Memory Overcommit by Using an Emulated IOMMU in a Computer System with a Host IOMMU

A system comprising:

• host memory to store a hypervisor;
• a computer coupled to the host memory to host a plurality of virtual machines and the hypervisor;
• a device coupled to the computer and assigned to a guest operating system of one of the virtual machines, the device to perform direct memory access (DMA) to a buffer managed by the guest operating system;
• and
• a host I/O memory management unit (IOMMU) coupled to the computer,
• wherein the hypervisor, in response to an indication that a bus address is to be used by the device to perform the DMA, determines a host device identifier for the device, pins a memory page addressed by a host address that is associated with the bus address and a guest address to keep the pinned memory page in the host memory, and records in the host IOMMU a mapping of the bus address and the host device identifier to the host address, and wherein the hypervisor removes the mapping after the device completes the DMA.

A computer readable storage medium including instructions that, when executed by a processing system, cause the processing system to perform a method comprising:

• receiving an indication that a bus address is to be used by a device to perform direct memory access (DMA) to a buffer, the buffer being managed by a guest operating system of one of a plurality of virtual machines hosted by a computer;
• determining a host device identifier for the device being assigned to the guest operating system;
• pinning a memory page addressed by a host address that is associated with the bus address and a guest address to keep the pinned memory page in host memory;
• recording, in a host I/O memory management unit (IOMMU), a mapping of the bus address and the host device identifier to the host address;
• and
• removing the mapping after the device completes the DMA.