Re: [PATCH v3 2/9] dma-direct: use DMA_ATTR_CC_SHARED in alloc/free paths

[Aneesh Kumar K . V]

Catalin Marinas <catalin.marinas@xxxxxxx> writes:

> On Mon, Apr 27, 2026 at 11:25:02AM +0530, Aneesh Kumar K.V (Arm) wrote:
>> @@ -365,10 +389,14 @@ void dma_direct_free(struct device *dev, size_t size,
>>  struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
>>  		dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp)
>>  {
>> +	unsigned long attrs = 0;
>>  	struct page *page;
>>  	void *ret;
>>  
>> -	if (force_dma_unencrypted(dev) && dma_direct_use_pool(dev, gfp))
>> +	if (force_dma_unencrypted(dev))
>> +		attrs |= DMA_ATTR_CC_SHARED;
>> +
>> +	if ((attrs & DMA_ATTR_CC_SHARED) && dma_direct_use_pool(dev, gfp))
>>  		return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
>
> I was looking at Sashiko's reports and it noticed the wrong type
> returned here. Not something your patch introduces but I think it should
> be fixed rather than continue to propagate it. It's been around since
> 5.10, commit 5b138c534fda ("dma-direct: factor out a
> dma_direct_alloc_from_pool helper"). This code path isn't used much I
> guess.
>

I can add this change as one of the patch

modified    kernel/dma/direct.c
@@ -165,24 +165,24 @@
 	return !gfpflags_allow_blocking(gfp) && !is_swiotlb_for_alloc(dev);
 }
 
-static void *dma_direct_alloc_from_pool(struct device *dev, size_t size,
-		dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
+static struct page *dma_direct_alloc_from_pool(struct device *dev, size_t size,
+		dma_addr_t *dma_handle, void **cpu_addr, gfp_t gfp,
+		unsigned long attrs)
 {
 	struct page *page;
 	u64 phys_limit;
-	void *ret;
 
 	if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_DMA_COHERENT_POOL)))
 		return NULL;
 
 	gfp |= dma_direct_optimal_gfp_mask(dev, &phys_limit);
-	page = dma_alloc_from_pool(dev, size, &ret, gfp, attrs,
-				  dma_coherent_ok);
+	page = dma_alloc_from_pool(dev, size, cpu_addr, gfp, attrs,
+				   dma_coherent_ok);
 	if (!page)
 		return NULL;
 	*dma_handle = phys_to_dma_direct(dev, page_to_phys(page),
 					 !!(attrs & DMA_ATTR_CC_SHARED));
-	return ret;
+	return page;
 }
 
 static void *dma_direct_alloc_no_mapping(struct device *dev, size_t size,
@@ -212,7 +212,7 @@
 	bool mark_mem_decrypt = false;
 	bool allow_highmem = true;
 	struct page *page;
-	void *ret;
+	void *cpu_addr;
 
 	/*
 	 * DMA_ATTR_CC_SHARED is not a caller-visible dma_alloc_*()
@@ -278,9 +278,12 @@
 	 * the atomic pools instead if we aren't allowed block.
 	 */
 	if ((remap || (attrs & DMA_ATTR_CC_SHARED)) &&
-	    dma_direct_use_pool(dev, gfp))
-		return dma_direct_alloc_from_pool(dev, size, dma_handle,
-					  gfp, attrs);
+	    dma_direct_use_pool(dev, gfp)) {
+		page = dma_direct_alloc_from_pool(dev, size,
+					dma_handle, &cpu_addr,
+					gfp, attrs);
+		return page ? cpu_addr : NULL;
+	}
 
 	if (is_swiotlb_for_alloc(dev)) {
 		page = dma_direct_alloc_swiotlb(dev, size, attrs);
@@ -318,12 +321,12 @@
 		arch_dma_prep_coherent(page, size);
 
 		/* create a coherent mapping */
-		ret = dma_common_contiguous_remap(page, size, prot,
+		cpu_addr = dma_common_contiguous_remap(page, size, prot,
 				__builtin_return_address(0));
-		if (!ret)
+		if (!cpu_addr)
 			goto out_free_pages;
 	} else {
-		ret = page_address(page);
+		cpu_addr = page_address(page);
 	}
 
 	if (mark_mem_decrypt) {
@@ -334,18 +337,18 @@
 			goto out_leak_pages;
 	}
 
-	memset(ret, 0, size);
+	memset(cpu_addr, 0, size);
 
 	if (set_uncached) {
 		arch_dma_prep_coherent(page, size);
-		ret = arch_dma_set_uncached(ret, size);
-		if (IS_ERR(ret))
+		cpu_addr = arch_dma_set_uncached(cpu_addr, size);
+		if (IS_ERR(cpu_addr))
 			goto out_encrypt_pages;
 	}
 
 	*dma_handle = phys_to_dma_direct(dev, page_to_phys(page),
 					 !!(attrs & DMA_ATTR_CC_SHARED));
-	return ret;
+	return cpu_addr;
 
 out_encrypt_pages:
 	if (mark_mem_decrypt && dma_set_encrypted(dev, page_address(page), size))
@@ -427,14 +430,14 @@
 {
 	unsigned long attrs = 0;
 	struct page *page;
-	void *ret;
+	void *cpu_addr;
 
 	if (force_dma_unencrypted(dev))
 		attrs |= DMA_ATTR_CC_SHARED;
 
 	if ((attrs & DMA_ATTR_CC_SHARED) && dma_direct_use_pool(dev, gfp))
 		return dma_direct_alloc_from_pool(dev, size, dma_handle,
-					  gfp, attrs);
+					&cpu_addr, gfp, attrs);
 
 	if (is_swiotlb_for_alloc(dev)) {
 		page = dma_direct_alloc_swiotlb(dev, size, attrs);
@@ -445,7 +448,7 @@
 			swiotlb_free(dev, page, size);
 			return NULL;
 		}
-		ret = page_address(page);
+		cpu_addr = page_address(page);
 		goto setup_page;
 	}
 
@@ -453,11 +456,11 @@
 	if (!page)
 		return NULL;
 
-	ret = page_address(page);
-	if ((attrs & DMA_ATTR_CC_SHARED) && dma_set_decrypted(dev, ret, size))
+	cpu_addr = page_address(page);
+	if ((attrs & DMA_ATTR_CC_SHARED) && dma_set_decrypted(dev, cpu_addr, size))
 		goto out_leak_pages;
 setup_page:
-	memset(ret, 0, size);
+	memset(cpu_addr, 0, size);
 	*dma_handle = phys_to_dma_direct(dev, page_to_phys(page),
 					 !!(attrs & DMA_ATTR_CC_SHARED));
 	return page;