From: gavinli@thegavinli.com
To: Christoph Hellwig <hch@lst.de>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
iommu@lists.linux-foundation.org
Cc: Gavin Li <git@thegavinli.com>
Subject: [PATCH v1] dma-mapping: normal memory for mmap() on coherent architectures
Date: Fri, 2 Aug 2019 11:07:58 -0700 [thread overview]
Message-ID: <20190802180758.9691-1-gavinli@thegavinli.com> (raw)
From: Gavin Li <git@thegavinli.com>
On x86, calling dma_mmap_coherent() on memory allocated with
dma_alloc_coherent() causes the following warning to be issued:
x86/PAT: ... map pfn RAM range req uncached-minus for [mem 0x77f000000-0x77f210fff], got write-back
This occurs because on x86 dma_alloc_coherent() returns normal kernel
memory pages (with a write-back PAT), but dma_mmap_coherent() tries to
map the same pages into userspace with a uncached-minus PAT, even though
there is no need for the mapping to noncached.
This patch ensures that on DMA coherent architectures/devices, memory is
mapped normally rather than as noncached.
Signed-off-by: Gavin Li <git@thegavinli.com>
---
include/linux/dma-noncoherent.h | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
index 9741767e400f..40ff11380ec7 100644
--- a/include/linux/dma-noncoherent.h
+++ b/include/linux/dma-noncoherent.h
@@ -31,7 +31,11 @@ long arch_dma_coherent_to_pfn(struct device *dev, void *cpu_addr,
pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
unsigned long attrs);
#else
-# define arch_dma_mmap_pgprot(dev, prot, attrs) pgprot_noncached(prot)
+static inline pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
+ unsigned long attrs)
+{
+ return dev_is_dma_coherent(dev) ? prot : pgprot_noncached(prot);
+}
#endif
#ifdef CONFIG_DMA_NONCOHERENT_CACHE_SYNC
--
2.22.0
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next reply other threads:[~2019-08-02 20:08 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-02 18:07 gavinli [this message]
2019-08-03 6:23 ` [PATCH v1] dma-mapping: normal memory for mmap() on coherent architectures Christoph Hellwig
2019-08-03 6:35 ` Gavin Li
2019-08-03 6:39 ` Christoph Hellwig
2020-10-28 11:39 ` Oded Gabbay
2020-10-28 17:31 ` Christoph Hellwig
2020-10-28 17:38 ` Oded Gabbay
2020-10-28 17:39 ` Christoph Hellwig
2020-10-28 19:33 ` Oded Gabbay
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