linux-kernel - Re: [PATCH] iommu: intel: remove flooding of non-error logs, when new-DMA-PTE is the same as old-DMA-PTE.

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Date:   Mon, 11 Oct 2021 23:43:29 +0530
From:   Ajay Garg <ajaygargnsit@...il.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH] iommu: intel: remove flooding of non-error logs, when
 new-DMA-PTE is the same as old-DMA-PTE.

Thanks Alex for your time.

I think I may have found the issue. Right now, when doing a
dma-unmapping, we do a "soft-unmapping" only, as the pte-values
themselves are not cleared in the unlinked pagetable-frame.

I have made the (simple) changes, and things are looking good as of
now (almost an hour now).
However, this time I will give it a day ;)

If there is not a single-flooding observed in the next 24 hours, I
would float the v2 patch for review.


Thanks again for your time and patience.


Thanks and Regards,
Ajay


>
> Even this QEMU explanation doesn't make a lot of sense, vfio tracks
> userspace mappings and will return an -EEXIST error for duplicate or
> overlapping IOVA entries.  We expect to have an entirely empty IOMMU
> domain when a device is assigned, but it seems the only way userspace
> can trigger duplicate PTEs would be if mappings already exist, or we
> have a bug somewhere.
>
> If the most recent instance is purely on bare metal, then it seems the
> host itself has conflicting mappings.  I can only speculate with the
> limited data presented, but I'm suspicious there's something happening
> with RMRRs here (but that should also entirely preclude assignment).
> dmesg, lspci -vvv, and VM configuration would be useful.  Thanks,
>
> Alex
>