linux-kernel - Re: [rfc v2 4/6] dma-direct: atomic allocations must come from atomic coherent pools

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Date:   Thu, 9 Apr 2020 16:24:41 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     David Rientjes <rientjes@...gle.com>,
        Christoph Hellwig <hch@....de>
Cc:     "Singh, Brijesh" <brijesh.singh@....com>,
        "Grimm, Jon" <jon.grimm@....com>, Joerg Roedel <joro@...tes.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: Re: [rfc v2 4/6] dma-direct: atomic allocations must come from atomic
 coherent pools

On 4/8/20 4:21 PM, David Rientjes wrote:
> When a device required unencrypted memory and the context does not allow

required => requires

> blocking, memory must be returned from the atomic coherent pools.
> 
> This avoids the remap when CONFIG_DMA_DIRECT_REMAP is not enabled and the
> config only requires CONFIG_DMA_COHERENT_POOL.  This will be used for
> CONFIG_AMD_MEM_ENCRYPT in a subsequent patch.
> 
> Keep all memory in these pools unencrypted.
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>   kernel/dma/direct.c | 16 ++++++++++++++++
>   kernel/dma/pool.c   | 15 +++++++++++++--
>   2 files changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 70800ca64f13..44165263c185 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -124,6 +124,18 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
>   	struct page *page;
>   	void *ret;
>   
> +	/*
> +	 * Unencrypted memory must come directly from DMA atomic pools if
> +	 * blocking is not allowed.
> +	 */
> +	if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
> +	    force_dma_unencrypted(dev) && !gfpflags_allow_blocking(gfp)) {
> +		ret = dma_alloc_from_pool(dev, PAGE_ALIGN(size), &page, gfp);
> +		if (!ret)
> +			return NULL;
> +		goto done;
> +	}
> +
>   	if (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
>   	    dma_alloc_need_uncached(dev, attrs) &&
>   	    !gfpflags_allow_blocking(gfp)) {
> @@ -203,6 +215,10 @@ void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
>   {
>   	unsigned int page_order = get_order(size);
>   
> +	if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
> +	    dma_free_from_pool(dev, cpu_addr, PAGE_ALIGN(size)))
> +		return;
> +
>   	if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
>   	    !force_dma_unencrypted(dev)) {
>   		/* cpu_addr is a struct page cookie, not a kernel address */
> diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> index e14c5a2da734..6685ab89cfa7 100644
> --- a/kernel/dma/pool.c
> +++ b/kernel/dma/pool.c
> @@ -9,6 +9,7 @@
>   #include <linux/dma-contiguous.h>
>   #include <linux/init.h>
>   #include <linux/genalloc.h>
> +#include <linux/set_memory.h>
>   #include <linux/slab.h>
>   #include <linux/vmalloc.h>
>   #include <linux/workqueue.h>
> @@ -55,12 +56,20 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
>   
>   	arch_dma_prep_coherent(page, pool_size);
>   
> +#ifdef CONFIG_DMA_DIRECT_REMAP
>   	addr = dma_common_contiguous_remap(page, pool_size,
>   					   pgprot_dmacoherent(PAGE_KERNEL),
>   					   __builtin_return_address(0));
>   	if (!addr)
>   		goto free_page;
> -
> +#else
> +	addr = page_to_virt(page);
> +#endif
> +	/*
> +	 * Memory in the atomic DMA pools must be unencrypted, the pools do not
> +	 * shrink so no re-encryption occurs in dma_direct_free_pages().
> +	 */
> +	set_memory_decrypted((unsigned long)page_to_virt(page), 1 << order);
>   	ret = gen_pool_add_virt(pool, (unsigned long)addr, page_to_phys(page),
>   				pool_size, NUMA_NO_NODE);
>   	if (ret)
> @@ -69,8 +78,10 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
>   	return 0;
>   
>   remove_mapping:
> +#ifdef CONFIG_DMA_DIRECT_REMAP
>   	dma_common_free_remap(addr, pool_size);

You're about to free the memory, but you've called set_memory_decrypted() 
against it, so you need to do a set_memory_encrypted() to bring it back to 
a state ready for allocation again.

Thanks,
Tom

> -free_page:
> +#endif
> +free_page: __maybe_unused
>   	if (!dma_release_from_contiguous(NULL, page, 1 << order))
>   		__free_pages(page, order);
>   out:
>