On Thu, 2013-08-22 at 23:41 +0800, Wei Yang wrote:
> On Thu, Aug 22, 2013 at 09:28:23AM -0600, Alex Williamson wrote:
> >On Thu, 2013-08-22 at 15:52 +0800, Wei Yang wrote:
> >> On Thu, Aug 22, 2013 at 05:23:34PM +1000, Alexey Kardashevskiy wrote:
> >> >On 08/19/2013 11:55 AM, Wei Yang wrote:
> >> >> On Mon, Aug 19, 2013 at 11:39:49AM +1000, Alexey Kardashevskiy wrote:
> >> >>> On 08/19/2013 11:29 AM, Wei Yang wrote:
> >> >>>> On Fri, Aug 16, 2013 at 08:15:36PM +1000, Alexey Kardashevskiy wrote:
> >> >>>>> On 08/16/2013 08:08 PM, Wei Yang wrote:
> >> >>>>>> ---
> >> >>>>>> arch/powerpc/kernel/iommu.c | 3 ++-
> >> >>>>>> 1 files changed, 2 insertions(+), 1 deletions(-)
> >> >>>>>>
> >> >>>>>> diff --git a/arch/powerpc/kernel/iommu.c
> >> >>>>>> b/arch/powerpc/kernel/iommu.c
> >> >>>>>> index b20ff17..5abf7c3 100644
> >> >>>>>> --- a/arch/powerpc/kernel/iommu.c
> >> >>>>>> +++ b/arch/powerpc/kernel/iommu.c
> >> >>>>>> @@ -1149,7 +1149,8 @@ static int iommu_bus_notifier(struct
> >> >>>>>> notifier_block *nb,
> >> >>>>>> case BUS_NOTIFY_ADD_DEVICE:
> >> >>>>>> return iommu_add_device(dev);
> >> >>>>>> case BUS_NOTIFY_DEL_DEVICE:
> >> >>>>>> - iommu_del_device(dev);
> >> >>>>>> + if (dev->iommu_group)
> >> >>>>>> + iommu_del_device(dev);
> >> >>>>>> return 0;
> >> >>>>>> default:
> >> >>>>>> return 0;
> >> >>>>>>
> >> >>>>>
> >> >>>>> This one seems redundant, no?
> >> >>>>
> >> >>>> Sorry for the late.
> >> >>>>
> >> >>>> Yes, these two patches have the same purpose to guard the system,
> >> >>>> while in two
> >> >>>> different places. One is in powernv platform, the other is in the
> >> >>>> generic iommu
> >> >>>> driver.
> >> >>>>
> >> >>>> The one in powernv platform is used to correct the original logic.
> >> >>>>
> >> >>>> The one in generic iommu driver is to keep system safe in case other
> >> >>>> platform to
> >> >>>> call iommu_group_remove_device() without the check.
> >> >>>
> >> >>>
> >> >>> But I am moving bus notifier to powernv code (posted a patch last week,
> >> >>> otherwise Freescale's IOMMU conflicted) so this won't be the case.
> >> >>
> >> >> Yes, I see the patch.
> >> >>
> >> >> This means other platforms, besides powernv, will check the
> >> >> dev->iommu_group
> >> >> before remove the device? This would be a convention?
> >> >>
> >> >> If this is the case, the second patch is enough. We don't need to check
> >> >> it in
> >> >> generic iommu driver.
> >> >>
> >> >> Since I am not very familiar with the code convention, I post these two
> >> >> patches together. This doesn't mean I need to push both of them. Your
> >> >> comments
> >> >> are welcome, lets me understand which one is more suitable in this case.
> >> >
> >> >
> >> >Ok. So. I included the check in the bus notifier which I moved to powernv
> >> >platform, I guess I'll repost the series soon.
> >>
> >> Thanks, this check will guard the powernv platform.
> >>
> >> >
> >> >Good luck with pushing the fix for drivers/iommu/iommu.c :)
> >> >
> >>
> >> Alex,
> >>
> >> Sorry for not including you in the very beginning, which may spend you more
> >> efforts to track previous mails in this thread.
> >>
> >> Do you think it is reasonable to check the dev->iommu_group in
> >> iommu_group_remove_device()? Or we can count on the bus notifier to check
> >> it?
> >>
> >> Welcome your suggestions~
> >
> >I don't really see the point of patch 1/2. iommu_group_remove_device()
> >is specifically to remove a device from an iommu_group, so why would you
> >call it on a device that's not part of an iommu_group. If you want to
> >avoid testing dev->iommu_group, then implement the .remove_device
> >callback rather than using the notifier. Thanks,
> >
>
> You mean the .remove_device like intel_iommu_remove_device()?
>
> Hmm... this function didn't check the dev->iommu_group and just call
> iommu_group_remove_device(). I see this guard is put in iommu_bus_notifier(),
> which will check dev->iommu_group before invoke .remove_device.
>
> Let me explain the case to triger the problem a little.
>
> On some platform, like powernv, we implement another bus notifier when devices
> are added or removed in the system. Like Alexey mentioned, he missed the check
> for dev->iommu_group in the notifier before removing it from iommu_group. This
> trigger the crash.
>
> So do you think it is reasonable to guard the kernel in
> iommu_group_remove_device(), or we give the platform developers the
> responsibility to check the dev->iommu_group before calling it?
I don't see it as we need either patch 1/2 or patch 2/2. We absolutely
need some form of patch 2/2. Patch 1/2 isn't necessarily bad, but it
facilitates sloppy usage. The iommu driver shouldn't be calling
iommu_group_remove_device() on arbitrary devices that may or may not be
part of an iommu_group. Perhaps patch 1/2 should be:
if (WARN_ON(!group))
return;
Thanks,
Alex
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