Re: A problem of Intel IOMMU hardware ？

[Lu Baolu]

On 3/18/21 4:56 PM, Tian, Kevin wrote:
> > From: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> > <longpeng2@xxxxxxxxxx>
> >
> > > -----Original Message-----
> > > From: Tian, Kevin [mailto:kevin.tian@xxxxxxxxx]
> > > Sent: Thursday, March 18, 2021 4:27 PM
> > > To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> > > <longpeng2@xxxxxxxxxx>; Nadav Amit <nadav.amit@xxxxxxxxx>
> > > Cc: chenjiashang <chenjiashang@xxxxxxxxxx>; David Woodhouse
> > > <dwmw2@xxxxxxxxxxxxx>; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; LKML
> > > <linux-kernel@xxxxxxxxxxxxxxx>; alex.williamson@xxxxxxxxxx; Gonglei
> > (Arei)
> > > <arei.gonglei@xxxxxxxxxx>; will@xxxxxxxxxx
> > > Subject: RE: A problem of Intel IOMMU hardware ？
> > >
> > > > From: iommu <iommu-bounces@xxxxxxxxxxxxxxxxxxxxxxxxxx> On Behalf Of
> > > > Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> > > >
> > > > > 2. Consider ensuring that the problem is not somehow related to
> > > > > queued invalidations. Try to use __iommu_flush_iotlb() instead of
> > > qi_flush_iotlb().
> > > > >
> > > >
> > > > I tried to force to use __iommu_flush_iotlb(), but maybe something
> > > > wrong, the system crashed, so I prefer to lower the priority of this
> > operation.
> > > >
> > >
> > > The VT-d spec clearly says that register-based invalidation can be used only
> > when
> > > queued-invalidations are not enabled. Intel-IOMMU driver doesn't provide
> > an
> > > option to disable queued-invalidation though, when the hardware is
> > capable. If you
> > > really want to try, tweak the code in intel_iommu_init_qi.
> >
> > Hi Kevin,
> >
> > Thanks to point out this. Do you have any ideas about this problem ? I tried
> > to descript the problem much clear in my reply to Alex, hope you could have
> > a look if you're interested.
>
> btw I saw you used 4.18 kernel in this test. What about latest kernel?
>
> Also one way to separate sw/hw bug is to trace the low level interface (e.g.,
> qi_flush_iotlb) which actually sends invalidation descriptors to the IOMMU
> hardware. Check the window between b) and c) and see whether the
> software does the right thing as expected there.

Yes. It's better if we can reproduce this with the latest kernel which
has debugfs files to expose page tables and the invalidation queues etc.

Best regards,
baolu