Re: [PATCH 2/2] arm/dma-mapping: Respect NO_KERNEL_MAPPING when we don't have an IOMMU

[Laura Abbott <lauraa@codeaurora.org>]

On 2/3/2015 12:47 AM, Carlo Caione wrote:
> From: "Jasper St. Pierre" <jstpierre@mecheye.net>
>
> Even without an iommu, NO_KERNEL_MAPPING is still convenient to save on
> kernel address space in places where we don't need a kernel mapping.
> Implement support for it in the two places where we're creating an
> expensive mapping.
>
> __alloc_from_pool uses an internal pool from which we already have
> virtual addresses, so it's not relevant, and __alloc_simple_buffer
> uses alloc_pages, which will always return a lowmem page, which is
> already mapped into kernel space, so we can't prevent a mapping for it
> in that case.
>
> Signed-off-by: Jasper St. Pierre <jstpierre@mecheye.net>
> Signed-off-by: Carlo Caione <carlo@caione.org>
> Reviewed-by: Rob Clark <robdclark@gmail.com>
> Reviewed-by: Daniel Drake <dsd@endlessm.com>
> ---
>   arch/arm/mm/dma-mapping.c | 67 +++++++++++++++++++++++++++++------------------
>   1 file changed, 41 insertions(+), 26 deletions(-)
>
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index a673c7f..6843293 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -289,11 +289,11 @@ static void __dma_free_buffer(struct page *page, size_t size)
>
>   static void *__alloc_from_contiguous(struct device *dev, size_t size,
>   				     pgprot_t prot, struct page **ret_page,
> -				     const void *caller);
> +				     const void *caller, bool want_vaddr);
>
>   static void *__alloc_remap_buffer(struct device *dev, size_t size, gfp_t gfp,
>   				 pgprot_t prot, struct page **ret_page,
> -				 const void *caller);
> +				 const void *caller, bool want_vaddr);
>
>   static void *
>   __dma_alloc_remap(struct page *page, size_t size, gfp_t gfp, pgprot_t prot,
> @@ -357,10 +357,10 @@ static int __init atomic_pool_init(void)
>
>   	if (dev_get_cma_area(NULL))
>   		ptr = __alloc_from_contiguous(NULL, atomic_pool_size, prot,
> -					      &page, atomic_pool_init);
> +					      &page, atomic_pool_init, true);
>   	else
>   		ptr = __alloc_remap_buffer(NULL, atomic_pool_size, gfp, prot,
> -					   &page, atomic_pool_init);
> +					   &page, atomic_pool_init, true);
>   	if (ptr) {
>   		int ret;
>
> @@ -467,13 +467,15 @@ static void __dma_remap(struct page *page, size_t size, pgprot_t prot)
>
>   static void *__alloc_remap_buffer(struct device *dev, size_t size, gfp_t gfp,
>   				 pgprot_t prot, struct page **ret_page,
> -				 const void *caller)
> +				 const void *caller, bool want_vaddr)
>   {
>   	struct page *page;
> -	void *ptr;
> +	void *ptr = NULL;
>   	page = __dma_alloc_buffer(dev, size, gfp);
>   	if (!page)
>   		return NULL;
> +	if (!want_vaddr)
> +		goto out;
>
>   	ptr = __dma_alloc_remap(page, size, gfp, prot, caller);
>   	if (!ptr) {
> @@ -481,6 +483,7 @@ static void *__alloc_remap_buffer(struct device *dev, size_t size, gfp_t gfp,
>   		return NULL;
>   	}
>
> + out:
>   	*ret_page = page;
>   	return ptr;
>   }
> @@ -523,12 +526,12 @@ static int __free_from_pool(void *start, size_t size)
>
>   static void *__alloc_from_contiguous(struct device *dev, size_t size,
>   				     pgprot_t prot, struct page **ret_page,
> -				     const void *caller)
> +				     const void *caller, bool want_vaddr)
>   {
>   	unsigned long order = get_order(size);
>   	size_t count = size >> PAGE_SHIFT;
>   	struct page *page;
> -	void *ptr;
> +	void *ptr = NULL;
>
>   	page = dma_alloc_from_contiguous(dev, count, order);
>   	if (!page)
