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RE: [Xen-devel] passing hypercall parameters by pointer

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, "Jimi Xenidis" <jimix@xxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] passing hypercall parameters by pointer
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Fri, 19 Aug 2005 12:34:21 +0100
Cc: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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Thread-index: AcWkqMCA1hpyDUE5SUiLP5suDaszzwACBalA
Thread-topic: [Xen-devel] passing hypercall parameters by pointer
> The current mlock() scheme in libxc is screwed anyway -- we 
> mlock/munlock regions that may overlap at page granularity. 
> Fixing this would lead naturally to a preallocation scheme.

That's a very good point. For the moment, we should remove all the
munlock() calls for safety. The amount of unnecessary memory we'll end
up pinning will be tiny, so we shouldn't worry about it.

Post 3.0 we can completely redo the dom0 op interface, but the rest of
the hypercall interface will have to remain backward compatible, at
least for x86_*. Since passing by VA is so convenient on the
architectures that support it we may not want to do anything different
on these anyhow.

For VT paravirt drivers I think pre-registration will work fine. The set
of hypercalls we need to support is small anyhow.


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