Re: [PATCH 03/11] dma-direct: always leak memory that can't be re-encrypted

[Robin Murphy <robin.murphy@arm.com>]

On 2021-11-11 06:50, Christoph Hellwig wrote:
> We must never unencryped memory go back into the general page pool.
> So if we fail to set it back to encrypted when freeing DMA memory, leak
> the memory insted and warn the user.

Nit: typos of "unencrypted" and "instead". Plus presumably the first 
sentence was meant to have a "let" or similar in there too.

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   kernel/dma/direct.c | 14 ++++++++++----
>   1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 996ba4edb2fa3..d7a489be48470 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -84,9 +84,14 @@ static int dma_set_decrypted(struct device *dev, void *vaddr, size_t size)
>   
>   static int dma_set_encrypted(struct device *dev, void *vaddr, size_t size)
>   {
> +	int ret;
> +
>   	if (!force_dma_unencrypted(dev))
>   		return 0;
> -	return set_memory_encrypted((unsigned long)vaddr, 1 << get_order(size));
> +	ret = set_memory_encrypted((unsigned long)vaddr, 1 << get_order(size));
> +	if (ret)
> +		pr_warn_ratelimited("leaking DMA memory that can't be re-encrypted\n");
> +	return ret;
>   }
>   
>   static void __dma_direct_free_pages(struct device *dev, struct page *page,
> @@ -261,7 +266,6 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>   	return ret;
>   
>   out_encrypt_pages:
> -	/* If memory cannot be re-encrypted, it must be leaked */
>   	if (dma_set_encrypted(dev, page_address(page), size))
>   		return NULL;
>   out_free_pages:
> @@ -307,7 +311,8 @@ void dma_direct_free(struct device *dev, size_t size,
>   	} else {
>   		if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
>   			arch_dma_clear_uncached(cpu_addr, size);
> -		dma_set_encrypted(dev, cpu_addr, 1 << page_order);
> +		if (dma_set_encrypted(dev, cpu_addr, 1 << page_order))
> +			return;
>   	}
>   
>   	__dma_direct_free_pages(dev, dma_direct_to_page(dev, dma_addr), size);
> @@ -361,7 +366,8 @@ void dma_direct_free_pages(struct device *dev, size_t size,
>   	    dma_free_from_pool(dev, vaddr, size))
>   		return;
>   
> -	dma_set_encrypted(dev, vaddr, 1 << page_order);
> +	if (dma_set_encrypted(dev, vaddr, 1 << page_order))
> +		return;
>   	__dma_direct_free_pages(dev, page, size);
>   }
>   
> 
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