[Qemu-devel] Re: [PATCH v7 RESEND 4/4] Inter-VM shared memory PCI device

[David S. Ahern]

On 07/08/10 15:08, Cam Macdonell wrote:
> Resent (again): Some lines were over 80 characters and debugging is now off.
> 
> Support an inter-vm shared memory device that maps a shared-memory object as a
> PCI device in the guest.  This patch also supports interrupts between guest by
> communicating over a unix domain socket.  This patch applies to the qemu-kvm
> repository.
> 
>     -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]
> 
> Interrupts are supported between multiple VMs by using a shared memory server
> by using a chardev socket.
> 
>     -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]
>            [,chardev=<id>][,msi=on][,irqfd=on][,vectors=n][,role=peer|master]
>     -chardev socket,path=<path>,id=<id>
> 
> The shared memory server, sample programs and init scripts are in a git repo 
> here:
> 
>     www.gitorious.org/nahanni
> 

This is an oft requested feature that Cam's been working on for a while
now. I've tested the plan host-VM shared memory aspect and it works
quite nicely. Can this get committed soon?

David


> Signed-off-by: Cam Macdonell <address@hidden>
> ---
>  Makefile.target |    3 +
>  hw/ivshmem.c    |  842 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  qemu-char.c     |    6 +
>  qemu-char.h     |    3 +
>  qemu-doc.texi   |   43 +++
>  5 files changed, 897 insertions(+), 0 deletions(-)
>  create mode 100644 hw/ivshmem.c
> 
> diff --git a/Makefile.target b/Makefile.target
> index a0e9747..1e99ec8 100644
> --- a/Makefile.target
> +++ b/Makefile.target
> @@ -203,6 +203,9 @@ obj-$(CONFIG_USB_OHCI) += usb-ohci.o
>  obj-y += rtl8139.o
>  obj-y += e1000.o
>  
> +# Inter-VM PCI shared memory
> +obj-y += ivshmem.o
> +
>  # Hardware support
>  obj-i386-y += vga.o
>  obj-i386-y += mc146818rtc.o i8259.o pc.o
> diff --git a/hw/ivshmem.c b/hw/ivshmem.c
> new file mode 100644
> index 0000000..763b9c2
> --- /dev/null
> +++ b/hw/ivshmem.c
> @@ -0,0 +1,842 @@
> +/*
> + * Inter-VM Shared Memory PCI device.
> + *
> + * Author:
> + *      Cam Macdonell <address@hidden>
> + *
> + * Based On: cirrus_vga.c
> + *          Copyright (c) 2004 Fabrice Bellard
> + *          Copyright (c) 2004 Makoto Suzuki (suzu)
> + *
> + *      and rtl8139.c
> + *          Copyright (c) 2006 Igor Kovalenko
> + *
> + * This code is licensed under the GNU GPL v2.
> + */
> +#include "hw.h"
> +#include "pc.h"
> +#include "pci.h"
> +#include "msix.h"
> +#include "kvm.h"
> +
> +#include <sys/mman.h>
> +#include <sys/types.h>
> +
> +#define IVSHMEM_IRQFD   0
> +#define IVSHMEM_MSI     1
> +
> +#define IVSHMEM_PEER    0
> +#define IVSHMEM_MASTER  1
> +
> +#define IVSHMEM_REG_BAR_SIZE 0x100
> +
> +//#define DEBUG_IVSHMEM
> +#ifdef DEBUG_IVSHMEM
> +#define IVSHMEM_DPRINTF(fmt, ...)        \
> +    do {printf("IVSHMEM: " fmt, ## __VA_ARGS__); } while (0)
> +#else
> +#define IVSHMEM_DPRINTF(fmt, ...)
