Re: [PATCH] x86: create array based interface to change page attribute

Thomas Hellström
2008-04-01T21:30:32Z

Arjan van de Ven wrote:
> Thomas Hellström wrote:
>> Given this problem, the previously mentioned use-case, and the fact
>> that we mostly really use user-space mappings,
>> Is there a possibility we could add the following functions to Dave's
>> patch (provided they would work as intended, of course, namely
>> invalidate / bring back the kernel mapping).
>
> sadly there are multiple mappings, both in theory and practice.
> Especially the _np / _p functions specifically work on only the
> mapping you specify.
>
> For this to work we would need to somehow make a "mark all mappings
> NP, but please only do the kernel ones" kind of thing.
> The semantics of that are... lets say messy at best.
Hmm, I'm not sure I follow you here. Are you saying that it's illegal to
have an NP mapping of a page (which, If I understand it correctly, means
no mapping at all) at the same time as you have a, say user-space WC
mapping pointing to the same physical page?

Or are you saying that it's very hard to keep track of all mappings to a
page, and change only the ones you really want to change?

If you mean the latter, for the DRM case, the DRM memory manager has
already made sure all user-space mappings of a page are killed before
calling CPA on it, (using unmap_mapping_range()) and they are faulted
back once CPA is done.

I was under the impression that calling CPA on the kernel mapping of
that page would do the rest?

/Thomas