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Re: [Xen-devel] Question about monitor_table

To: Travis Johnson <tjohnson@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Question about monitor_table
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Tue, 14 Feb 2006 17:34:49 +0000
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On 14 Feb 2006, at 14:03, Travis Johnson wrote:

Could someone help me understand the need for the monitor page table. I
figure that arch_vcpu->guest_table points to a guests L2 page table (PD on x86) and arch_vcpu->shadow_table points to the guest_table's shadow table (if shadowing is turned on) but I don't quite get the purpose of the monitor_table. On x86_32 it seems like it just gets set to the value of the guest table on initialization and I lose track of it after that. I understand Xen needs to trap page table updates but I figured that would be a privileged operation and Xen could trap those accesses through hardware faults or by paravirtualizing through hypercalls (do_mmu_update).

That's a large amount of figuring so if someone could shed some light on the purpose and use of the monitor table I would appreciate it.

When running a fully-virtualised (HVM) guest, monitor_table is the pagetable that is used while Xen runs.

-- Keir

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