Re: ioremap_page_range: remapping of physical RAM ranges

[John Hubbard <jhubbard@nvidia.com>]

On 01/25/2017 11:55 AM, A. Samy wrote:
> Hi,
>
> Commit 3277953de2f31 un-exported ioremap_page_range(), what is an
> alternative method of remapping a physical ram range...  This function
> was very useful, examples here:
> https://github.com/asamy/ksm/blob/master/mm.c#L38 and here:
> https://github.com/asamy/ksm/blob/master/ksm.c#L410 etc...
>
> So, you're forcing me to either reimplement it on my own (which is
> merely copy-pasting the kernel function), unless you have a suggestion
> on what else to use (which I could never find other)?

Hi A. Samy,

I'm sorry this caught you by surprise, let's try get your use case covered.

My thinking on this was: the exported ioremap* family of functions was clearly intended to provide 
just what the name says: mapping of IO (non-RAM) memory. If normal RAM is to be re-mapped, then it 
should not be done "casually" in a driver, as a (possibly unintended) side effect of a function that 
implies otherwise. Either it should be done within the core mm code, or perhaps a new, better-named 
wrapper could be provided, for cases such as yours.

After a very quick peek at your github code, it seems that your mm_remap() routine already has some 
code in common with __ioremap_caller(), so I'm thinking that we could basically promote your 
mm_remap to the in-tree kernel and EXPORT it, and maybe factor out the common parts (or not--it's 
small, after all). Thoughts? If you like it, I'll put something together here.

thanks
john h

>
> Thanks,
>
> -- 
> asamy
>
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