linux-kernel - Re: [PATCH] iommu/amd: Fix unity mapping initialization race

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Message-ID: <CAKT61h9=yCdgsEXh3MQgtoyPb_Jzmpv2L_k-8gxHfqYwTYKKOw@mail.gmail.com>
Date:	Mon, 11 Jul 2016 18:05:51 +0800
From:	Wan ZongShun <mcuos.com@...il.com>
To:	Joerg Roedel <joro@...tes.org>
Cc:	Wan Zongshun <vw@...mu.org>, iommu@...ts.linux-foundation.org,
	Joerg Roedel <jroedel@...e.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	stable@...r.kernel.org
Subject: Re: [PATCH] iommu/amd: Fix unity mapping initialization race

>
>> Sorry, why you still say this 'init_device_table_dma' can block DMA?
>> I just think this function will enable DMA transfer, since  we set
>> the V and TV bits, right? or I misunderstand what "block DMA" mean?
>
> When the V and TV bits are not set, it means that all DMA from that
> device-id is forwared untranslated by the IOMMU. But if we set V and TV
> it means that there is translation information, and the IOMMU translates
> the requests using the rest of the DTE information. As all other bits
> are 0, this means that page-table-level is 0 (== no page-table) and that
> the global IW and IR bits are 0 too (== no read and write permissions).
> So all requests are blocked.
>

Clearly.

Thanks.

>
>
>         Joerg
>
> _______________________________________________
> iommu mailing list
> iommu@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu

-- 
---
Vincent Wan(Zongshun)
www.mcuos.com

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