Subject: Re: [PATCH 14/26] iommu/dma: Refactor iommu_dma_free

From: Christoph Hellwig <[email-masked]>
Date: Mon, 29 Apr 2019 21:16:22 +0200

On Mon, Apr 29, 2019 at 09:03:48PM +0200, Christoph Hellwig wrote:
> On Mon, Apr 29, 2019 at 02:59:43PM +0100, Robin Murphy wrote:
> > Hmm, I do still prefer my original flow with the dma_common_free_remap() 
> > call right out of the way at the end rather than being a special case in 
> > the middle of all the page-freeing (which is the kind of existing 
> > complexity I was trying to eliminate). I guess you've done this to avoid 
> > having "if (!dma_release_from_contiguous(...))..." twice like I ended up 
> > with, which is fair enough I suppose - once we manage to solve the new 
> > dma_{alloc,free}_contiguous() interface that may tip the balance so I can 
> > always revisit this then.
> 
> Ok, I'll try to accomodate that with a minor rework.

Does this look reasonable?

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 5b2a2bf44078..f884d22b1388 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -921,7 +921,7 @@ static void iommu_dma_free(struct device *dev, size_t size, void *cpu_addr,
 {
 	size_t alloc_size = PAGE_ALIGN(size);
 	int count = alloc_size >> PAGE_SHIFT;
-	struct page *page = NULL;
+	struct page *page = NULL, **pages = NULL;
 
 	__iommu_dma_unmap(dev, handle, size);
 
@@ -934,19 +934,17 @@ static void iommu_dma_free(struct device *dev, size_t size, void *cpu_addr,
 		 * If it the address is remapped, then it's either non-coherent
 		 * or highmem CMA, or an iommu_dma_alloc_remap() construction.
 		 */
-		struct page **pages = __iommu_dma_get_pages(cpu_addr);
-
-		if (pages)
-			__iommu_dma_free_pages(pages, count);
-		else
+		pages = __iommu_dma_get_pages(cpu_addr);
+		if (!pages)
 			page = vmalloc_to_page(cpu_addr);
-
 		dma_common_free_remap(cpu_addr, alloc_size, VM_USERMAP);
 	} else {
 		/* Lowmem means a coherent atomic or CMA allocation */
 		page = virt_to_page(cpu_addr);
 	}
 
+	if (pages)
+		__iommu_dma_free_pages(pages, count);
 	if (page && !dma_release_from_contiguous(dev, page, count))
 		__free_pages(page, get_order(alloc_size));
 }

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