> @@ -536,6 +539,9 @@ static void *__alloc_from_contiguous(struct device *dev, size_t size,
>
>   	__dma_clear_buffer(page, size);
>
> +	if (!want_vaddr)
> +		goto out;
> +
>   	if (PageHighMem(page)) {
>   		ptr = __dma_alloc_remap(page, size, GFP_KERNEL, prot, caller);
>   		if (!ptr) {
> @@ -546,17 +552,21 @@ static void *__alloc_from_contiguous(struct device *dev, size_t size,
>   		__dma_remap(page, size, prot);
>   		ptr = page_address(page);
>   	}
> +
> + out:
>   	*ret_page = page;
>   	return ptr;
>   }
>
>   static void __free_from_contiguous(struct device *dev, struct page *page,
> -				   void *cpu_addr, size_t size)
> +				   void *cpu_addr, size_t size, bool want_vaddr)
>   {
> -	if (PageHighMem(page))
> -		__dma_free_remap(cpu_addr, size);
> -	else
> -		__dma_remap(page, size, PAGE_KERNEL);
> +	if (want_vaddr) {
> +		if (PageHighMem(page))
> +			__dma_free_remap(cpu_addr, size);
> +		else
> +			__dma_remap(page, size, PAGE_KERNEL);
> +	}
>   	dma_release_from_contiguous(dev, page, size >> PAGE_SHIFT);
>   }
>
> @@ -574,12 +584,12 @@ static inline pgprot_t __get_dma_pgprot(struct dma_attrs *attrs, pgprot_t prot)
>
>   #define nommu() 1
>
> -#define __get_dma_pgprot(attrs, prot)	__pgprot(0)
> -#define __alloc_remap_buffer(dev, size, gfp, prot, ret, c)	NULL
> +#define __get_dma_pgprot(attrs, prot)				__pgprot(0)
> +#define __alloc_remap_buffer(dev, size, gfp, prot, ret, c, wv)	NULL
>   #define __alloc_from_pool(size, ret_page)			NULL
> -#define __alloc_from_contiguous(dev, size, prot, ret, c)	NULL
> +#define __alloc_from_contiguous(dev, size, prot, ret, c, wv)	NULL
>   #define __free_from_pool(cpu_addr, size)			0
> -#define __free_from_contiguous(dev, page, cpu_addr, size)	do { } while (0)
> +#define __free_from_contiguous(dev, page, cpu_addr, size, wv)	do { } while (0)
>   #define __dma_free_remap(cpu_addr, size)			do { } while (0)
>
>   #endif	/* CONFIG_MMU */
> @@ -599,11 +609,13 @@ static void *__alloc_simple_buffer(struct device *dev, size_t size, gfp_t gfp,
>
>
>   static void *__dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
> -			 gfp_t gfp, pgprot_t prot, bool is_coherent, const void *caller)
> +			 gfp_t gfp, pgprot_t prot, bool is_coherent,
> +			 struct dma_attrs *attrs, const void *caller)
>   {
>   	u64 mask = get_coherent_dma_mask(dev);
>   	struct page *page = NULL;
>   	void *addr;
> +	bool want_vaddr;
>
>   #ifdef CONFIG_DMA_API_DEBUG
>   	u64 limit = (mask + 1) & ~mask;
> @@ -631,20 +643,21 @@ static void *__dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
>
>   	*handle = DMA_ERROR_CODE;
>   	size = PAGE_ALIGN(size);
> +	want_vaddr = !dma_get_attr(DMA_ATTR_NO_KERNEL_MAPPING, attrs);
>
>   	if (is_coherent || nommu())
>   		addr = __alloc_simple_buffer(dev, size, gfp, &page);
>   	else if (!(gfp & __GFP_WAIT))
>   		addr = __alloc_from_pool(size, &page);
>   	else if (!dev_get_cma_area(dev))
> -		addr = __alloc_remap_buffer(dev, size, gfp, prot, &page, caller);
> +		addr = __alloc_remap_buffer(dev, size, gfp, prot, &page, caller, want_vaddr);
>   	else
> -		addr = __alloc_from_contiguous(dev, size, prot, &page, caller);
> +		addr = __alloc_from_contiguous(dev, size, prot, &page, caller, want_vaddr);
>
> -	if (addr)
> +	if (page)
>   		*handle = pfn_to_dma(dev, page_to_pfn(page));
>
> -	return addr;
> +	return want_vaddr ? addr : &page;
>   }
>
  
What happens if __alloc_remap_buffer or __alloc_from_contiguous fails to allocate?
 From this, its seems like we will return &page which will always be non-null
so it will look like a success.

Thanks,
Laura

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