Messages in this thread Patch in this message | | | Date | Mon, 20 Sep 2021 16:16:06 -0700 (PDT) | From | Stefano Stabellini <> | Subject | Re: [PATCH] xen-pciback: allow compiling on other archs than x86 |
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On Mon, 20 Sep 2021, Oleksandr Andrushchenko wrote: > On 20.09.21 14:30, Juergen Gross wrote: > > On 20.09.21 07:23, Oleksandr Andrushchenko wrote: > >> Hello, Stefano! > >> > >> On 18.09.21 00:45, Stefano Stabellini wrote: > >>> Hi Oleksandr, > >>> > >>> Why do you want to enable pciback on ARM? Is it only to "disable" a PCI > >>> device in Dom0 so that it can be safely assigned to a DomU? > >> Not only that > >>> > >>> I am asking because actually I don't think we want to enable the PV PCI > >>> backend feature of pciback on ARM, right? That would clash with the PCI > >>> assignment work you have been doing in Xen. They couldn't both work at > >>> the same time. > >> Correct, it is not used > >>> > >>> If we only need pciback to "park" a device in Dom0, wouldn't it be > >>> possible and better to use pci-stub instead? > >> > >> Not only that, so pci-stub is not enough > >> > >> The functionality which is implemented by the pciback and the toolstack > >> and which is relevant/missing/needed for ARM: > >> > >> 1. pciback is used as a database for assignable PCI devices, e.g. xl > >> pci-assignable-{add|remove|list} manipulates that list. So, whenever the > >> toolstack needs to know which PCI devices can be passed through it reads > >> that from the relevant sysfs entries of the pciback. > >> > >> 2. pciback is used to hold the unbound PCI devices, e.g. when passing through > >> a PCI device it needs to be unbound from the relevant device driver and bound > >> to pciback (strictly speaking it is not required that the device is bound to > >> pciback, but pciback is again used as a database of the passed through PCI > >> devices, so we can re-bind the devices back to their original drivers when > >> guest domain shuts down) > >> > >> 3. Device reset > >> > >> We have previously discussed on xen-devel ML possible solutions to that as from the > >> above we see that pciback functionality is going to be only partially used on Arm. > >> > >> Please see [1] and [2]: > >> > >> 1. It is not acceptable to manage the assignable list in Xen itself > >> > >> 2. pciback can be split into two parts: PCI assignable/bind/reset handling and > >> the rest like vPCI etc. > >> > >> 3. pcifront is not used on Arm > > > > It is neither in x86 PVH/HVM guests. > Didn't know that, thank you for pointing > > > >> So, limited use of the pciback is one of the bricks used to enable PCI passthrough > >> on Arm. It was enough to just re-structure the driver and have it run on Arm to achieve > >> all the goals above. > >> > >> If we still think it is desirable to break the pciback driver into "common" and "pcifront specific" > >> parts then it can be done, yet the patch is going to be the very first brick in that building. > > > > Doing this split should be done, as the pcifront specific part could be > > omitted on x86, too, in case no PV guests using PCI passthrough have to > > be supported. > Agree, that the final solution should have the driver split > > > >> So, I think this patch is still going to be needed besides which direction we take. > > > > Some kind of this patch, yes. It might look different in case the split > > is done first. > > > > I don't mind doing it in either sequence. > > > With this patch we have Arm on the same page as the above mentioned x86 guests, > > e.g. the driver has unused code, but yet allows Arm to function now. > > At this stage of PCI passthrough on Arm it is yet enough. Long term, when > > the driver gets split, Arm will benefit from that split too, but unfortunately I do not > > have enough bandwidth for that piece of work at the moment.
That's fair and I don't want to scope-creep this simple patch asking for an enormous rework. At the same time I don't think we should enable the whole of pciback on ARM because it would be erroneous and confusing.
I am wonder if there is a simple:
if (!xen_pv_domain()) return;
That we could add in a couple of places in pciback to stop it from initializing the parts we don't care about. Something along these lines (untested and probably incomplete).
What do you guys think?
diff --git a/drivers/xen/xen-pciback/xenbus.c b/drivers/xen/xen-pciback/xenbus.c index da34ce85dc88..991ba0a9b359 100644 --- a/drivers/xen/xen-pciback/xenbus.c +++ b/drivers/xen/xen-pciback/xenbus.c @@ -15,6 +15,7 @@ #include <xen/xenbus.h> #include <xen/events.h> #include <xen/pci.h> +#include <xen/xen.h> #include "pciback.h" #define INVALID_EVTCHN_IRQ (-1) @@ -685,8 +686,12 @@ static int xen_pcibk_xenbus_probe(struct xenbus_device *dev, const struct xenbus_device_id *id) { int err = 0; - struct xen_pcibk_device *pdev = alloc_pdev(dev); + struct xen_pcibk_device *pdev; + + if (!xen_pv_domain()) + return 0; + pdev = alloc_pdev(dev); if (pdev == NULL) { err = -ENOMEM; xenbus_dev_fatal(dev, err, @@ -743,6 +748,9 @@ const struct xen_pcibk_backend *__read_mostly xen_pcibk_backend; int __init xen_pcibk_xenbus_register(void) { + if (!xen_pv_domain()) + return 0; + xen_pcibk_backend = &xen_pcibk_vpci_backend; if (passthrough) xen_pcibk_backend = &xen_pcibk_passthrough_backend; @@ -752,5 +760,7 @@ int __init xen_pcibk_xenbus_register(void) void __exit xen_pcibk_xenbus_unregister(void) { + if (!xen_pv_domain()) + return; xenbus_unregister_driver(&xen_pcibk_driver); } | |