> +#endif
> +
> +typedef struct Peer {
> +    int nb_eventfds;
> +    int *eventfds;
> +} Peer;
> +
> +typedef struct EventfdEntry {
> +    PCIDevice *pdev;
> +    int vector;
> +} EventfdEntry;
> +
> +typedef struct IVShmemState {
> +    PCIDevice dev;
> +    uint32_t intrmask;
> +    uint32_t intrstatus;
> +    uint32_t doorbell;
> +
> +    CharDriverState **eventfd_chr;
> +    CharDriverState *server_chr;
> +    int ivshmem_mmio_io_addr;
> +
> +    pcibus_t mmio_addr;
> +    pcibus_t shm_pci_addr;
> +    uint64_t ivshmem_offset;
> +    uint64_t ivshmem_size; /* size of shared memory region */
> +    int shm_fd; /* shared memory file descriptor */
> +
> +    Peer *peers;
> +    int nb_peers; /* how many guests we have space for */
> +    int max_peer; /* maximum numbered peer */
> +
> +    int vm_id;
> +    uint32_t vectors;
> +    uint32_t features;
> +    EventfdEntry *eventfd_table;
> +
> +    char * shmobj;
> +    char * sizearg;
> +    char * role;
> +    int role_val;   /* scalar to avoid multiple string comparisons */
> +} IVShmemState;
> +
> +/* registers for the Inter-VM shared memory device */
> +enum ivshmem_registers {
> +    INTRMASK = 0,
> +    INTRSTATUS = 4,
> +    IVPOSITION = 8,
> +    DOORBELL = 12,
> +};
> +
> +static inline uint32_t ivshmem_has_feature(IVShmemState *ivs,
> +                                                    unsigned int feature) {
> +    return (ivs->features & (1 << feature));
> +}
> +
> +static inline bool is_power_of_two(uint64_t x) {
> +    return (x & (x - 1)) == 0;
> +}
> +
> +static void ivshmem_map(PCIDevice *pci_dev, int region_num,
> +                    pcibus_t addr, pcibus_t size, int type)
> +{
> +    IVShmemState *s = DO_UPCAST(IVShmemState, dev, pci_dev);
> +
> +    s->shm_pci_addr = addr;
> +
> +    if (s->ivshmem_offset > 0) {
> +        cpu_register_physical_memory(s->shm_pci_addr, s->ivshmem_size,
> +                                                            
> s->ivshmem_offset);
> +    }
> +
> +    IVSHMEM_DPRINTF("guest pci addr = %" FMT_PCIBUS ", guest h/w addr = %"
> +        PRIu64 ", size = %" FMT_PCIBUS "\n", addr, s->ivshmem_offset, size);
> +
> +}
> +
> +/* accessing registers - based on rtl8139 */
> +static void ivshmem_update_irq(IVShmemState *s, int val)
> +{
> +    int isr;
> +    isr = (s->intrstatus & s->intrmask) & 0xffffffff;
> +
> +    /* don't print ISR resets */
> +    if (isr) {
> +        IVSHMEM_DPRINTF("Set IRQ to %d (%04x %04x)\n",
> +           isr ? 1 : 0, s->intrstatus, s->intrmask);
> +    }
> +
> +    qemu_set_irq(s->dev.irq[0], (isr != 0));
> +}
> +
> +static void ivshmem_IntrMask_write(IVShmemState *s, uint32_t val)
> +{
> +    IVSHMEM_DPRINTF("IntrMask write(w) val = 0x%04x\n", val);
> +
> +    s->intrmask = val;
> +
> +    ivshmem_update_irq(s, val);
> +}
> +
> +static uint32_t ivshmem_IntrMask_read(IVShmemState *s)
> +{
> +    uint32_t ret = s->intrmask;
> +
> +    IVSHMEM_DPRINTF("intrmask read(w) val = 0x%04x\n", ret);
> +
> +    return ret;
> +}
> +
> +static void ivshmem_IntrStatus_write(IVShmemState *s, uint32_t val)
> +{
> +    IVSHMEM_DPRINTF("IntrStatus write(w) val = 0x%04x\n", val);
> +
> +    s->intrstatus = val;
> +
> +    ivshmem_update_irq(s, val);
> +    return;
> +}
> +
> +static uint32_t ivshmem_IntrStatus_read(IVShmemState *s)
> +{
> +    uint32_t ret = s->intrstatus;
> +
> +    /* reading ISR clears all interrupts */
> +    s->intrstatus = 0;
> +
> +    ivshmem_update_irq(s, 0);
> +
> +    return ret;
> +}
> +
> +static void ivshmem_io_writew(void *opaque, target_phys_addr_t addr,
> +                                                            uint32_t val)
> +{
> +
> +    IVSHMEM_DPRINTF("We shouldn't be writing words\n");
> +}
> +
> +static void ivshmem_io_writel(void *opaque, target_phys_addr_t addr,
> +                                                            uint32_t val)
> +{
> +    IVShmemState *s = opaque;
> +
> +    uint64_t write_one = 1;
> +    uint16_t dest = val >> 16;
> +    uint16_t vector = val & 0xff;
> +
> +    addr &= 0xfc;
> +
> +    IVSHMEM_DPRINTF("writing to addr " TARGET_FMT_plx "\n", addr);
> +    switch (addr)
> +    {
> +        case INTRMASK:
