From: puck.chen@hisilicon•com (chenfeng)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] staging: ion: make the pte default none PTE_RDONLY
Date: Mon, 18 Jan 2016 11:44:54 +0800 [thread overview]
Message-ID: <569C5FB6.9000702@hisilicon.com> (raw)
In-Reply-To: <20160115232334.GD19062@n2100.arm.linux.org.uk>
On 2016/1/16 7:23, Russell King - ARM Linux wrote:
> On Fri, Jan 15, 2016 at 03:03:42PM -0800, Laura Abbott wrote:
>> (adding linux-arm and a few people)
>>
>> On 01/14/2016 06:42 PM, Chen Feng wrote:
>>> 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@hisilicon•com>
>>> Signed-off-by: Wei Dong <weidong2@hisilicon•com>
>>> Reviewed-by: Zhuangluan Su <suzhuangluan@hisilicon•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);
>>>
>>
>> The extra fault is unfortunate but I'm skeptical about just setting
>> pte_mkdirty.
>>
>> Catalin/Will, do you have any thoughts? Right now it seems like any
>> range mapped with remap_pfn_range will have this extra fault
>> behavior. Is marking the range dirty the best solution?
Laura Abbott,
I agree with you, it seems all the remap_pfn_range have this fault behavior.
>
> What happens if the mapping requested was read only - at the very
> least, I don't think this should be done unconditionally.
>
Russell,
I am not sure about doing this unconditionally, but it can waste memory&time
while handling page fault with ion alloced page.
And the page can be used directly.
prev parent reply other threads:[~2016-01-18 3:44 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1452825753-36364-1-git-send-email-puck.chen@hisilicon.com>
2016-01-15 23:03 ` [PATCH] staging: ion: make the pte default none PTE_RDONLY Laura Abbott
2016-01-15 23:23 ` Russell King - ARM Linux
2016-01-18 3:44 ` chenfeng [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=569C5FB6.9000702@hisilicon.com \
--to=puck.chen@hisilicon$(echo .)com \
--cc=linux-arm-kernel@lists$(echo .)infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox