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SubjectRE: Introducing paravirt_ops for x86_64
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Glauber de Oliveira Costa wrote:
> On 8/8/07, Nakajima, Jun <jun.nakajima@intel.com> wrote:
> > Glauber de Oliveira Costa wrote:
> > > Hi folks,
> > >
> > > After some time away from it, and a big rebase as a consequence,
here is
> > > the updated version of paravirt_ops for x86_64, heading to
inclusion.
> > >
> > > Your criticism is of course, very welcome.
> > >
> > > Have fun
> >
> > Do you assume that the kernel ougtht to use 2MB pages for its
mappings
> > (e.g. initilal text/data, direct mapping of physical memory) under
your
> > paravirt_ops? As far as I look at the patches, I don't find one.
>
> I don't think how it could be relevant here. lguest kernel does use
> 2MB pages, and it goes smootly. For 2MB pages, we will update the page
> tables in the very same way, and in the very places we did before.
> Just that the operations can now be overwritten.
>
> So, unless I'm very wrong, it only makes sense to talk about not
> supporting large pages in the guest level. But it is not a
> paravirt_ops problem.

Some MMU-related PV techiniques (including Xen, and direct paging mode
for Xen/KVM) need to write-protect page tables, avoiding to use 2MB
pages when mapping page tables. Looks like you did not, and that
exaplains why the patches are missing the relevant (many) paravirt_ops
in include/asm-x86_64/pgalloc.h, for example, compared with the i386
tree.

Jun
---
Intel Open Source Technology Center
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