Message-ID: <54341F77.6060400@redhat.com>
Date: Tue, 07 Oct 2014 19:14:31 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
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Subject: Re: [PATCH 10/17] mm: rmap preparation for remap_anon_pages
References: <1412356087-16115-1-git-send-email-aarcange@redhat.com> <1412356087-16115-11-git-send-email-aarcange@redhat.com> <CA+55aFx++R42L75ooE=Fmaem73=V=q7f6pYTcALxgrA1y98G-A@mail.gmail.com> <20141006085540.GD2336@work-vm> <20141006164156.GA31075@redhat.com> <CA+55aFxAOYBny+QwXfkPy-P3rs-RPr5SLYLcPNBiFO3waBXtQA@mail.gmail.com> <20141007170731.GO2404@work-vm>
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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.

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