linux-kernel - [PATCH v3 1/5] x86: make dma_alloc_coherent() return zeroed memory if CMA is enabled

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Message-Id: <1397567329-3771-2-git-send-email-akinobu.mita@gmail.com>
Date:	Tue, 15 Apr 2014 22:08:45 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Cc:	Akinobu Mita <akinobu.mita@...il.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Don Dutile <ddutile@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	x86@...nel.org, iommu@...ts.linux-foundation.org
Subject: [PATCH v3 1/5] x86: make dma_alloc_coherent() return zeroed memory if CMA is enabled

Calling dma_alloc_coherent() with __GFP_ZERO must return zeroed memory.

But when the contiguous memory allocator (CMA) is enabled on x86 and
the memory region is allocated by dma_alloc_from_contiguous(), it
doesn't return zeroed memory.  Because dma_generic_alloc_coherent()
forgot to fill the memory region with zero if it was allocated by
dma_alloc_from_contiguous()

Most implementations of dma_alloc_coherent() return zeroed memory
regardless of whether __GFP_ZERO is specified.  So this fixes it by
unconditionally zeroing the allocated memory region.

Alternatively, we could fix dma_alloc_from_contiguous() to return
zeroed out memory and remove memset() from all caller of it.  But we
can't simply remove the memset on arm because __dma_clear_buffer() is
used there for ensuring cache flushing and it is used in many places.
Of course we can do redundant memset in dma_alloc_from_contiguous(),
but I think this patch is less impact for fixing this problem.

Cc: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Don Dutile <ddutile@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Andi Kleen <andi@...stfloor.org>
Cc: x86@...nel.org
Cc: iommu@...ts.linux-foundation.org
Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
---
* Change from v2
- update commit log to describe a possible alternative fix

 arch/x86/kernel/pci-dma.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index f7d0672..a0ffe44 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -97,7 +97,6 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t size,

 	dma_mask = dma_alloc_coherent_mask(dev, flag);

-	flag |= __GFP_ZERO;
 again:
 	page = NULL;
 	/* CMA can be used only in the context which permits sleeping */
@@ -120,7 +119,7 @@ again:

 		return NULL;
 	}
-
+	memset(page_address(page), 0, size);
 	*dma_addr = addr;
 	return page_address(page);
 }
-- 
1.8.3.2

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