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

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Message-ID: <28161d94-6f2d-700f-853d-53b42f4d00d0@linux.intel.com>
Date:   Tue, 14 Jun 2022 15:21:23 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, 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()

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.

Best regards,
baolu