linux-kernel - Re: [PATCH v14 00/13] SMMUv3 Nested Stage Setup (IOMMU part)

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Message-ID: <467c95cd-3ba5-519e-cdac-9f477da86ecb@nvidia.com>
Date:   Fri, 23 Apr 2021 23:49:55 +0530
From:   Sumit Gupta <sumitg@...dia.com>
To:     Krishna Reddy <vdumpa@...dia.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
CC:     "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "eric.auger.pro@...il.com" <eric.auger.pro@...il.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "jiangkunkun@...wei.com" <jiangkunkun@...wei.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "lushenming@...wei.com" <lushenming@...wei.com>,
        "maz@...nel.org" <maz@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "tn@...ihalf.com" <tn@...ihalf.com>,
        "vivek.gautam@....com" <vivek.gautam@....com>,
        Vikram Sethi <vsethi@...dia.com>,
        "wangxingang5@...wei.com" <wangxingang5@...wei.com>,
        "will@...nel.org" <will@...nel.org>,
        "zhangfei.gao@...aro.org" <zhangfei.gao@...aro.org>,
        "zhukeqian1@...wei.com" <zhukeqian1@...wei.com>,
        Sachin Nikam <Snikam@...dia.com>,
        Bibek Basu <bbasu@...dia.com>,
        Shanker Donthineni <sdonthineni@...dia.com>,
        Sumit Gupta <sumitg@...dia.com>
Subject: Re: [PATCH v14 00/13] SMMUv3 Nested Stage Setup (IOMMU part)



>>> Did that patch cause any issue, or is it just not needed on your system?
>>> It fixes an hypothetical problem with the way ATS is implemented.
>>> Maybe I actually observed it on an old software model, I don't
>>> remember. Either way it's unlikely to go upstream but I'd like to know
>>> if I should drop it from my tree.
> 
>> Had to revert same patch "mm: notify remote TLBs when dirtying a PTE" to
>> avoid below crash[1]. I am not sure about the cause yet.
> 
> I have noticed this issue earlier with patch pointed here and root caused the issue as below.
> It happens after vfio_mmap request from QEMU for the PCIe device and during the access of VA when
> PTE access flags are updated.
> 
> kvm_mmu_notifier_change_pte() --> kvm_set_spte_hve() --> kvm_set_spte_hva() --> clean_dcache_guest_page()
> 
> The validation model doesn't have FWB capability supported.
> __clean_dcache_guest_page() attempts to perform dcache flush on pcie bar address(not a valid_pfn()) through page_address(),
> which doesn't have page table mapping and leads to exception.
> 
> I have worked around the issue by filtering out the request if the pfn is not valid in  __clean_dcache_guest_page().
> As the patch wasn't posted in the community, reverted it as well.

Thank you Krishna for sharing the analysis.

Best Regards,
Sumit Gupta