linux-kernel - RE: A problem of Intel IOMMU hardware ？

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Date:   Thu, 18 Mar 2021 08:56:10 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@...wei.com>, Nadav Amit <nadav.amit@...il.com>
CC:     chenjiashang <chenjiashang@...wei.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "Gonglei (Arei)" <arei.gonglei@...wei.com>,
        "will@...nel.org" <will@...nel.org>
Subject: RE: A problem of Intel IOMMU hardware ？

> From: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> <longpeng2@...wei.com>
> 
> > -----Original Message-----
> > From: Tian, Kevin [mailto:kevin.tian@...el.com]
> > Sent: Thursday, March 18, 2021 4:27 PM
> > To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> > <longpeng2@...wei.com>; Nadav Amit <nadav.amit@...il.com>
> > Cc: chenjiashang <chenjiashang@...wei.com>; David Woodhouse
> > <dwmw2@...radead.org>; iommu@...ts.linux-foundation.org; LKML
> > <linux-kernel@...r.kernel.org>; alex.williamson@...hat.com; Gonglei
> (Arei)
> > <arei.gonglei@...wei.com>; will@...nel.org
> > Subject: RE: A problem of Intel IOMMU hardware ？
> >
> > > From: iommu <iommu-bounces@...ts.linux-foundation.org> 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. 

Thanks
Kevin