> +            ivshmem_IntrMask_write(s, val);
> +            break;
> +
> +        case INTRSTATUS:
> +            ivshmem_IntrStatus_write(s, val);
> +            break;
> +
> +        case DOORBELL:
> +            /* check that dest VM ID is reasonable */
> +            if ((dest < 0) || (dest > s->max_peer)) {
> +                IVSHMEM_DPRINTF("Invalid destination VM ID (%d)\n", dest);
> +                break;
> +            }
> +
> +            /* check doorbell range */
> +            if ((vector >= 0) && (vector < s->peers[dest].nb_eventfds)) {
> +                IVSHMEM_DPRINTF("Writing %" PRId64 " to VM %d on vector 
> %d\n",
> +                                                    write_one, dest, vector);
> +                if (write(s->peers[dest].eventfds[vector],
> +                                                    &(write_one), 8) != 8) {
> +                    IVSHMEM_DPRINTF("error writing to eventfd\n");
> +                }
> +            }
> +            break;
> +        default:
> +            IVSHMEM_DPRINTF("Invalid VM Doorbell VM %d\n", dest);
> +    }
> +}
> +
> +static void ivshmem_io_writeb(void *opaque, target_phys_addr_t addr,
> +                                                                uint32_t val)
> +{
> +    IVSHMEM_DPRINTF("We shouldn't be writing bytes\n");
> +}
> +
> +static uint32_t ivshmem_io_readw(void *opaque, target_phys_addr_t addr)
> +{
> +
> +    IVSHMEM_DPRINTF("We shouldn't be reading words\n");
> +    return 0;
> +}
> +
> +static uint32_t ivshmem_io_readl(void *opaque, target_phys_addr_t addr)
> +{
> +
> +    IVShmemState *s = opaque;
> +    uint32_t ret;
> +
> +    switch (addr)
> +    {
> +        case INTRMASK:
> +            ret = ivshmem_IntrMask_read(s);
> +            break;
> +
> +        case INTRSTATUS:
> +            ret = ivshmem_IntrStatus_read(s);
> +            break;
> +
> +        case IVPOSITION:
> +            /* return my VM ID if the memory is mapped */
> +            if (s->shm_fd > 0) {
> +                ret = s->vm_id;
> +            } else {
> +                ret = -1;
> +            }
> +            break;
> +
> +        default:
> +            IVSHMEM_DPRINTF("why are we reading " TARGET_FMT_plx "\n", addr);
> +            ret = 0;
> +    }
> +
> +    return ret;
> +}
> +
> +static uint32_t ivshmem_io_readb(void *opaque, target_phys_addr_t addr)
> +{
> +    IVSHMEM_DPRINTF("We shouldn't be reading bytes\n");
> +
> +    return 0;
> +}
> +
> +static CPUReadMemoryFunc * const ivshmem_mmio_read[3] = {
> +    ivshmem_io_readb,
> +    ivshmem_io_readw,
> +    ivshmem_io_readl,
> +};
> +
> +static CPUWriteMemoryFunc * const ivshmem_mmio_write[3] = {
> +    ivshmem_io_writeb,
> +    ivshmem_io_writew,
> +    ivshmem_io_writel,
> +};
> +
> +static void ivshmem_receive(void *opaque, const uint8_t *buf, int size)
> +{
> +    IVShmemState *s = opaque;
> +
> +    ivshmem_IntrStatus_write(s, *buf);
> +
> +    IVSHMEM_DPRINTF("ivshmem_receive 0x%02x\n", *buf);
> +}
> +
> +static int ivshmem_can_receive(void * opaque)
> +{
> +    return 8;
> +}
> +
> +static void ivshmem_event(void *opaque, int event)
> +{
> +    IVSHMEM_DPRINTF("ivshmem_event %d\n", event);
> +}
> +
> +static void fake_irqfd(void *opaque, const uint8_t *buf, int size) {
> +
> +    EventfdEntry *entry = opaque;
> +    PCIDevice *pdev = entry->pdev;
> +
> +    IVSHMEM_DPRINTF("fake irqfd on vector %p %d\n", pdev, entry->vector);
> +    msix_notify(pdev, entry->vector);
> +}
> +
> +static CharDriverState* create_eventfd_chr_device(void * opaque, int eventfd,
> +                                                                    int 
> vector)
> +{
> +    /* create a event character device based on the passed eventfd */
> +    IVShmemState *s = opaque;
> +    CharDriverState * chr;
> +
> +    chr = qemu_chr_open_eventfd(eventfd);
> +
> +    if (chr == NULL) {
> +        fprintf(stderr, "creating eventfd for eventfd %d failed\n", eventfd);
> +        exit(-1);
> +    }
> +
> +    /* if MSI is supported we need multiple interrupts */
> +    if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
> +        s->eventfd_table[vector].pdev = &s->dev;
