On Fri, Sep 21, 2018 at 2:56 AM Miguel Ojeda
<miguel.ojeda.sandonis@xxxxxxxxx> wrote:
>
> On Thu, Sep 20, 2018 at 10:23 PM, Souptick Joarder <jrdr.linux@xxxxxxxxx> wrote:
> > There is a plan to remove vm_insert_page permanently
> > and replace it with new API vmf_insert_page which will
> > return vm_fault_t type. As part of it vm_insert_page
> > is removed from this driver.
>
> A link to the discussion/plan would be nice. The commit 1c8f422059ae5
> ("mm: change return type to vm_fault_t") explains a bit, but has a
> broken link :( Googling for the stuff returns many of the patches, but
> not the actual discussion...
This might be helpful.
https://marc.info/?l=linux-mm&m=152054772413234&w=4
>
> > static int cfag12864bfb_mmap(struct fb_info *info, struct vm_area_struct *vma)
> > {
> > - return vm_insert_page(vma, vma->vm_start,
> > - virt_to_page(cfag12864b_buffer));
> > + struct page *page;
> > + unsigned long size = vma->vm_end - vma->vm_start;
> > +
> > + page = virt_to_page(cfag12864b_buffer);
> > + return remap_pfn_range(vma, vma->vm_start, page_to_pfn(page),
> > + size, vma->vm_page_prot);
>
> I am out of the loop on these mm changes, so please indulge me, but:
>
> * Why is there no documentation on vmf_insert_page() while
> vm_insert_page() had it? (specially since it seems you want to remove
> vm_insert_page()).
The plan is to convert vm_insert_{page,pfn,mixed} to
vmf_insert_{page,pfn,mixed}. As a good intermediate
steps inline wrapper vmf_insert_{pfn,page,mixed} are
introduced. After all the drivers converted, we will convert
vm_insert_page to vmf_insert_page and remove the inline
wrapper and update the document at the same time.
>
> * Shouldn't we have a simple remap_page() or remap_kernel_page() to
> fit this use case and avoid that dance? (another driver in auxdisplay
> will require the same change, and I guess others in the kernel as
> well).
There are few drivers similar like auxdisplay where straight forward
conversion from vm_insert_page to vmf_insert_page is not possible.
So I mapped the kernel memory to user vma using remap_pfn_range
and remove vm_insert_page in this driver.
Other way, is to replace vm_insert_page with vmf_insert_page() and
then convert VM_FAULT_CODE back to errno. But as part of vm_fault_t
migration we have already removed/cleanup most the errno to VM_FAULT_CODE
mapping from drivers. So I prefer not to take this option.
Third, we can introduce a similar API like vm_insert_page say,
vm_insert_kmem_page() and use it for same scenarios like this.
If there is a better way to do this, we can discuss it.
