linux-kernel - [PATCH] swiotlb: Replace kmap_atomic() with memcpy_{from,to}

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Date:   Thu,  1 Sep 2022 15:29:06 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Christoph Hellwig <hch@...radead.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Ira Weiny <ira.weiny@...el.com>
Subject: [PATCH] swiotlb: Replace kmap_atomic() with memcpy_{from,to}_page()

The use of kmap_atomic() is being deprecated in favor of
kmap_local_page(), which can also be used in atomic context (including
interrupts).

Replace kmap_atomic() with kmap_local_page(). Instead of open coding
mapping, memcpy(), and un-mapping, use the memcpy_{from,to}_page() helper.

Suggested-by: Ira Weiny <ira.weiny@...el.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
---
 kernel/dma/swiotlb.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index c5a9190b218f..a28ac23ad8db 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -549,9 +549,8 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size
 	}
 
 	if (PageHighMem(pfn_to_page(pfn))) {
-		/* The buffer does not have a mapping.  Map it in and copy */
 		unsigned int offset = orig_addr & ~PAGE_MASK;
-		char *buffer;
+		struct page *page;
 		unsigned int sz = 0;
 		unsigned long flags;
 
@@ -559,12 +558,11 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size
 			sz = min_t(size_t, PAGE_SIZE - offset, size);
 
 			local_irq_save(flags);
-			buffer = kmap_atomic(pfn_to_page(pfn));
+			page = pfn_to_page(pfn);
 			if (dir == DMA_TO_DEVICE)
-				memcpy(vaddr, buffer + offset, sz);
+				memcpy_from_page(vaddr, page, offset, sz);
 			else
-				memcpy(buffer + offset, vaddr, sz);
-			kunmap_atomic(buffer);
+				memcpy_to_page(page, offset, vaddr, sz);
 			local_irq_restore(flags);
 
 			size -= sz;
-- 
2.37.2