >> >> >> >> >> >> -----Original Message----- >> >> >> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx] >> >> >> Sent: 2016年4月11日 22:24 >> >> >> To: Wu, Bob >> >> >> Cc: xen-devel@xxxxxxxxxxxxx >> >> >> Subject: Re: [Xen-devel] Question about the XEN platform pci >> >> >> >> >> >> On Fri, Apr 08, 2016 at 08:52:08AM +0000, Wu, Bob wrote: >> >> >> > >> >> >> > Sorry bother, I read the XEN source code recently, and found the XEN >> >> >> > platform PCI code under drivers/xen/platform-pci.c, and I can't >> >> >> > fully under this driver's affect, can anybody explain a little for >> >> >> > me? >> >> >> > >> >> >> > Is the platform PCI driver for PV-split-PCI-driver-model such as the >> >> >> > pci-frontend/pci-backend? or for PCI pass-through model? Or for >> >> >> > other purpose? >> >> >> > I saw the xenbus_pcifront_driver/ xenbus_xen_pcibk_driver are >> >> >> > registered on XENBUS, so I guess the platform-PCI-driver is not for >> >> >> > PV PCI driver. >> >> >> > >> >> >> >> >> >> It is for the QEMU driver. To tell QEMU to stop emulating the >> >> >> IDE/network. >> >> >> >> >> >> > Really thank you for your replay. >> >> >> > >> >> >> > Thanks, >> >> >> > Bob >> >> >> > >> >> >> >> >> >> > _______________________________________________ >> >> >> > Xen-devel mailing list >> >> >> > Xen-devel@xxxxxxxxxxxxx >> >> >> > http://lists.xen.org/xen-devel >> >> >> >> >> > >> >> > _______________________________________________ >> >> > Xen-devel mailing list >> >> > Xen-devel@xxxxxxxxxxxxx >> >> > http://lists.xen.org/xen-devel >> >> >> >> >> >> >> >> -- >> >> Karim Allah Ahmed. >> >> >> >> -- >> Karim Allah Ahmed. -- Karim Allah Ahmed. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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