> +        s->eventfd_table[vector].vector = vector;
> +
> +        qemu_chr_add_handlers(chr, ivshmem_can_receive, fake_irqfd,
> +                      ivshmem_event, &s->eventfd_table[vector]);
> +    } else {
> +        qemu_chr_add_handlers(chr, ivshmem_can_receive, ivshmem_receive,
> +                      ivshmem_event, s);
> +    }
> +
> +    return chr;
> +
> +}
> +
> +static int check_shm_size(IVShmemState *s, int fd) {
> +    /* check that the guest isn't going to try and map more memory than the
> +     * the object has allocated return -1 to indicate error */
> +
> +    struct stat buf;
> +
> +    fstat(fd, &buf);
> +
> +    if (s->ivshmem_size > buf.st_size) {
> +        fprintf(stderr, "IVSHMEM ERROR: Requested memory size greater");
> +        fprintf(stderr, " than shared object size (%" PRIu64 " > %ld)\n",
> +                                          s->ivshmem_size, buf.st_size);
> +        return -1;
> +    } else {
> +        return 0;
> +    }
> +}
> +
> +/* create the shared memory BAR when we are not using the server, so we can
> + * create the BAR and map the memory immediately */
> +static void create_shared_memory_BAR(IVShmemState *s, int fd) {
> +
> +    void * ptr;
> +
> +    s->shm_fd = fd;
> +
> +    ptr = mmap(0, s->ivshmem_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
> +
> +    s->ivshmem_offset = qemu_ram_map(s->ivshmem_size, ptr);
> +
> +    /* region for shared memory */
> +    pci_register_bar(&s->dev, 2, s->ivshmem_size,
> +                                PCI_BASE_ADDRESS_SPACE_MEMORY, ivshmem_map);
> +}
> +
> +static void close_guest_eventfds(IVShmemState *s, int posn)
> +{
> +    int i, guest_curr_max;
> +
> +    guest_curr_max = s->peers[posn].nb_eventfds;
> +
> +    for (i = 0; i < guest_curr_max; i++) {
> +        kvm_set_ioeventfd_mmio_long(s->peers[posn].eventfds[i],
> +                    s->mmio_addr + DOORBELL, (posn << 16) | i, 0);
> +        close(s->peers[posn].eventfds[i]);
> +    }
> +
> +    qemu_free(s->peers[posn].eventfds);
> +    s->peers[posn].nb_eventfds = 0;
> +}
> +
> +static void setup_ioeventfds(IVShmemState *s) {
> +
> +    int i, j;
> +
> +    for (i = 0; i <= s->max_peer; i++) {
> +        for (j = 0; j < s->peers[i].nb_eventfds; j++) {
> +            kvm_set_ioeventfd_mmio_long(s->peers[i].eventfds[j],
> +                    s->mmio_addr + DOORBELL, (i << 16) | j, 1);
> +        }
> +    }
> +
> +#ifdef CONFIG_KVM
> +    /* setup irqfd for this VM's eventfds */
> +    for (i = 0; i < s->vectors; i++) {
> +        kvm_set_irqfd(s->dev.msix_irq_entries[i].gsi,
> +                        s->peers[s->vm_id].eventfds[i], 1);
> +    }
> +#endif
> +}
> +
> +
> +/* this function increase the dynamic storage need to store data about other
> + * guests */
> +static void increase_dynamic_storage(IVShmemState *s, int new_min_size) {
> +
> +    int j, old_nb_alloc;
> +
> +    old_nb_alloc = s->nb_peers;
> +
> +    while (new_min_size >= s->nb_peers)
> +        s->nb_peers = s->nb_peers * 2;
> +
> +    IVSHMEM_DPRINTF("bumping storage to %d guests\n", s->nb_peers);
> +    s->peers = qemu_realloc(s->peers, s->nb_peers * sizeof(Peer));
> +
> +    /* zero out new pointers */
> +    for (j = old_nb_alloc; j < s->nb_peers; j++) {
> +        s->peers[j].eventfds = NULL;
> +        s->peers[j].nb_eventfds = 0;
> +    }
> +}
> +
> +static void ivshmem_read(void *opaque, const uint8_t * buf, int flags)
> +{
> +    IVShmemState *s = opaque;
> +    int incoming_fd, tmp_fd;
> +    int guest_max_eventfd;
> +    long incoming_posn;
> +
> +    memcpy(&incoming_posn, buf, sizeof(long));
> +    /* pick off s->server_chr->msgfd and store it, posn should accompany msg 
> */
> +    tmp_fd = qemu_chr_get_msgfd(s->server_chr);
> +    IVSHMEM_DPRINTF("posn is %ld, fd is %d\n", incoming_posn, tmp_fd);
> +
> +    /* make sure we have enough space for this guest */
> +    if (incoming_posn >= s->nb_peers) {
> +        increase_dynamic_storage(s, incoming_posn);
> +    }
> +
> +    if (tmp_fd == -1) {
> +        /* if posn is positive and unseen before then this is our posn*/
> +        if ((incoming_posn >= 0) &&
> +                            (s->peers[incoming_posn].eventfds == NULL)) {
