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Re: [Xen-devel] Setting up page directories and tables

To: "Jeremy Fitzhardinge" <jeremy@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Setting up page directories and tables
From: "Dave Pacheco" <dap@xxxxxxxxxxxx>
Date: Tue, 1 May 2007 15:32:56 -0400
Cc: Joel Weinberger <joel@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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On 4/27/07, Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx> wrote:
I see from your description that you're pinning L1 pages.  That's
generally not how Xen linux kernels do it these days; they just pin the
whole pagetable from L2 down (in your non-PAE case).  Since pinning from
top-down is the same as loading cr3 from a validity-checking
perspective, it's useful to see if Xen likes your pagetables without
actually trashing them (if you load a bad cr3, you end up in limbo with
no useful pagetables, and Xen can't even print a useful stack backtrace
as it destroys your domain).

I don't really understand what you mean here. To "pin the whole pagetable from L2 down" - does that mean pinning the L2 pagetable page itself and then all of the L1 pages, or just the L2 pagetable page?

What exactly does pinning do? Does it simply ensure that the page won't be paged out and that Xen knows it's a page table? If that's the case, it seems like you still want to pin L1 pages so that you know that Xen is okay with your L1 page table.

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