A mobile system with a runtime environment supporting virtual machines, the mobile system comprising: a host with a physical memory and a physical address space, a central processing unit, CPU, a graphics-processing unit, GPU, with a GPU server, a stub driver, a frame buffer, a display controller, and a screen, the CPU, GPU and display controller sharing access to a common physical memory; a frame buffer switch, an input switch, an input driver, a display controller driver, and a policy master keeping the frame buffer switch and the input switch in synchronization; at least one instance of a virtual machine, VM; a plurality of applications running on the virtual machine; a hypervisor supporting the virtual machine; wherein a portion of the physical memory of the host is assigned to each virtual machine; wherein the GPU is paravirtualized for sharing the GPU hardware between the virtual machines; wherein the physical memory of a virtual machine is mapped to the assigned region of the physical memory of the host; wherein the GPU is adapted for providing a trusted path from the virtual machine to the screen, the trusted path being established by the private nature of passing client framebuffers from the virtual machine to the screen, wherein a framebuffer switch maintains a session with each of a number of clients, such that one of these sessions is active in accordance with a respective protection policy, and wherein an input switch passes input events to the active client in accordance with said policy; wherein access to the common physical memory by the CPU and the GPU is mediated by individual memory management units, MMUs; wherein the stub driver communicates with the GPU-server via a communication channel that is controlled by the hypervisor; wherein the GPU server is adapted to construct a page table that maps the GPU address space directly to the physical address space of the host; and wherein the stub driver of a virtual machine being a client forwards every mapping request to the GPU-server, which, in turn, constructs a page table for the virtual machine on the client's behalf. a host with a physical memory and a physical address space, a central processing unit, CPU, a graphics-processing unit, GPU, with a GPU server, a stub driver, a frame buffer, a display controller, and a screen, the CPU, GPU and display controller sharing access to a common physical memory; a frame buffer switch, an input switch, an input driver, a display controller driver, and a policy master keeping the frame buffer switch and the input switch in synchronization; at least one instance of a virtual machine, VM; a plurality of applications running on the virtual machine; a hypervisor supporting the virtual machine; wherein a portion of the physical memory of the host is assigned to each virtual machine; wherein the GPU is paravirtualized for sharing the GPU hardware between the virtual machines; wherein the physical memory of a virtual machine is mapped to the assigned region of the physical memory of the host; wherein the GPU is adapted for providing a trusted path from the virtual machine to the screen, the trusted path being established by the private nature of passing client framebuffers from the virtual machine to the screen, wherein a framebuffer switch maintains a session with each of a number of clients, such that one of these sessions is active in accordance with a respective protection policy, and wherein an input switch passes input events to the active client in accordance with said policy; wherein access to the common physical memory by the CPU and the GPU is mediated by individual memory management units, MMUs; wherein the stub driver communicates with the GPU-server via a communication channel that is controlled by the hypervisor; wherein the GPU server is adapted to construct a page table that maps the GPU address space directly to the physical address space of the host; and wherein the stub driver of a virtual machine being a client forwards every mapping request to the GPU-server, which, in turn, constructs a page table for the virtual machine on the client's behalf.