linux-kernel - [PATCH] staging: ion: make the pte default none PTE

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Date:	Fri, 15 Jan 2016 10:42:33 +0800
From:	Chen Feng <puck.chen@...ilicon.com>
To:	<gregkh@...uxfoundation.org>, <arve@...roid.com>,
	<riandrews@...roid.com>, <paul.gortmaker@...driver.com>,
	<labbott@...hat.com>, <gioh.kim@....com>, <tranmanphong@...il.com>,
	<mitchelh@...eaurora.org>, <devel@...verdev.osuosl.org>,
	<linux-kernel@...r.kernel.org>, <puck.chen@...ilicon.com>,
	<yudongbin@...ilicon.com>, <saberlily.xia@...ilicon.com>,
	<suzhuangluan@...ilicon.com>, <kong.kongxinwei@...ilicon.com>,
	<xuyiping@...ilicon.com>, <z.liuxinliang@...ilicon.com>,
	<weidong2@...ilicon.com>, <w.f@...wei.com>,
	<puck.chen@...mail.com>, <shimingxing@...ilicon.com>,
	<oliver.fu@...ilicon.com>, <albert.lubing@...ilicon.com>,
	<chenxiang9@...wei.com>, <liuzixing@...wei.com>,
	<haojian.zhuang@...aro.org>
CC:	<qijiwen@...ilicon.com>, <peter.panshilin@...ilicon.com>,
	<dan.zhao@...ilicon.com>, <linuxarm@...wei.com>,
	<dev@...ts.96boards.org>
Subject: [PATCH] staging: ion: make the pte default none PTE_RDONLY

The page is already alloc at ion_alloc function,
ion_mmap map the alloced pages to user-space.

The default prot can be PTE_RDONLY. Take a look at
here:
set_pte_at()
arch/arm64/include/asm:
		if (pte_dirty(pte) && pte_write(pte))
			pte_val(pte) &= ~PTE_RDONLY;
		else
			pte_val(pte) |= PTE_RDONLY;

So with the dirty bit,it can improve the efficiency
and donnot need to handle memory fault when use access.

Signed-off-by: Chen Feng <puck.chen@...ilicon.com>
Signed-off-by: Wei Dong <weidong2@...ilicon.com>
Reviewed-by: Zhuangluan Su <suzhuangluan@...ilicon.com>
---
 drivers/staging/android/ion/ion.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index e237e9f..dba5942 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -1026,6 +1026,9 @@ static int ion_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
 	if (!(buffer->flags & ION_FLAG_CACHED))
 		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
 
+	/*Default writeable*/
+	vma->vm_page_prot = pte_mkdirty(vma->vm_page_prot);
+
 	mutex_lock(&buffer->lock);
 	/* now map it to userspace */
 	ret = buffer->heap->ops->map_user(buffer->heap, buffer, vma);
-- 
1.9.1