linux-kernel - [PATCH v2 1/2] iommu/dma: Respect __GFP_DMA and __GFP

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Message-Id: <20170704135556.21704-1-tfiga@chromium.org>
Date:   Tue,  4 Jul 2017 22:55:55 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     iommu@...ts.linux-foundation.org
Cc:     linux-kernel@...r.kernel.org, Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Tomasz Figa <tfiga@...omium.org>
Subject: [PATCH v2 1/2] iommu/dma: Respect __GFP_DMA and __GFP_DMA32 in incoming GFP flags

Current implementation of __iommu_dma_alloc_pages() keeps adding
__GFP_HIGHMEM to GFP flags regardless of whether other zone flags are
already included in the incoming flags. If __GFP_DMA or __GFP_DMA32 is
set at the same time as __GFP_HIGHMEM, the allocation fails due to
invalid zone flag combination.

Fix this by checking for __GFP_DMA and __GFP_DMA32 in incoming GFP flags
and adding __GFP_HIGHMEM only if they are not present.

Signed-off-by: Tomasz Figa <tfiga@...omium.org>
---
 drivers/iommu/dma-iommu.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Changes from v1:
 - Update the comment as per Robin's suggestion.

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 9d1cebe7f6cb..bf23989b5158 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -445,8 +445,14 @@ static struct page **__iommu_dma_alloc_pages(unsigned int count,
 	if (!pages)
 		return NULL;
 
-	/* IOMMU can map any pages, so himem can also be used here */
-	gfp |= __GFP_NOWARN | __GFP_HIGHMEM;
+	/*
+	 * Unless we have some addressing limitation implied by GFP_DMA flags,
+	 * assume the IOMMU can map all of RAM and we can allocate anywhere.
+	 */
+	if (!(gfp & (__GFP_DMA | __GFP_DMA32)))
+		gfp |= __GFP_HIGHMEM;
+
+	gfp |= __GFP_NOWARN;
 
 	while (count) {
 		struct page *page = NULL;
-- 
2.13.2.725.g09c95d1e9-goog