Re: [PATCH] staging: ion: make the pte default none PTE_RDONLY
From: Russell King - ARM Linux
Date: Fri Jan 15 2016 - 18:24:25 EST
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
> > 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@xxxxxxxxxxxxx>
> >Signed-off-by: Wei Dong <weidong2@xxxxxxxxxxxxx>
> >Reviewed-by: Zhuangluan Su <suzhuangluan@xxxxxxxxxxxxx>
> > 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
> 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?
What happens if the mapping requested was read only - at the very
least, I don't think this should be done unconditionally.
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