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

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Date:   Wed, 17 Mar 2021 11:12:44 -0700
From:   Nadav Amit <nadav.amit@...il.com>
To:     "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@...wei.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        chenjiashang <chenjiashang@...wei.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "Gonglei (Arei)" <arei.gonglei@...wei.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: A problem of Intel IOMMU hardware ？



> On Mar 17, 2021, at 2:35 AM, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) <longpeng2@...wei.com> wrote:
> 
> Hi Nadav,
> 
>> -----Original Message-----
>> From: Nadav Amit [mailto:nadav.amit@...il.com]
>>>  reproduce the problem with high probability (~50%).
>> 
>> I saw Lu replied, and he is much more knowledgable than I am (I was just intrigued
>> by your email).
>> 
>> However, if I were you I would try also to remove some “optimizations” to look for
>> the root-cause (e.g., use domain specific invalidations instead of page-specific).
>> 
> 
> Good suggestion! But we did it these days, we tried to use global invalidations as follow:
> 		iommu->flush.flush_iotlb(iommu, did, 0, 0,
> 						DMA_TLB_DSI_FLUSH);
> But can not resolve the problem.
> 
>> The first thing that comes to my mind is the invalidation hint (ih) in
>> iommu_flush_iotlb_psi(). I would remove it to see whether you get the failure
>> without it.
> 
> We also notice the IH, but the IH is always ZERO in our case, as the spec says:
> '''
> Paging-structure-cache entries caching second-level mappings associated with the specified
> domain-id and the second-level-input-address range are invalidated, if the Invalidation Hint
> (IH) field is Clear.
> '''
> 
> It seems the software is everything fine, so we've no choice but to suspect the hardware.

Ok, I am pretty much out of ideas. I have two more suggestions, but
they are much less likely to help. Yet, they can further help to rule
out software bugs:

1. dma_clear_pte() seems to be wrong IMHO. It should have used WRITE_ONCE()
to prevent split-write, which might potentially cause “invalid” (partially
cleared) PTE to be stored in the TLB. Having said that, the subsequent
IOTLB flush should have prevented the problem.

2. Consider ensuring that the problem is not somehow related to queued
invalidations. Try to use __iommu_flush_iotlb() instead of
qi_flush_iotlb().

Regards,
Nadav

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