linux-kernel - Re: [PATCH v2] mm: Introduce new function vm_insert_kmem

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Date:   Wed, 3 Oct 2018 13:00:03 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     linux@...linux.org.uk, miguel.ojeda.sandonis@...il.com,
        robin@...tonic.nl, stefanr@...6.in-berlin.de, hjc@...k-chips.com,
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        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
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Subject: Re: [PATCH v2] mm: Introduce new function vm_insert_kmem_page

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?