VMWare PVSCSI Device Interface

This document describes the VMWare PVSCSI device interface specification, based on the source code of the PVSCSI Linux driver from kernel 3.0.4.


The interface is based on a memory area shared between hypervisor and VM. The memory area is obtained by driver as a device IO memory resource of PVSCSI_MEM_SPACE_SIZE length. The shared memory consists of a registers area and a rings area. The registers area is used to raise hypervisor interrupts and issue device commands. The rings area is used to transfer data descriptors and SCSI commands from VM to hypervisor and to transfer messages produced by hypervisor to VM. Data itself is transferred via virtual scatter-gather DMA.

PVSCSI Device Registers

The length of the registers area is 1 page (PVSCSI_MEM_SPACE_COMMAND_NUM_PAGES). The structure of the registers area is described by the PVSCSIRegOffset enum. There are registers to issue device commands (with optional short data), issue device interrupts, and control interrupt masking.

PVSCSI Device Rings

There are three rings in shared memory:

Request ring (struct PVSCSIRingReqDesc *req_ring)

ring for OS to device requests

Completion ring (struct PVSCSIRingCmpDesc *cmp_ring)

ring for device request completions

Message ring (struct PVSCSIRingMsgDesc *msg_ring)

ring for messages from device. This ring is optional and the guest might not configure it.

There is a control area (struct PVSCSIRingsState *rings_state) used to control rings operation.

PVSCSI Device to Host Interrupts

The following interrupt types are supported by the PVSCSI device:

Completion interrupts (completion ring notifications):



Message interrupts (message ring notifications):



Interrupts are controlled via the PVSCSI_REG_OFFSET_INTR_MASK register. If a bit is set it means the interrupt is enabled, and if it is clear then the interrupt is disabled.

The interrupt modes supported are legacy, MSI and MSI-X. In the case of legacy interrupts, the PVSCSI_REG_OFFSET_INTR_STATUS register is used to check which interrupt has arrived. Interrupts are acknowledged when the corresponding bit is written to the interrupt status register.

PVSCSI Device Operation Sequences

Startup sequence


  2. Windows driver reads interrupt status register here

  3. Issue PVSCSI_CMD_SETUP_MSG_RING command with no additional data, check status and disable device messages if error returned (Omitted if device messages disabled by driver configuration)

  4. Issue PVSCSI_CMD_SETUP_RINGS command, provide rings configuration as struct PVSCSICmdDescSetupRings

  5. Issue PVSCSI_CMD_SETUP_MSG_RING command again, provide rings configuration as struct PVSCSICmdDescSetupMsgRing

  6. Unmask completion and message (if device messages enabled) interrupts

Shutdown sequence

  1. Mask interrupts

  2. Flush request ring using PVSCSI_REG_OFFSET_KICK_NON_RW_IO


Send request

  1. Fill next free request ring descriptor

  2. Issue PVSCSI_REG_OFFSET_KICK_RW_IO for R/W operations or PVSCSI_REG_OFFSET_KICK_NON_RW_IO for other operations

Abort command

  1. Issue PVSCSI_CMD_ABORT_CMD command

Request completion processing

  1. Upon completion interrupt arrival process completion and message (if enabled) rings