[Qemu-devel] Re: [PATCH v5 4/5] Inter-VM shared memory PCI device

[Cam Macdonell]

On Mon, May 10, 2010 at 5:59 AM, Avi Kivity <address@hidden> wrote:
> On 04/21/2010 08:53 PM, Cam Macdonell wrote:
>>
>> 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]
>>     -chardev socket,path=<path>,id=<id>
>>
>> (shared memory server is qemu.git/contrib/ivshmem-server)
>>
>> Sample programs and init scripts are in a git repo here:
>>
>>
>> +typedef struct EventfdEntry {
>> +    PCIDevice *pdev;
>> +    int vector;
>> +} EventfdEntry;
>> +
>> +typedef struct IVShmemState {
>> +    PCIDevice dev;
>> +    uint32_t intrmask;
>> +    uint32_t intrstatus;
>> +    uint32_t doorbell;
>> +
>> +    CharDriverState * chr;
>> +    CharDriverState ** eventfd_chr;
>> +    int ivshmem_mmio_io_addr;
>> +
>> +    pcibus_t mmio_addr;
>> +    unsigned long ivshmem_offset;
>> +    uint64_t ivshmem_size; /* size of shared memory region */
>> +    int shm_fd; /* shared memory file descriptor */
>> +
>> +    int nr_allocated_vms;
>> +    /* array of eventfds for each guest */
>> +    int ** eventfds;
>> +    /* keep track of # of eventfds for each guest*/
>> +    int * eventfds_posn_count;
>>
>
> More readable:
>
>  typedef struct Peer {
>      int nb_eventfds;
>      int *eventfds;
>  } Peer;
>  int nb_peers;
>  Peer *peers;
>
> Does eventfd_chr need to be there as well?

No it does not, eventfd_chr store character devices for receiving
interrupts when irqfd is not available, so we only them for this
guest, not for our peers.

I've switched over to this more readable naming you've suggested.

>
>> +
>> +    int nr_alloc_guests;
>> +    int vm_id;
>> +    int num_eventfds;
>> +    uint32_t vectors;
>> +    uint32_t features;
>> +    EventfdEntry *eventfd_table;
>> +
>> +    char * shmobj;
>> +    char * sizearg;
>>
>
> Does this need to be part of the state?

They are because they're passed in as qdev properties from the
command-line so I thought they needed to be in the state struct to be
assigned via DEFINE_PROP_...

>
>> +} 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, int
>> feature) {
>> +    return (ivs->features&  (1<<  feature));
>> +}
>> +
>> +static inline int is_power_of_two(int x) {
>> +    return (x&  (x-1)) == 0;
>> +}
>>
>
> argument needs to be uint64_t to avoid overflow with large BARs.  Return
> type can be bool.
>
>> +static void ivshmem_io_writel(void *opaque, uint8_t addr, uint32_t val)
>> +{
>> +    IVShmemState *s = opaque;
>> +
>> +    u_int64_t write_one = 1;
>> +    u_int16_t dest = val>>  16;
>> +    u_int16_t vector = val&  0xff;
>> +
>> +    addr&= 0xfe;
>>
>
> Why 0xfe?  Can understand 0xfc or 0xff.

Forgot to change to 0xfc when registers went from 16 to 32-bits.

>
>> +
>> +    switch (addr)
>> +    {
>> +        case IntrMask:
>> +            ivshmem_IntrMask_write(s, val);
>> +            break;
>> +
>> +        case IntrStatus:
>> +            ivshmem_IntrStatus_write(s, val);
>> +            break;
>> +
>> +        case Doorbell:
>> +            /* check doorbell range */
>> +            if ((vector>= 0)&&  (vector<  s->eventfds_posn_count[dest]))
>> {
>>
>
> What if dest is too big?  We overflow s->eventfds_posn_count.

added a check for that.

Thanks,
Cam