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

Wan ZongShun
2016-07-11T10:06:19Z

>
>> 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
>
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Vincent Wan(Zongshun)