Re: [dpdk-dev] [PATCH v2 5/7] net/virtio_user: add vhost kernel support

["Tan, Jianfeng" <jianfeng.tan@intel.com>]

Hi Jason,


On 1/9/2017 12:39 PM, Jason Wang wrote:
>
>
> On 2016年12月23日 15:14, Jianfeng Tan wrote:
>> This patch add support vhost kernel as the backend for virtio_user.
>> Three main hook functions are added:
>>    - vhost_kernel_setup() to open char device, each vq pair needs one
>>      vhostfd;
>>    - vhost_kernel_ioctl() to communicate control messages with vhost
>>      kernel module;
>>    - vhost_kernel_enable_queue_pair() to open tap device and set it
>>      as the backend of corresonding vhost fd (that is to say, vq pair).
>>
>> Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
>> ---
>>
[...]
>> +/* TUNSETIFF ifr flags */
>> +#define IFF_TAP          0x0002
>> +#define IFF_NO_PI        0x1000
>> +#define IFF_ONE_QUEUE    0x2000
>> +#define IFF_VNET_HDR     0x4000
>> +#define IFF_MULTI_QUEUE  0x0100
>> +#define IFF_ATTACH_QUEUE 0x0200
>> +#define IFF_DETACH_QUEUE 0x0400
>
> Do we really want to duplicate those things which has been exposed by 
> uapi here?

You mean those defined in <linux/if_tun.h>? Redefine those common 
macros, or include standard header file, with respective pros and cons. 
DPDK prefers the redefinition way as far as I understand, doesn't it?

>
>> +
>> +/* Constants */
>> +#define TUN_DEF_SNDBUF    (1ull << 20)
>> +#define PATH_NET_TUN    "/dev/net/tun"
>> +#define VHOST_KERNEL_MAX_REGIONS    64
>
> Unfortunate not a constant any more since c9ce42f72fd0 vhost: add 
> max_mem_regions module parameter.

Yes, I was considering to ignore this in the initial release. But it's 
not a big effort, I'll try to fix it in latest version.

>
>> +
>> +static uint64_t vhost_req_user_to_kernel[] = {
>> +    [VHOST_USER_SET_OWNER] = VHOST_SET_OWNER,
>> +    [VHOST_USER_RESET_OWNER] = VHOST_RESET_OWNER,
>> +    [VHOST_USER_SET_FEATURES] = VHOST_SET_FEATURES,
>> +    [VHOST_USER_GET_FEATURES] = VHOST_GET_FEATURES,
>> +    [VHOST_USER_SET_VRING_CALL] = VHOST_SET_VRING_CALL,
>> +    [VHOST_USER_SET_VRING_NUM] = VHOST_SET_VRING_NUM,
>> +    [VHOST_USER_SET_VRING_BASE] = VHOST_SET_VRING_BASE,
>> +    [VHOST_USER_GET_VRING_BASE] = VHOST_GET_VRING_BASE,
>> +    [VHOST_USER_SET_VRING_ADDR] = VHOST_SET_VRING_ADDR,
>> +    [VHOST_USER_SET_VRING_KICK] = VHOST_SET_VRING_KICK,
>> +    [VHOST_USER_SET_MEM_TABLE] = VHOST_SET_MEM_TABLE,
>> +};
>> +
>> +/* By default, vhost kernel module allows 64 regions, but DPDK allows
>> + * 256 segments. As a relief, below function merges those virtually
>> + * adjacent memsegs into one region.
>> + */
>> +static struct vhost_memory_kernel *
>> +prepare_vhost_memory_kernel(void)
>> +{
>> +    uint32_t i, j, k = 0;
>> +    struct rte_memseg *seg;
>> +    struct vhost_memory_region *mr;
>> +    struct vhost_memory_kernel *vm;
>> +
>> +    vm = malloc(sizeof(struct vhost_memory_kernel) +
>> +            VHOST_KERNEL_MAX_REGIONS *
>> +            sizeof(struct vhost_memory_region));
>> +
>> +    for (i = 0; i < RTE_MAX_MEMSEG; ++i) {
>> +        seg = &rte_eal_get_configuration()->mem_config->memseg[i];
>> +        if (!seg->addr)
>> +            break;
>
> If we're sure the number of regions is less than 64(or the module 
> parameter read from /sys), can we avoid the iteration here?

