Re: [PATCH v8 01/23] dma-direct: return struct page from dma_direct_alloc_from_pool()

Leon Romanovsky [off-list ref] writes:

On Fri, Jul 17, 2026 at 11:34:19PM +0530, Aneesh Kumar K.V (Arm) wrote:

quoted

Commit 5b138c534fda ("dma-direct: factor out a dma_direct_alloc_from_pool
helper") changed dma_direct_alloc_from_pool() to return the CPU address
from dma_alloc_from_pool(). That fits dma_direct_alloc(), but
dma_direct_alloc_pages() also uses the helper and expects a struct page *.

Fix this by making dma_direct_alloc_from_pool() return the struct page *
again, and pass the CPU address back through an out-parameter for the
dma_direct_alloc() caller.

Fixes: 5b138c534fda ("dma-direct: factor out a dma_direct_alloc_from_pool helper")
Cc: stable@vger.kernel.org
Tested-by: Michael Kelley <redacted>
Tested-by: Mostafa Saleh <smostafa@google.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 kernel/dma/direct.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index d8219efe3273..363d984d90e7 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c

@@ -164,22 +164,21 @@ static bool dma_direct_use_pool(struct device *dev, gfp_t gfp)
 	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)
+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)
 {
 	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, dma_coherent_ok);
+	page = dma_alloc_from_pool(dev, size, cpu_addr, gfp, dma_coherent_ok);
 	if (!page)
 		return NULL;
 	*dma_handle = phys_to_dma_direct(dev, page_to_phys(page));
-	return ret;
+	return page;
 }
 
 static void *dma_direct_alloc_no_mapping(struct device *dev, size_t size,

@@ -247,8 +246,11 @@ void *dma_direct_alloc(struct device *dev, size_t size,
 	 * the atomic pools instead if we aren't allowed block.
 	 */
 	if ((remap || force_dma_unencrypted(dev)) &&
-	    dma_direct_use_pool(dev, gfp))
-		return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
+	    dma_direct_use_pool(dev, gfp)) {
+		page = dma_direct_alloc_from_pool(dev, size, dma_handle,
+						  &ret, gfp);
+		return page ? ret : NULL;

Sorry for joining the discussion late, but the line above caught my
attention.

Why do we need both ret and page? We can derive cpu_addr from page and
vice versa. Do we really need the &ret parameter? Or, more generally, do
we really need "struct page *"?

static struct page *__dma_alloc_from_pool(struct device *dev, size_t size,
		struct gen_pool *pool, void **cpu_addr,
		bool (*phys_addr_ok)(struct device *, phys_addr_t, size_t))
{
...
	*cpu_addr = (void *)addr;
	memset(*cpu_addr, 0, size);
	return pfn_to_page(__phys_to_pfn(phys));
}

Why

With CONFIG_DMA_DIRECT_REMAP the cpu_addr can be different from
page_address.

-aneesh