Follow Techotopia on Twitter

On-line Guides
All Guides
eBook Store
iOS / Android
Linux for Beginners
Office Productivity
Linux Installation
Linux Security
Linux Utilities
Linux Virtualization
Linux Kernel
System/Network Admin
Scripting Languages
Development Tools
Web Development
GUI Toolkits/Desktop
Mail Systems
Eclipse Documentation

How To Guides
General System Admin
Linux Security
Linux Filesystems
Web Servers
Graphics & Desktop
PC Hardware
Problem Solutions
Privacy Policy




Xen 3.0 Virtualization Interface Guide
Prev Home Next

3.3 Page Table Updates

In the default mode of operation, Xen enforces read-only access to page tables and requires guest operating systems to explicitly request any modifications. Xen validates all such requests and only applies updates that it deems safe. This is necessary to prevent domains from adding arbitrary mappings to their page tables.

To aid validation, Xen associates a type and reference count with each memory page. A page has one of the following mutually-exclusive types at any point in time: page directory (PD), page table ( PT), local descriptor table (LDT), global descriptor table (GDT), or writable (RW). Note that a guest OS may always create readable mappings of its own memory regardless of its current type.

This mechanism is used to maintain the invariants required for safety; for example, a domain cannot have a writable mapping to any part of a page table as this would require the page concerned to simultaneously be of types PT and RW.

mmu_update(mmu_update_t *req, int count, int *success_count, domid_t domid)

This hypercall is used to make updates to either the domain's pagetables or to the machine to physical mapping table. It supports submitting a queue of updates, allowing batching for maximal performance. Explicitly queuing updates using this interface will cause any outstanding writable pagetable state to be flushed from the system.

Xen 3.0 Virtualization Interface Guide
Prev Home Next

  Published under the terms of the GNU General Public License Design by Interspire