linux-kernel - Re: [PATCH] iommu/amd: Mark translation invalid during device detach

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Date:   Wed, 16 Jan 2019 14:35:51 +0000
From:   "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
To:     "joro@...tes.org" <joro@...tes.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "Singh, Brijesh" <brijesh.singh@....com>
Subject: Re: [PATCH] iommu/amd: Mark translation invalid during device detach

Joerg,

On 1/16/19 8:03 PM, joro@...tes.org wrote:
> Hi Suravee,
> 
> On Wed, Jan 16, 2019 at 04:15:10AM +0000, Suthikulpanit, Suravee wrote:
>> From: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
>>
>> When a device switches domain, IOMMU driver detach device from the old
>> domain, and attach device to the new domain. During this period
>> the host table root pointer is not set, which means DMA translation
>> should be marked as invalid (clear TV bit).
>>
>> So, clear the TV bit when detach the device. The TV bit will be set
>> again when attaching device to the new domain.
> 
> Is there a specific problem with setting the TV bit?

We are not currently seeing issue.

> Note that the update will clear all other fields in the first 128 bits
> of the DTE, which means that IR, IW and Mode are all set to 0. This
> effectivly blocks all DMA requests from the device, which is by design.

Ahh.. This makes sense now. I missed the IR/IW/Mode=0 part.
It was not clear to us earlier. Thanks for clarification.

Regards,
Suravee