linux-kernel - Re: [patch for-5.8 1/4] dma-direct: always align allocation size in dma_direct_alloc

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Date:   Mon, 15 Jun 2020 08:54:55 +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 1/4] dma-direct: always align allocation size
 in dma_direct_alloc_pages()

On Thu, Jun 11, 2020 at 12:20:28PM -0700, David Rientjes wrote:
> dma_alloc_contiguous() does size >> PAGE_SHIFT and set_memory_decrypted()
> works at page granularity.  It's necessary to page align the allocation
> size in dma_direct_alloc_pages() for consistent behavior.
> 
> This also fixes an issue when arch_dma_prep_coherent() is called on an
> unaligned allocation size for dma_alloc_need_uncached() when
> CONFIG_DMA_DIRECT_REMAP is disabled but CONFIG_ARCH_HAS_DMA_SET_UNCACHED
> is enabled.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  kernel/dma/direct.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -112,11 +112,12 @@ static inline bool dma_should_free_from_pool(struct device *dev,
>  struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
>  		gfp_t gfp, unsigned long attrs)
>  {
> -	size_t alloc_size = PAGE_ALIGN(size);
>  	int node = dev_to_node(dev);
>  	struct page *page = NULL;
>  	u64 phys_limit;
>  
> +	VM_BUG_ON(!PAGE_ALIGNED(size));

This really should be a WARN_ON_ONCE, but I've fixed this up before
applying.  I've also added a prep patch to mark __dma_direct_alloc_pages
static as part of auditing for other callers.