linux-kernel - Re: [patch for-5.8 4/4] dma-direct: add missing set_memory

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Date:   Mon, 15 Jun 2020 09:00:14 +0200
From:   Christoph Hellwig <hch@....de>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Christoph Hellwig <hch@....de>,
        Thomas Lendacky <thomas.lendacky@....com>,
        Brijesh Singh <brijesh.singh@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [patch for-5.8 4/4] dma-direct: add missing
 set_memory_decrypted() for coherent mapping

On Thu, Jun 11, 2020 at 12:20:32PM -0700, David Rientjes wrote:
> When a coherent mapping is created in dma_direct_alloc_pages(), it needs
> to be decrypted if the device requires unencrypted DMA before returning.
> 
> Fixes: 3acac065508f ("dma-mapping: merge the generic remapping helpers
> into dma-direct")
> Cc: stable@...r.kernel.org # 5.5+
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  kernel/dma/direct.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -195,6 +195,12 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
>  				__builtin_return_address(0));
>  		if (!ret)
>  			goto out_free_pages;
> +		if (force_dma_unencrypted(dev)) {
> +			err = set_memory_decrypted((unsigned long)ret,
> +						   1 << get_order(size));
> +			if (err)
> +				goto out_free_pages;
> +		}

Note that ret is a vmalloc address here.  Does set_memory_decrypted
work for that case?  Again this should be mostly theoretical, so I'm
not too worried for now.