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RE: [Xen-devel] Re: user/hypervisor address space solution

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Subject: RE: [Xen-devel] Re: user/hypervisor address space solution
From: Hollis Blanchard <hollisb@xxxxxxxxxx>
Date: Sat, 18 Feb 2006 09:24:31 +1100
Cc: Dan Magenheimer <dan.magenheimer@xxxxxx>, Jimi Xenidis <jimix@xxxxxxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Fri, 2006-02-17 at 17:05 +0800, Tian, Kevin wrote:
> >From: Hollis Blanchard
> >Sent: 2006年2月14日 19:13
> >
> >I don't know what implications this could have for ia64, since they
> suck
> >in so much Linux code... but perhaps that Linux code isn't the stuff
> >that deals with userland, so might not have uaccess users.
> Regarding this area to access domain parameters, IA64 should be OK
> since xen/ia64 shares same virtual address space (i.e same ASN) with
> domain, thus able to access pointer passed in directly. Linux style
> uaccess interfaces can easily work for xen/ia64 in this aspect.

Actually I was referring to the API rename, not the underlying
implementation. But since then I've changed my mind, and I'm fine with
leaving e.g. "put_user" around, as long as nobody calls it from common
code. So if there are put_user() callers in the Linux code you suck in,
it will still be ok.

But while we're on the subject, I recall hearing that IA64 has an issue
with TLB faults when accessing domain virtual addresses. Could you
elaborate on that? I guess you're using a software-controlled TLB, and
when a fault occurs you need to call up to Linux to handle it?

Hollis Blanchard
IBM Linux Technology Center

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