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Introduce dmam_zalloc_coherent()

PATCH In review Michael Moese 4 participants 4 messages Aug 8, 2017 – Aug 10, 2017 DMA mapping helpers

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Michael Moese

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#0 lore raw

PATCH 1/1 Introduce dmam_zalloc_coherent()

All memory allocation functions have a pendant for allocating zeroed memory, but dmam_alloc_coherent does not have such a pendant. However, it is easier to read dmam_zalloc_coherent than passing an extra flag or, even worse, see memset() after the allocation.
This patch adds an inline function dmam_zalloc_coherent(), exactly like the implementation of dma_zalloc_coherent().

Signed-off-by Michael Moese <[email protected]>
---
 include/linux/dma-mapping.h | 9 +++++++++
 1 file changed, 9 insertions(+)
include/linux/dma-mapping.h +9 -0
index 03c0196a6f24..cf6cbda76ee2 100644
@@ -761,6 +761,15 @@ extern void dmam_free_coherent(struct device *dev, size_t size, void *vaddr,
 extern void *dmam_alloc_attrs(struct device *dev, size_t size,
 			      dma_addr_t *dma_handle, gfp_t gfp,
 			      unsigned long attrs);
+
+static inline void *dma_zalloc_coherent(struct device *dev, size_t size,
+					dma_addr_t *dma_handle, gfp_t flag)
+{
+	void *ret = dmam_alloc_coherent(dev, size, dma_handle,
+					flag | __GFP_ZERO);
+	return ret;
+}
+
 #ifdef CONFIG_HAVE_GENERIC_DMA_COHERENT
 extern int dmam_declare_coherent_memory(struct device *dev,
 					phys_addr_t phys_addr,
Signature · 1 line
2.13.1
#1 lore raw
Quoted 6 lines · Michael Moese

All memory allocation functions have a pendant for allocating zeroed memory, but dmam_alloc_coherent does not have such a pendant. However, it is easier to read dmam_zalloc_coherent than passing an extra flag or, even worse, see memset() after the allocation.
This patch adds an inline function dmam_zalloc_coherent(), exactly like the implementation of dma_zalloc_coherent().

I'm a bit worried about the __GFP_ZERO as we have lots of non-kmalloc implementations of these. But on the other hand we already implement dma_zalloc_coherent the same way, which means we'd already buggy.

So I plan to apply this for 4.14, but I also plan to spend some time to implement all the existin alloc ops to make sure it's going to work fine.

maintainer
#2 lore raw

Hi Christoph,

Quoted 7 lines · Christoph Hellwig
Quoted 6 lines · Michael Moese

All memory allocation functions have a pendant for allocating zeroed memory, but dmam_alloc_coherent does not have such a pendant. However, it is easier to read dmam_zalloc_coherent than passing an extra flag or, even worse, see memset() after the allocation.
This patch adds an inline function dmam_zalloc_coherent(), exactly like the implementation of dma_zalloc_coherent().

Quoted 7 lines

I'm a bit worried about the __GFP_ZERO as we have lots of non-kmalloc implementations of these. But on the other hand we already implement dma_zalloc_coherent the same way, which means we'd already buggy.

So I plan to apply this for 4.14, but I also plan to spend some time to implement all the existin alloc ops to make sure it's going to work fine.

Frankly, since introducing dma_mmap_coherent, dma_alloc_coherent already clears allocated buffers to avoid potential information leak to userspace. There are even drivers that rely on such behavior, see
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-April/338804.html

Maybe it would make sense to properly document it and then convert dma_zalloc* to standard dma_alloc_* calls?

Best regards

Signature · 2 lines
Marek Szyprowski, PhD
Samsung R&D Institute Poland
build bot
#3 lore raw
In reply to Michael Moese
url: https://github.com/0day-ci/linux/commits/Michael-Moese/Introduce-dmam_zalloc_coherent/20170810-011949 config: i386-tinyconfig (attached as .config) compiler: gcc-6 (Debian 6.2.0-3) 6.2.0…

Hi Michael,

[auto build test ERROR on linus/master]
[also build test ERROR on v4.13-rc4 next-20170808]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url: https://github.com/0day-ci/linux/commits/Michael-Moese/Introduce-dmam_zalloc_coherent/20170810-011949
config: i386-tinyconfig (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901 reproduce:

        # save the attached .config to linux build tree
        make ARCH=i386

All errors (new ones prefixed by >>):

In file included from include/linux/skbuff.h:34:0,

                    from include/net/net_namespace.h:34,
                    from include/linux/inet.h:46,
                    from include/linux/sunrpc/msg_prot.h:203,
                    from include/linux/sunrpc/auth.h:15,
                    from include/linux/nfs_fs.h:29,
                    from init/do_mounts.c:32:
>> include/linux/dma-mapping.h:765:21: error: redefinition of 'dma_zalloc_coherent'

static inline void *dma_zalloc_coherent(struct device *dev, size_t size,
^~~~~~~~~~~~~~~~~~~
include/linux/dma-mapping.h:691:21: note: previous definition of 'dma_zalloc_coherent' was here
static inline void *dma_zalloc_coherent(struct device *dev, size_t size,
^~~~~~~~~~~~~~~~~~~

vim +/dma_zalloc_coherent +765 include/linux/dma-mapping.h

753
754 /*
755 * Managed DMA API
756 */
757 extern void *dmam_alloc_coherent(struct device *dev, size_t size,
758 dma_addr_t *dma_handle, gfp_t gfp);
759 extern void dmam_free_coherent(struct device *dev, size_t size, void *vaddr,
760 dma_addr_t dma_handle);
761 extern void *dmam_alloc_attrs(struct device *dev, size_t size,
762 dma_addr_t *dma_handle, gfp_t gfp,
763 unsigned long attrs);
764

 > 765	static inline void *dma_zalloc_coherent(struct device *dev, size_t size,

766 dma_addr_t *dma_handle, gfp_t flag)
767 {
768 void *ret = dmam_alloc_coherent(dev, size, dma_handle,
769 flag | __GFP_ZERO);
770 return ret;
771 }
772

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