> +            /* receive our posn */
> +            s->vm_id = incoming_posn;
> +            return;
> +        } else {
> +            /* otherwise an fd == -1 means an existing guest has gone away */
> +            IVSHMEM_DPRINTF("posn %ld has gone away\n", incoming_posn);
> +            close_guest_eventfds(s, incoming_posn);
> +            return;
> +        }
> +    }
> +
> +    /* because of the implementation of get_msgfd, we need a dup */
> +    incoming_fd = dup(tmp_fd);
> +
> +    if (incoming_fd == -1) {
> +        fprintf(stderr, "could not allocate file descriptor %s\n",
> +                                                            strerror(errno));
> +        return;
> +    }
> +
> +    /* if the position is -1, then it's shared memory region fd */
> +    if (incoming_posn == -1) {
> +
> +        void * map_ptr;
> +
> +        s->max_peer = 0;
> +
> +        if (check_shm_size(s, incoming_fd) == -1) {
> +            exit(-1);
> +        }
> +
> +        /* mmap the region and map into the BAR2 */
> +        map_ptr = mmap(0, s->ivshmem_size, PROT_READ|PROT_WRITE, MAP_SHARED,
> +                                                            incoming_fd, 0);
> +        s->ivshmem_offset = qemu_ram_map(s->ivshmem_size, map_ptr);
> +
> +        IVSHMEM_DPRINTF("guest pci addr = %" FMT_PCIBUS ", guest h/w addr = 
> %"
> +                         PRIu64 ", size = %" PRIu64 "\n", s->shm_pci_addr,
> +                         s->ivshmem_offset, s->ivshmem_size);
> +
> +        if (s->shm_pci_addr > 0) {
> +            /* map memory into BAR2 */
> +            cpu_register_physical_memory(s->shm_pci_addr, s->ivshmem_size,
> +                                                            
> s->ivshmem_offset);
> +        }
> +
> +        /* only store the fd if it is successfully mapped */
> +        s->shm_fd = incoming_fd;
> +
> +        return;
> +    }
> +
> +    /* each guest has an array of eventfds, and we keep track of how many
> +     * guests for each VM */
> +    guest_max_eventfd = s->peers[incoming_posn].nb_eventfds;
> +
> +    if (guest_max_eventfd == 0) {
> +        /* one eventfd per MSI vector */
> +        s->peers[incoming_posn].eventfds = (int *) qemu_malloc(s->vectors *
> +                                                                sizeof(int));
> +    }
> +
> +    /* this is an eventfd for a particular guest VM */
> +    IVSHMEM_DPRINTF("eventfds[%ld][%d] = %d\n", incoming_posn,
> +                                            guest_max_eventfd, incoming_fd);
> +    s->peers[incoming_posn].eventfds[guest_max_eventfd] = incoming_fd;
> +
> +    /* increment count for particular guest */
> +    s->peers[incoming_posn].nb_eventfds++;
> +
> +    /* keep track of the maximum VM ID */
> +    if (incoming_posn > s->max_peer) {
> +        s->max_peer = incoming_posn;
> +    }
> +
> +    if (incoming_posn == s->vm_id) {
> +        if (!ivshmem_has_feature(s, IVSHMEM_IRQFD)) {
> +            /* initialize char device for callback
> +             * if this is one of my eventfds */
> +            s->eventfd_chr[guest_max_eventfd] = create_eventfd_chr_device(s,
> +                       s->peers[s->vm_id].eventfds[guest_max_eventfd],
> +                       guest_max_eventfd);
> +        }
> +    }
> +
> +    if (ivshmem_has_feature(s, IVSHMEM_IRQFD)) {
> +        kvm_set_ioeventfd_mmio_long(incoming_fd, s->mmio_addr + DOORBELL,
> +                                (incoming_posn << 16) | guest_max_eventfd, 
> 1);
> +    }
> +
> +    return;
> +}
> +
> +static void ivshmem_reset(DeviceState *d)
> +{
> +    IVShmemState *s = DO_UPCAST(IVShmemState, dev.qdev, d);
> +
> +    s->intrstatus = 0;
> +    return;
> +}
> +
> +static void ivshmem_mmio_map(PCIDevice *pci_dev, int region_num,
> +                       pcibus_t addr, pcibus_t size, int type)
> +{
> +    IVShmemState *s = DO_UPCAST(IVShmemState, dev, pci_dev);
> +
> +    s->mmio_addr = addr;
> +    cpu_register_physical_memory(addr + 0, IVSHMEM_REG_BAR_SIZE,
> +                                                s->ivshmem_mmio_io_addr);
> +
> +    /* ioeventfd and irqfd are enabled together,
