linux-kernel - Re: [PATCH v3 00/10] Update vfio_pin/unpin

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Date:   Fri, 22 Jul 2022 18:18:00 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     <kwankhede@...dia.com>, <corbet@....net>, <hca@...ux.ibm.com>,
        <gor@...ux.ibm.com>, <agordeev@...ux.ibm.com>,
        <borntraeger@...ux.ibm.com>, <svens@...ux.ibm.com>,
        <zhenyuw@...ux.intel.com>, <zhi.a.wang@...el.com>,
        <jani.nikula@...ux.intel.com>, <joonas.lahtinen@...ux.intel.com>,
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        <airlied@...ux.ie>, <daniel@...ll.ch>, <farman@...ux.ibm.com>,
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        <linux-s390@...r.kernel.org>,
        <intel-gvt-dev@...ts.freedesktop.org>,
        <intel-gfx@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <terrence.xu@...el.com>
Subject: Re: [PATCH v3 00/10] Update vfio_pin/unpin_pages API

On Fri, 22 Jul 2022 16:12:19 -0700
Nicolin Chen <nicolinc@...dia.com> wrote:

> On Fri, Jul 22, 2022 at 04:11:29PM -0600, Alex Williamson wrote:
> 
> > GVT-g explodes for me with this series on my Broadwell test system,
> > continuously spewing the following:  
> 
> Thank you for running additional tests.
> 
> > [   47.348778] WARNING: CPU: 3 PID: 501 at drivers/vfio/vfio_iommu_type1.c:978 vfio_iommu_type1_unpin_pages+0x7b/0x100 [vfio_iommu_type1]  
>  
> > Line 978 is the WARN_ON(i != npage) line.  For the cases where we don't
> > find a matching vfio_dma, I'm seeing addresses that look maybe like
> > we're shifting  a value that's already an iova by PAGE_SHIFT somewhere.  
> 
> Hmm..I don't understand the PAGE_SHIFT part. Do you mind clarifying?

The iova was a very large address for a 4GB VM with a lot of zeros on
the low order bits, ex. 0x162459000000.  Thanks,

Alex
 
> And GVT code initiated an unpin request from gvt_unpin_guest_pag()
> that is currently unpinning one page at a time on a contiguous IOVA
> range, prior to this series. After this series, it leaves the per-
> page routine to the internal loop of vfio_iommu_type1_unpin_pages(),
> which is supposed to do the same.
> 
> So, either resulted from the npage input being wrong or some other
> factor weighed in that invoked a vfio_remove_dma on those iovas?
> 
> Thanks
> Nic
>