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xen-devel
Re: [Xen-devel] Re: Next steps with pv_ops for Xen
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To: |
Derek Murray <Derek.Murray@xxxxxxxxxxxx> |
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Subject: |
Re: [Xen-devel] Re: Next steps with pv_ops for Xen |
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From: |
Gerd Hoffmann <kraxel@xxxxxxxxxx> |
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Date: |
Mon, 03 Dec 2007 15:16:24 +0100 |
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Cc: |
"xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Eduardo Habkost <ehabkost@xxxxxxxxxx>, Juan Quintela <quintela@xxxxxxxxxx>, "Stephen C. Tweedie" <sct@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>, Glauber de Oliveira Costa <gcosta@xxxxxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, "virtualization@xxxxxxxxxxxxxx" <virtualization@xxxxxxxxxxxxxx> |
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Mon, 03 Dec 2007 06:17:35 -0800 |
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Thunderbird 2.0.0.9 (X11/20071115) |
Derek Murray wrote:
> I take the blame for that one. I added the hook because, if a process
> were to die whilst holding one or more grants, there were no hooks that
> would make it possible to carry out the grant-unmap. All existing hooks
> on either the device or the VMA were called *after* the PTEs were cleared.
Hmm. What exactly is the issue here?
This is about *userspace* mappings, right? As far as I can see from a
quick scan there of the code is an additional kernel space mapping for
the grants and the userspace mapping is optional. I don't see any
problems with userspace mapping going away without *instant*
notification. Cleaning up a bit later, called from the
file_ops->release callback maybe, should work ok.
The problem I see with the additional vm_ops callback is that I suspect
you'll have to come up with some *very* good arguments to get it
accepted by the VM (as in "virtual memory") folks and merged mainline.
> It gets better, though. The same hook is used in the version of blktap
> in linux-2.6.18-xen (not, as far as I can see, in the sparse tree for
> xen-3.1-testing):
Oh, I'm thinking more in the direction of killing blktap altogether in
favor of a pure userspace implementation on top of gntdev.
cheers,
Gerd
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