linux-kernel - Re: [rfc 5/6] dma-direct: atomic allocations must come from unencrypted pools

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Date:   Thu, 5 Mar 2020 16:44:56 +0100
From:   Christoph Hellwig <hch@....de>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Christoph Hellwig <hch@....de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Singh, Brijesh" <brijesh.singh@....com>,
        "Grimm, Jon" <jon.grimm@....com>, Joerg Roedel <joro@...tes.org>,
        baekhw@...gle.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: Re: [rfc 5/6] dma-direct: atomic allocations must come from
 unencrypted pools

On Sun, Mar 01, 2020 at 04:05:23PM -0800, David Rientjes wrote:
> When AMD memory encryption is enabled, all non-blocking DMA allocations
> must originate from the atomic pools depending on the device and the gfp
> mask of the allocation.
> 
> Keep all memory in these pools unencrypted.
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  arch/x86/Kconfig    | 1 +
>  kernel/dma/direct.c | 9 ++++-----
>  kernel/dma/remap.c  | 2 ++
>  3 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1523,6 +1523,7 @@ config X86_CPA_STATISTICS
>  config AMD_MEM_ENCRYPT
>  	bool "AMD Secure Memory Encryption (SME) support"
>  	depends on X86_64 && CPU_SUP_AMD
> +	select DMA_DIRECT_REMAP

I think we need to split the pool from remapping so that we don't drag
in the remap code for x86.

>  	if (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
> -	    dma_alloc_need_uncached(dev, attrs) &&

We still need a check here for either uncached or memory encryption.

> @@ -141,6 +142,7 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
>  	if (!addr)
>  		goto free_page;
>  
> +	set_memory_decrypted((unsigned long)page_to_virt(page), nr_pages);

This probably warrants a comment.

Also I think the infrastructure changes should be split from the x86
wire up.