Xen devel - Mar 2007 - Guest page table dumping

Hello List,

I''m trying to get at the guest''s (x86_64 VMX HVM guest, x86_64
Xen 3.0.4-1)
view of the page tables and dump them out so I can read them offline. My
strategy to do this is to add a domctl I can use to map the domain page that
corresponds to the guest''s page table page (for right now just the top
level
page table, PML4) then dump out that page to dom0 so I can process it.
I''ve
got the skeleton domctl working but the trouble is I don''t know exactly
how
I should transform the guests view of the CR3 address in order for
map_domain_page() to be happy.

What transformation should I use to get vmx.cpu_cr3 into a happy address for
use with map_domain_page(). My best guess so far is
map_domain_page(gmfn_to_mfn(d, v->arch.hvm_cpu.u.vmx.cpu_cr3 >>
PAGE_SHIFT)), is that in the ballpark?

Is cpu_cr3 the correct cr3 to use to get at the level 4 guest page table?

Would it be easier to dump the shadow representation of the l4 page table?

TIA,
-Travis


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Hi Travis,

At 14:46 -0400 on 16 Mar (1174056385), Travis Johnson
wrote:
> I''ve
> got the skeleton domctl working but the trouble is I don''t know
exactly how
> I should transform the guests view of the CR3 address in order for
> map_domain_page() to be happy.
Have a read through sh_update_cr3(); near the top it calls
hvm_get_guest_ctrl_reg(v, 3) to read the guest''s CR3 and translates it
to a guest frame-number and then to a machine frame-number (suitable for
map_domain_page())
> Is cpu_cr3 the correct cr3 to use to get at the level 4 guest page table?
Yes, though calling hvm_get_guest_ctrl_reg() would be cleaner.
 
> Would it be easier to dump the shadow representation of the l4 page table?
You can get that at v->arch.shadow_table[0] for 64bit guests.

There''s also some code in svm.c for dumping page tables, but it may
have
bit-rotted.

Cheers,

Tim.

-- 
Tim Deegan <Tim.Deegan@xensource.com>, XenSource UK Limited
Registered office c/o EC2Y 5EB, UK; company number 05334508

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