Re: Should we delete memmove_page?

[Matthew Wilcox <willy@infradead.org>]

On Thu, May 26, 2022 at 05:40:44PM -0700, Ira Weiny wrote:
> On Thu, May 26, 2022 at 03:48:28PM +0100, Matthew Wilcox wrote:
> > 
> > I was looking at memmove_page() and it occurred to me that it can't
> > actually work,
> 
> Oh wow yea.  Because you can't unmap that address correctly.

I don't understand what you mean ... you can unmap the address, it's
just that memmove can't know that the two virtual ranges actually
overlap physically.

> Yes deletion is best.  But...
> 
> 	copy_user_highpage()
> 	copy_highpage()
> 
> ... might suffer from the same potential issue should a user not realize.  I
> think memcpy_page() by virtue of the name.

Umm?  They're all using memcpy(), so the caller must guarantee that the
physical addresses are different.

> I could not say anything at LSFmm because the Outreachy interns had not been
> announced but I've selected Fabio to help with the highmem rework through that
> program.

Excellent!  I advised Fabio last year, and I think he'll do a sterling
job this year.

> Would you like Fabio or I to send a patch?  I think the main thing right now is
> to just drop the memmove_page()

Sure, just stick my Reported-by: on it.