linux-kernel - RE: [PATCH v2 03/12] iommu/vt-d: Remove clearing translation data in disable_dmar

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Date:   Wed, 15 Jun 2022 06:22:47 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Jason Gunthorpe" <jgg@...dia.com>
CC:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 03/12] iommu/vt-d: Remove clearing translation data in
 disable_dmar_iommu()

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Tuesday, June 14, 2022 3:21 PM
> 
> On 2022/6/14 14:49, Tian, Kevin wrote:
> >> From: Lu Baolu<baolu.lu@...ux.intel.com>
> >> Sent: Tuesday, June 14, 2022 10:51 AM
> >>
> >> The disable_dmar_iommu() is called when IOMMU initialization fails or
> >> the IOMMU is hot-removed from the system. In both cases, there is no
> >> need to clear the IOMMU translation data structures for devices.
> >>
> >> On the initialization path, the device probing only happens after the
> >> IOMMU is initialized successfully, hence there're no translation data
> >> structures.
> > Out of curiosity. With kexec the IOMMU may contain stale mappings
> > from the old kernel. Then is it meaningful to disable IOMMU after the
> > new kernel fails to initialize it properly?
> 
> For kexec kernel, if the IOMMU is detected to be pre-enabled, the IOMMU
> driver will try to copy tables from the old kernel. If copying table
> fails, the IOMMU driver will disable IOMMU and do the normal
> initialization.
>

What about an error occurred after copying table in the initialization
path? The new kernel will be in a state assuming iommu is disabled
but it is still enabled using an old mapping for certain devices...