lkml.org 
[lkml]   [2020]   [Jul]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] USB:Fix kernel NULL pointer when unbind UHCI form vfio-pci
On Fri, 24 Jul 2020 12:57:49 +0000
WeitaoWang-oc <WeitaoWang-oc@zhaoxin.com> wrote:

> On Thu, 23 Jul 2020 12:38:21 -0400, Alan wrote:
> > On Thu, Jul 23, 2020 at 10:17:35AM -0600, Alex Williamson wrote:
> > > The IOMMU grouping restriction does solve the hardware issue, so long
> > > as one driver doesn't blindly assume the driver private data for
> > > another device and modify it.
> >
> > Correction: The IOMMU grouping restriction solves the hardware issue for
> > vfio-pci. It won't necessarily help if some other driver comes along
> > and wants to bind to this hardware.
> >
> > > I do agree that your solution would
> > > work, requiring all devices are unbound before any can be bound, but it
> > > also seems difficult to manage. The issue is largely unique to USB
> > > AFAIK. On the other hand, drivers coordinating with each other to
> > > register their _private_ data as share-able within a set of drivers
> > > seems like a much more direct and explicit interaction between the
> > > drivers. Thanks,
> >
> > Yes, that makes sense. But it would have to be implemented in the
> > driver core, not in particular subsystems like USB or PCI. And it might
> > be seen as overkill, given that only UHCI/OHCI/EHCI devices require this
> > sort of sharing AFAIK.
> >
> > Also, when you think about it, what form would such coordination among
> > drivers take? From your description, it sounds like the drivers would
> > agree to avoid accessing each other's private data if the proper
> > registration wasn't in place.
> >
> > On the other hand, a stronger and perhaps more robust approach would be
> > to enforce the condition that non-cooperating drivers are never bound to
> > devices in the same group at the same time. That's basically what I'm
> > proposing here -- the question is whether the enforcement should be
> > instituted in the kernel or should merely be part of a standard protocol
> > followed by userspace drivers.
> >
> > Given that it's currently needed in only one place, it seems reasonable
> > to leave this as a "gentlemen's agreement" in userspace for the time
> > being instead of adding it to the kernel.
> >
>
> Provided that EHCI and UHCI host controller declare not support P2P and
> ACS. So, we can assign EHCI and UHCI host controller to different IOMMU
> group separately. We assign EHCI host controller to host and assign UHCI
> host controller to VM. Then, ehci_hcd driver load/unload operation in host
> will cause the same issue as discussed

And you have an example of such a device? I expect these do not exist,
nor should they. It seems like it would be an improper use of ACS.
Thanks,

Alex

\
 
 \ /
  Last update: 2020-07-24 21:18    [W:0.076 / U:0.420 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site