linux-kernel - Re: "dma-mapping: remove CONFIG_DMA

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Date:   Wed, 30 Mar 2022 10:55:27 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>
Cc:     Christoph Hellwig <hch@...radead.org>, regressions@...ts.linux.dev,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org
Subject: Re: "dma-mapping: remove CONFIG_DMA_REMAP" causes AMD SME boot fail

On Wed, Mar 30, 2022 at 01:51:07PM -0400, Alex Xu (Hello71) wrote:
> Hi,
> 
> After a recent kernel update, booting one of my machines causes it to 
> hang on a black screen. Pressing Lock keys on the USB keyboard does not 
> turn on the indicators, and the machine does not appear on the Ethernet 
> network. I don't have a serial port on this machine. I didn't try 
> netconsole, but I suspect it won't work.
> 
> Setting mem_encrypt=0 seems to resolve the issue. Reverting f5ff79fddf0e 
> ("dma-mapping: remove CONFIG_DMA_REMAP") also appears to resolve the 
> issue.
> 
> The machine in question has an AMD Ryzen 5 1600 and ASRock B450 Pro4.

This looks like something in the AMD IOMMU code or it's users can't
deal with vmalloc addresses.  I'll start looking for a culprit ASAP.