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.