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xen-devel
RE: [Xen-devel] Two shadow page tables for HVM
Not sure it will help what-so-ever, but if you look up any posts that I've
made to this list and some of their responses, you'll get "some" information
related to this topic.
I'd love to hear answers to this post.
Take care,
Sina
-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Emre Can Sezer
Sent: Wednesday, December 17, 2008 6:06 PM
To: Xen Devel
Subject: [Xen-devel] Two shadow page tables for HVM
Hi,
As part of my research I am going to play around with page permissions.
However, I might have to do this pretty often, so I'm thinking about
having two page tables that are synchronized and only differ in their
permissions. The idea is to have a set of permissions when code block A
is being executed and another set when block B is being executed. I
plan to capture execution jumps by specifying the inactive block as
non-executable.
I am running a HVM guest on a x86_64 machine. I'm only interested in
kernel pages, in that I don't have to have a second page table for user
level pages as their permissions will be the same.
So far I can think of only two ways of doing this. First, I can have
two top level shadow page tables and use one of the unused slots in
struct arch_domain to store this page. Then I modify
propagate_l*e_from_guest functions to ensure that they create and
synchronize the second page table. Second, I can have pages that are
twice as large as original page tables. I'm not sure what the
implications are concerning shadow cache and the linear page table
mappings.
Which one of these methods would be easier to implement? Is there an
easier way of having two sets of page tables? If I had the means, would
it be worth switching to AMD for the NPT?
Thanks in advance,
John
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