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Date:   Tue, 31 Aug 2021 17:30:18 -0400
From:   Alyssa Rosenzweig <alyssa@rosenzweig.io>
To:     Sven Peter <sven@svenpeter.dev>
Cc:     iommu@lists.linux-foundation.org, Joerg Roedel <joro@8bytes.org>,
        Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Arnd Bergmann <arnd@kernel.org>,
        Mohamed Mediouni <mohamed.mediouni@caramail.com>,
        Alexander Graf <graf@amazon.com>,
        Hector Martin <marcan@marcan.st>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/8] iommu/dma: Disable get_sgtable for granule >
 PAGE_SIZE
Message-ID: <YS6fasuqPURbmC6X@sunset>
References: <20210828153642.19396-1-sven@svenpeter.dev>
 <20210828153642.19396-4-sven@svenpeter.dev>
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In-Reply-To: <20210828153642.19396-4-sven@svenpeter.dev>
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I use this function for cross-device sharing on the M1 display driver.
Arguably this is unsafe but it works on 16k kernels and if you want to
test the function on 4k, you know where my code is.

On Sat, Aug 28, 2021 at 05:36:37PM +0200, Sven Peter wrote:
> Pretend that iommu_dma_get_sgtable is not implemented when
> granule > PAGE_SIZE since I can neither test this function right now
> nor do I fully understand how it is used.
> 
> Signed-off-by: Sven Peter <sven@svenpeter.dev>
> ---
>  drivers/iommu/dma-iommu.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index d6e273ec3de6..64fbd9236820 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1315,9 +1315,15 @@ static int iommu_dma_get_sgtable(struct device *dev, struct sg_table *sgt,
>  		void *cpu_addr, dma_addr_t dma_addr, size_t size,
>  		unsigned long attrs)
>  {
> +	struct iommu_domain *domain = iommu_get_dma_domain(dev);
> +	struct iommu_dma_cookie *cookie = domain->iova_cookie;
> +	struct iova_domain *iovad = &cookie->iovad;
>  	struct page *page;
>  	int ret;
>  
> +	if (iovad->granule > PAGE_SIZE)
> +		return -ENXIO;
> +
>  	if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr)) {
>  		struct page **pages = dma_common_find_pages(cpu_addr);
>  
> -- 
> 2.25.1
>