Re: [Qemu-devel] [PATCH 10/17] mm: rmap preparation for remap_anon_pages

[Paolo Bonzini]

Il 07/10/2014 19:07, Dr. David Alan Gilbert ha scritto:
>> > 
>> > So I'd *much* rather have a "write()" style interface (ie _copying_
>> > bytes from user space into a newly allocated page that gets mapped)
>> > than a "remap page" style interface
> Something like that might work for the postcopy case; it doesn't work
> for some of the other uses that need to stop a page being changed by the
> guest, but then need to somehow get a copy of that page internally to QEMU,
> and perhaps provide it back later.

I cannot parse this.  Which uses do you have in mind?  Is it for
QEMU-specific or is it for other applications of userfaults?

As long as the page is atomically mapped, I'm not sure what the
difference from remap_anon_pages are (as far as the destination page is
concerned).  Are you thinking of having userfaults enabled on the source
as well?

Paolo

> remap_anon_pages worked for those cases
> as well; I can't think of another current way of doing it in userspace.