G files ports processes belonging to another vm users

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one VM cannot access objects (e.g., files, ports, processes) belonging to another VM. Users have the ability to securely access (remotely log into) VMs created on their behalf. The VM executes a user-provided bootscript each time the VM is started. Users are allowed to install software packages in their VM without consid- eration for the packages installed in other VMs running on the same node. Outgoing network traffic can be audited, such that it is possible to determine time, duration, and flow (source/destination addresses and ports) of all traffic originating from a given VM. To support infrastructure services that require access to private state in an- other VM, it should be possible to grant one VM access to state in another VM. Such access should be granted in adherence to the principle of least privilege. The architecture is somewhat vague on the performance isolation issue because we wish to permit overbooking. A more accurate statement is that it should be possible to completely isolate a VM from the resources consumed by other VMs— i.e., it must be possible to make a resource guarantee to a VM—but not all VMs will take advantage of this option. Among a set of VMs without guarantees, the expectation is that resources are shared fairly. Evolution Note: While VMs are typically implemented by a VMM, it should be possible to allocate an entire physical processor to a VM. In this case, it must be possible to reclaim the processor from one VM and allocate it to another. If we take this broader view of an execution environment, then we should probably return to PlanetLab’s original 10
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terminology of calling the instantiation of a slice on a single node a sliver , but we retain the VM-based nomenclature for the purpose of this document. Each VM is specified (abstractly represented) by a set of attributes , called a resource specification ( RSpec ). An RSpec defines how much of the node’s re- sources are allocated to the VM; it also specifies the VM’s type . PlanetLab cur- rently supports a single Linux-based VMM, and so defines a single VM type ( linux- vserver-x86 ). However, other VM types are possible (e.g., linux-xen-x86 ). In general, the precise execution environment provided by a VM can be de- fined along several dimensions, and hence, the type system for VMs could become arbitrarily complex. This is not a desirable situation, as one of PlanetLab’s most important properties today is that VMs are homogeneous. As our two examples illustrate, we currently define a VM along three dimensions: the operating sys- tem (which roughly defines the available programming interface), the underlying VMM (which indicates whether the user is allowed to install new software in the kernel and mediates how VMs communicate with each other), and the machine architecture (which defines what binaries run in the VM).
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