> +     * so the flag IRQFD refers to both */
> +    if (ivshmem_has_feature(s, IVSHMEM_IRQFD)) {
> +        setup_ioeventfds(s);
> +    }
> +}
> +
> +static uint64_t ivshmem_get_size(IVShmemState * s) {
> +
> +    uint64_t value;
> +    char *ptr;
> +
> +    value = strtoull(s->sizearg, &ptr, 10);
> +    switch (*ptr) {
> +        case 0: case 'M': case 'm':
> +            value <<= 20;
> +            break;
> +        case 'G': case 'g':
> +            value <<= 30;
> +            break;
> +        default:
> +            fprintf(stderr, "qemu: invalid ram size: %s\n", s->sizearg);
> +            exit(1);
> +    }
> +
> +    /* BARs must be a power of 2 */
> +    if (!is_power_of_two(value)) {
> +        fprintf(stderr, "ivshmem: size must be power of 2\n");
> +        exit(1);
> +    }
> +
> +    return value;
> +}
> +
> +static void ivshmem_setup_msi(IVShmemState * s) {
> +
> +    int i;
> +
> +    /* allocate the MSI-X vectors */
> +
> +    if (!msix_init(&s->dev, s->vectors, 1, 0)) {
> +        pci_register_bar(&s->dev, 1,
> +                         msix_bar_size(&s->dev),
> +                         PCI_BASE_ADDRESS_SPACE_MEMORY,
> +                         msix_mmio_map);
> +        IVSHMEM_DPRINTF("msix initialized (%d vectors)\n", s->vectors);
> +    } else {
> +        IVSHMEM_DPRINTF("msix initialization failed\n");
> +        exit(1);
> +    }
> +
> +    /* 'activate' the vectors */
> +    for (i = 0; i < s->vectors; i++) {
> +        msix_vector_use(&s->dev, i);
> +    }
> +
> +    /* if IRQFDs are not supported, we'll have to trigger the interrupts
> +     * via Qemu char devices */
> +    if (!ivshmem_has_feature(s, IVSHMEM_IRQFD)) {
> +        /* for handling interrupts when IRQFD is not available */
> +        s->eventfd_table = qemu_mallocz(s->vectors * sizeof(EventfdEntry));
> +    }
> +}
> +
> +static void ivshmem_save(QEMUFile* f, void *opaque)
> +{
> +    IVShmemState *proxy = opaque;
> +
> +    IVSHMEM_DPRINTF("ivshmem_save\n");
> +    pci_device_save(&proxy->dev, f);
> +
> +    if (ivshmem_has_feature(proxy, IVSHMEM_MSI)) {
> +        msix_save(&proxy->dev, f);
> +    } else {
> +        qemu_put_be32(f, proxy->intrstatus);
> +        qemu_put_be32(f, proxy->intrmask);
> +    }
> +
> +}
> +
> +static int ivshmem_load(QEMUFile* f, void *opaque, int version_id)
> +{
> +    IVSHMEM_DPRINTF("ivshmem_load\n");
> +
> +    IVShmemState *proxy = opaque;
> +    int ret, i;
> +
> +    if (version_id > 0) {
> +        return -EINVAL;
> +    }
> +
> +    if (proxy->role_val == IVSHMEM_PEER) {
> +        fprintf(stderr, "ivshmem: 'peer' devices are not migratable\n");
> +        return -EINVAL;
> +    }
> +
> +    ret = pci_device_load(&proxy->dev, f);
> +    if (ret) {
> +        return ret;
> +    }
> +
> +    if (ivshmem_has_feature(proxy, IVSHMEM_MSI)) {
> +        msix_load(&proxy->dev, f);
> +        for (i = 0; i < proxy->vectors; i++) {
> +            msix_vector_use(&proxy->dev, i);
> +        }
> +    } else {
> +        proxy->intrstatus = qemu_get_be32(f);
> +        proxy->intrmask = qemu_get_be32(f);
> +    }
> +
> +    return 0;
> +}
> +
> +static int pci_ivshmem_init(PCIDevice *dev)
> +{
> +    IVShmemState *s = DO_UPCAST(IVShmemState, dev, dev);
> +    uint8_t *pci_conf;
> +
> +    if (s->sizearg == NULL)
> +        s->ivshmem_size = 4 << 20; /* 4 MB default */
> +    else {
> +        s->ivshmem_size = ivshmem_get_size(s);
> +    }
> +
> +    register_savevm("ivshmem", 0, 0, ivshmem_save, ivshmem_load, dev);
> +
> +    /* IRQFD requires MSI */
> +    if (ivshmem_has_feature(s, IVSHMEM_IRQFD) &&
> +        !ivshmem_has_feature(s, IVSHMEM_MSI)) {
> +        fprintf(stderr, "ivshmem: ioeventfd/irqfd requires MSI\n");
> +        exit(1);
> +    }
> +
> +    /* check that role is reasonable */
> +    if (s->role) {
> +        if (strncmp(s->role, "peer", 5) == 0) {
> +            s->role_val = IVSHMEM_PEER;
> +        } else if (strncmp(s->role, "master", 7) == 0) {
> +            s->role_val = IVSHMEM_MASTER;
> +        } else {
> +            fprintf(stderr, "ivshmem: 'role' must be 'peer' or 'master'\n");
> +            exit(1);
> +        }
> +    } else {
