linux-kernel - [PATCH 09/10] iommu: Fix MAX_ORDER usage in __iommu_dma_alloc

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Date:   Wed, 15 Mar 2023 14:31:32 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>
Cc:     linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Robin Murphy <robin.murphy@....com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: [PATCH 09/10] iommu: Fix MAX_ORDER usage in __iommu_dma_alloc_pages()

MAX_ORDER is not inclusive: the maximum allocation order buddy allocator
can deliver is MAX_ORDER-1.

Fix MAX_ORDER usage in __iommu_dma_alloc_pages().

Also use GENMASK() instead of hard to read "(2U << order) - 1" magic.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Robin Murphy <robin.murphy@....com>
Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>
---
 drivers/iommu/dma-iommu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 99b2646cb5c7..ac996fd6bd9c 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -736,7 +736,7 @@ static struct page **__iommu_dma_alloc_pages(struct device *dev,
 	struct page **pages;
 	unsigned int i = 0, nid = dev_to_node(dev);
 
-	order_mask &= (2U << MAX_ORDER) - 1;
+	order_mask &= GENMASK(MAX_ORDER - 1, 0);
 	if (!order_mask)
 		return NULL;
 
@@ -756,7 +756,7 @@ static struct page **__iommu_dma_alloc_pages(struct device *dev,
 		 * than a necessity, hence using __GFP_NORETRY until
 		 * falling back to minimum-order allocations.
 		 */
-		for (order_mask &= (2U << __fls(count)) - 1;
+		for (order_mask &= GENMASK(__fls(count), 0);
 		     order_mask; order_mask &= ~order_size) {
 			unsigned int order = __fls(order_mask);
 			gfp_t alloc_flags = gfp;
-- 
2.39.2