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

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Message-ID: <YkUpSy4snmZ7E5xX@infradead.org>
Date:   Wed, 30 Mar 2022 21:08:43 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>
Cc:     Christoph Hellwig <hch@...radead.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        regressions@...ts.linux.dev
Subject: Re: "dma-mapping: remove CONFIG_DMA_REMAP" causes AMD SME boot fail

On Wed, Mar 30, 2022 at 03:17:20PM -0400, Alex Xu (Hello71) wrote:
> Excerpts from Christoph Hellwig's message of March 30, 2022 2:01 pm:
> > Can you try this patch, which is a bit of a hack?
> > 
> > diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> > index 50d209939c66c..61997c2ee0a17 100644
> > --- a/arch/x86/mm/mem_encrypt.c
> > +++ b/arch/x86/mm/mem_encrypt.c
> > @@ -28,7 +28,8 @@ bool force_dma_unencrypted(struct device *dev)
> >  	 * device does not support DMA to addresses that include the
> >  	 * encryption mask.
> >  	 */
> > -	if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT)) {
> > +	if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT) &&
> > +	    !get_dma_ops(dev)) {
> >  		u64 dma_enc_mask = DMA_BIT_MASK(__ffs64(sme_me_mask));
> >  		u64 dma_dev_mask = min_not_zero(dev->coherent_dma_mask,
> >  						dev->bus_dma_limit);
> > 
> 
> This seems to work for me.

Ok, I'll try to come up with a less hacky version and will start a
discussion with the AMD folks that know memory encryption better.
Thanks for the report and testing already!