> +        s->role_val = IVSHMEM_MASTER; /* default */
> +    }
> +
> +    if (s->role_val == IVSHMEM_PEER) {
> +        register_device_unmigratable("ivshmem", s);
> +    }
> +
> +    pci_conf = s->dev.config;
> +    pci_config_set_vendor_id(pci_conf, PCI_VENDOR_ID_REDHAT_QUMRANET);
> +    pci_conf[0x02] = 0x10;
> +    pci_conf[0x03] = 0x11;
> +    pci_conf[PCI_COMMAND] = PCI_COMMAND_IO | PCI_COMMAND_MEMORY;
> +    pci_config_set_class(pci_conf, PCI_CLASS_MEMORY_RAM);
> +    pci_conf[PCI_HEADER_TYPE] = PCI_HEADER_TYPE_NORMAL;
> +
> +    pci_config_set_interrupt_pin(pci_conf, 1);
> +
> +    s->shm_pci_addr = 0;
> +    s->ivshmem_offset = 0;
> +    s->shm_fd = 0;
> +
> +    s->ivshmem_mmio_io_addr = cpu_register_io_memory(ivshmem_mmio_read,
> +                                    ivshmem_mmio_write, s);
> +    /* region for registers*/
> +    pci_register_bar(&s->dev, 0, IVSHMEM_REG_BAR_SIZE,
> +                           PCI_BASE_ADDRESS_SPACE_MEMORY, ivshmem_mmio_map);
> +
> +    if ((s->server_chr != NULL) &&
> +                        (strncmp(s->server_chr->filename, "unix:", 5) == 0)) 
> {
> +        /* if we get a UNIX socket as the parameter we will talk
> +         * to the ivshmem server to receive the memory region */
> +
> +        if (s->shmobj != NULL) {
> +            fprintf(stderr, "WARNING: do not specify both 'chardev' "
> +                                                "and 'shm' with ivshmem\n");
> +        }
> +
> +        IVSHMEM_DPRINTF("using shared memory server (socket = %s)\n",
> +                                                    s->server_chr->filename);
> +
> +        if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
> +            ivshmem_setup_msi(s);
> +        }
> +
> +        /* we allocate enough space for 16 guests and grow as needed */
> +        s->nb_peers = 16;
> +        s->vm_id = -1;
> +
> +        /* allocate/initialize space for interrupt handling */
> +        s->peers = qemu_mallocz(s->nb_peers * sizeof(Peer));
> +
> +        pci_register_bar(&s->dev, 2, s->ivshmem_size,
> +                                PCI_BASE_ADDRESS_SPACE_MEMORY, ivshmem_map);
> +
> +        s->eventfd_chr = qemu_mallocz(s->vectors * sizeof(CharDriverState 
> *));
> +
> +        qemu_chr_add_handlers(s->server_chr, ivshmem_can_receive, 
> ivshmem_read,
> +                     ivshmem_event, s);
> +    } else {
> +        /* just map the file immediately, we're not using a server */
> +        int fd;
> +
> +        if (s->shmobj == NULL) {
> +            fprintf(stderr, "Must specify 'chardev' or 'shm' to ivshmem\n");
> +        }
> +
> +        IVSHMEM_DPRINTF("using shm_open (shm object = %s)\n", s->shmobj);
> +
> +        /* try opening with O_EXCL and if it succeeds zero the memory
> +         * by truncating to 0 */
> +        if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR|O_EXCL,
> +                        S_IRWXU|S_IRWXG|S_IRWXO)) > 0) {
> +           /* truncate file to length PCI device's memory */
> +            if (ftruncate(fd, s->ivshmem_size) != 0) {
> +                fprintf(stderr, "ivshmem: could not truncate shared file\n");
> +            }
> +
> +        } else if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR,
> +                        S_IRWXU|S_IRWXG|S_IRWXO)) < 0) {
> +            fprintf(stderr, "ivshmem: could not open shared file\n");
> +            exit(-1);
> +
> +        }
> +
> +        if (check_shm_size(s, fd) == -1) {
> +            exit(-1);
> +        }
> +
> +        create_shared_memory_BAR(s, fd);
> +
> +    }
> +
> +    return 0;
> +}
> +
> +static int pci_ivshmem_uninit(PCIDevice *dev)
> +{
> +    IVShmemState *s = DO_UPCAST(IVShmemState, dev, dev);
> +
> +    cpu_unregister_io_memory(s->ivshmem_mmio_io_addr);
> +    unregister_savevm("ivshmem", s);
> +
> +    return 0;
> +}
> +
> +static PCIDeviceInfo ivshmem_info = {
> +    .qdev.name  = "ivshmem",
> +    .qdev.size  = sizeof(IVShmemState),
> +    .qdev.reset = ivshmem_reset,
> +    .init       = pci_ivshmem_init,
> +    .exit       = pci_ivshmem_uninit,
> +    .qdev.props = (Property[]) {
> +        DEFINE_PROP_CHR("chardev", IVShmemState, server_chr),
