On Wednesday 11 December 2013 23:03:05 Jack Ramien wrote: > Hi All, > > When "Enable Nested Paging" is selected in the VM setting, does it mean > that VBox will use nested paging provided that host OS supports it or does > it mean that host OS is already supporting this feature? Is there a way to > confirm if virtual box is using nested page table support by examining the > code path?
there are two related CPU capabilities: VT-x/AMD-V and nested paging. The latter depends on the former. There is no OS support for nested paging required, only the CPU needs to support it. But the OS needs to provide a tiny bit of support for VT-x/AMD-V: It must not disable this feature, because once disabled it cannot be enabled by software until the host is rebooted. If you are able to enable VT-x/AMD-V in the GUI then this means that VT-x or AMD-V is available on your host. If not available, the corresponding VM setting is not available (disabled). If VT-x is available then you can also enable nested paging in the VM settings. But at this time it is not guaranteed that the guest will really use this CPU feature. You can only check if nested paging is used by looking at the VBox.log file or by looking at the runtime settings in the VM information dialog (HostKey+N while the VM is running). Determining if nested paging is available is more difficult than determining if VT-x/AMD-V is available because the latter capability can be detected by executing the unprivileged cpuid instruction while the former capability can be only detected by reading an MSR which is a privileged operation (can only be executed at kernel level). Since 4.3 it would be possible to determine the presence of nested paging from the VirtualBox selector application but the selector does not make use of the interface yet. Kind regards, Frank -- Dr.-Ing. Frank Mehnert | Software Development Director, VirtualBox ORACLE Deutschland B.V. & Co. KG | Werkstr. 24 | 71384 Weinstadt, Germany Hauptverwaltung: Riesstr. 25, D-80992 München Registergericht: Amtsgericht München, HRA 95603 Geschäftsführer: Jürgen Kunz Komplementärin: ORACLE Deutschland Verwaltung B.V. Hertogswetering 163/167, 3543 AS Utrecht, Niederlande Handelsregister der Handelskammer Midden-Niederlande, Nr. 30143697 Geschäftsführer: Alexander van der Ven, Astrid Kepper, Val Maher
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