Re: [PATCH v2] mm: Introduce new function vm_insert_kmem_page

Matthew Wilcox
2018-10-03T20:00:03Z

On Thu, Oct 04, 2018 at 12:28:54AM +0530, Souptick Joarder wrote:
> These are the approaches which could have been taken to handle
> this scenario -
>
> * Replace vm_insert_page with vmf_insert_page and then write few
> extra lines of code to convert VM_FAULT_CODE to errno which
> makes driver users more complex ( also the reverse mapping errno to
> VM_FAULT_CODE have been cleaned up as part of vm_fault_t migration ,
> not preferred to introduce anything similar again)
>
> * Maintain both vm_insert_page and vmf_insert_page and use it in
> respective places. But it won't gurantee that vm_insert_page will
> never be used in #PF context.
>
> * Introduce a similar API like vm_insert_page, convert all non #PF
> consumer to use it and finally remove vm_insert_page by converting
> it to vmf_insert_page.
>
> And the 3rd approach was taken by introducing vm_insert_kmem_page().
>
> In short, vmf_insert_page will be used in page fault handlers
> context and vm_insert_kmem_page will be used to map kernel
> memory to user vma outside page fault handlers context.

As far as I can tell, vm_insert_kmem_page() is line-for-line identical
with vm_insert_page(). Seriously, here's a diff I just did:

-static int insert_page(struct vm_area_struct *vma, unsigned long addr,
- struct page *page, pgprot_t prot)
+static int insert_kmem_page(struct vm_area_struct *vma, unsigned long addr,
+ struct page *page, pgprot_t prot)
- /* Ok, finally just insert the thing.. */
-int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
+int vm_insert_kmem_page(struct vm_area_struct *vma, unsigned long addr,
- return insert_page(vma, addr, page, vma->vm_page_prot);
+ return insert_kmem_page(vma, addr, page, vma->vm_page_prot);
-EXPORT_SYMBOL(vm_insert_page);
+EXPORT_SYMBOL(vm_insert_kmem_page);

What on earth are you trying to do?