> +        DEFINE_PROP_STRING("size", IVShmemState, sizearg),
> +        DEFINE_PROP_UINT32("vectors", IVShmemState, vectors, 1),
> +        DEFINE_PROP_BIT("irqfd", IVShmemState, features, IVSHMEM_IRQFD, 
> false),
> +        DEFINE_PROP_BIT("msi", IVShmemState, features, IVSHMEM_MSI, true),
> +        DEFINE_PROP_STRING("shm", IVShmemState, shmobj),
> +        DEFINE_PROP_STRING("role", IVShmemState, role),
> +        DEFINE_PROP_END_OF_LIST(),
> +    }
> +};
> +
> +static void ivshmem_register_devices(void)
> +{
> +    pci_qdev_register(&ivshmem_info);
> +}
> +
> +device_init(ivshmem_register_devices)
> diff --git a/qemu-char.c b/qemu-char.c
> index faaf624..65eaf3b 100644
> --- a/qemu-char.c
> +++ b/qemu-char.c
> @@ -2093,6 +2093,12 @@ static void tcp_chr_read(void *opaque)
>      }
>  }
>  
> +CharDriverState *qemu_chr_open_eventfd(int eventfd){
> +
> +    return qemu_chr_open_fd(eventfd, eventfd);
> +
> +}
> +
>  static void tcp_chr_connect(void *opaque)
>  {
>      CharDriverState *chr = opaque;
> diff --git a/qemu-char.h b/qemu-char.h
> index e3a0783..6ea01ba 100644
> --- a/qemu-char.h
> +++ b/qemu-char.h
> @@ -94,6 +94,9 @@ void qemu_chr_info_print(Monitor *mon, const QObject 
> *ret_data);
>  void qemu_chr_info(Monitor *mon, QObject **ret_data);
>  CharDriverState *qemu_chr_find(const char *name);
>  
> +/* add an eventfd to the qemu devices that are polled */
> +CharDriverState *qemu_chr_open_eventfd(int eventfd);
> +
>  extern int term_escape_char;
>  
>  /* async I/O support */
> diff --git a/qemu-doc.texi b/qemu-doc.texi
> index e2c8e56..67ec244 100644
> --- a/qemu-doc.texi
> +++ b/qemu-doc.texi
> @@ -706,6 +706,49 @@ Using the @option{-net socket} option, it is possible to 
> make VLANs
>  that span several QEMU instances. See @ref{sec_invocation} to have a
>  basic example.
>  
> address@hidden Other Devices
> +
> address@hidden Inter-VM Shared Memory device
> +
> +With KVM enabled on a Linux host, a shared memory device is available.  
> Guests
> +map a POSIX shared memory region into the guest as a PCI device that enables
> +zero-copy communication to the application level of the guests.  The basic
> +syntax is:
> +
> address@hidden
> +qemu -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]
> address@hidden example
> +
> +If desired, interrupts can be sent between guest VMs accessing the same 
> shared
> +memory region.  Interrupt support requires using a shared memory server and
> +using a chardev socket to connect to it.  The code for the shared memory 
> server
> +is qemu.git/contrib/ivshmem-server.  An example syntax when using the shared
> +memory server is:
> +
> address@hidden
> +qemu -device ivshmem,size=<size in format accepted by -m>[,chardev=<id>]
> +                        [,msi=on][,irqfd=on][,vectors=n][,role=peer|master]
> +qemu -chardev socket,path=<path>,id=<id>
> address@hidden example
> +
> +When using the server, the guest will be assigned a VM ID (>=0) that allows 
> guests
> +using the same server to communicate via interrupts.  Guests can read their
> +VM ID from a device register (see example code).  Since receiving the shared
> +memory region from the server is asynchronous, there is a (small) chance the
> +guest may boot before the shared memory is attached.  To allow an application
> +to ensure shared memory is attached, the VM ID register will return -1 (an
> +invalid VM ID) until the memory is attached.  Once the shared memory is
> +attached, the VM ID will return the guest's valid VM ID.  With these 
> semantics,
> +the guest application can check to ensure the shared memory is attached to 
> the
> +guest before proceeding.
> +
> +The @option{role} argument can be set to either master or peer and will 
> affect
> +how the shared memory is migrated.  With @option{role=master}, the guest will
> +copy the shared memory on migration to the destination host.  With
> address@hidden, the guest will not be able to migrate with the device 
> attached.
> +With the @option{peer} case, the device should be detached and then 
> reattached
> +after migration using the PCI hotplug support.
> +
>  @node direct_linux_boot
>  @section Direct Linux Boot
>