Re: get_user_pages() cache issues on ARM

Added James Bottomley to the CC. He designed this interface, and he
explained to me how it's supposed to work, but I since forgot.

James, do you have some memory of these issues?

Thanks,
Miklos

Hi Russell,

The get_user_pages() vs dcache coherency issue still seems to be
unresolved on ARM.

See flush_anon_page() and flush_kernel_dcache_page() in
Documentation/cachetlb.txt and their implementation on PARISC.

Can you please take a look at this?

I'm sorry, I don't think I have sufficient understanding of the Linux VM
to look at these issues anymore.

The questions I have are:

- where do these pages that get_user_pages() finds and calls flush_anon_page()
on come from?
- why is the current ARM flush_dcache_page() (which is also called after
flush_anon_page()) not sufficient?
- if we implement flush_anon_page() does that mean that we end up flushing
multiple times in some circumstances? If so, how do we avoid this?

I'm really serious - I no longer understand the Linux VM sufficiently to
get this stuff right.
-
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