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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 13:41:04 +0100
Cc: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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Thread-index: AcWkt3Cu9FDkZ4M2SPaZ8ap5p+ptBwAAozCA
Thread-topic: [Xen-devel] passing hypercall parameters by pointer
> This is all potentially fixable before 3.0 final. Paravirt 
> x86 can continue to use guest virtual addresses. The idea 
> would be that the registration scheme would essentially 
> create a parameter-passing 'address space' into which you 
> hook pages of memory. On x86 we would map the address space 
> onto regions of kernel va space. On other arches we would map 
> the address space onto physical addresses that get mapped 
> into Xen's va space. 
> get_user/put_user/copy_from_user/copy_to_user will take guest 
> addresses that point into this parameter-passing address space.
> At least we can scope it out by doing a few hypercalls to 
> start with -- probably dom0_ops first and see how it pans 
> out. I think it will work quite well...

I'd be inclined to first go after the ops that are needed for the
paravirtualized drivers (mem_op, grantab_op). Perhaps people could post
a few patch examples for dicsussion?

NB: This in no way represents a commitment to get this into 3.0-final.
Let's have a look at the patches and decide.

[Right now, anything that isn't fixing bugs or sorting out xenbus/tools
is actually a distraction]


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