The "if" statement under the "for" statement can save us from all 
RTE_MAX_MEMSEG iteration.

>
>> +
>> +        int new_region = 1;
>> +
>> +        for (j = 0; j < k; ++j) {
>> +            mr = &vm->regions[j];
>> +
>> +            if (mr->userspace_addr + mr->memory_size ==
>> +                (uint64_t)seg->addr) {
>> +                mr->memory_size += seg->len;
>> +                new_region = 0;
>> +                break;
>> +            }
>> +
>> +            if ((uint64_t)seg->addr + seg->len ==
>> +                mr->userspace_addr) {
>> +                mr->guest_phys_addr = (uint64_t)seg->addr;
>> +                mr->userspace_addr = (uint64_t)seg->addr;
>> +                mr->memory_size += seg->len;
>> +                new_region = 0;
>> +                break;
>> +            }
>> +        }
>> +
>> +        if (new_region == 0)
>> +            continue;
>> +
>> +        mr = &vm->regions[k++];
>> +        mr->guest_phys_addr = (uint64_t)seg->addr; /* use vaddr 
>> here! */
>> +        mr->userspace_addr = (uint64_t)seg->addr;
>> +        mr->memory_size = seg->len;
>> +        mr->mmap_offset = 0;
>> +
>> +        if (k >= VHOST_KERNEL_MAX_REGIONS) {
>> +            free(vm);
>> +            return NULL;
>> +        }
>> +    }
>> +
>> +    vm->nregions = k;
>> +    vm->padding = 0;
>> +    return vm;
>> +}
>> +
>> +static int
>> +vhost_kernel_ioctl(struct virtio_user_dev *dev,
>> +           enum vhost_user_request req,
>> +           void *arg)
>> +{
>> +    int i, ret = -1;
>> +    uint64_t req_kernel;
>> +    struct vhost_memory_kernel *vm = NULL;
>> +
>> +    req_kernel = vhost_req_user_to_kernel[req];
>> +
>> +    if (req_kernel == VHOST_SET_MEM_TABLE) {
>> +        vm = prepare_vhost_memory_kernel();
>> +        if (!vm)
>> +            return -1;
>> +        arg = (void *)vm;
>> +    }
>> +
>> +    /* Does not work when VIRTIO_F_IOMMU_PLATFORM now, why? */
>
> I think the reason is when VIRTIO_F_IOMMU_PLATFORM is negotiated, all 
> address should be iova instead of gpa.
>

Yes, I agree. As we don't have to do memory protection in a single 
process, so it's completely useless here, right?

>> +    if (req_kernel == VHOST_SET_FEATURES)
>> +        *(uint64_t *)arg &= ~(1ULL << VIRTIO_F_IOMMU_PLATFORM);
>> +
>> +    for (i = 0; i < VHOST_KERNEL_MAX_QUEUES; ++i) {
>> +        if (dev->vhostfds[i] < 0)
>> +            continue;
>> +
[...]
>> +    if (!enable) {
>> +        if (dev->tapfds[pair_idx]) {
>> +            close(dev->tapfds[pair_idx]);
>> +            dev->tapfds[pair_idx] = -1;
>> +        }
>> +        return vhost_kernel_set_backend(vhostfd, -1);
>
> If this is used to for thing like ethtool -L in guest, we should use 
> TUNSETQUEUE here.

Oops, I was missing this ioctl operation. Let me fix it in next version.

>
>> +    } else if (dev->tapfds[pair_idx] >= 0) {
>> +        return 0;
>> +    }
>> +
>> +    if ((dev->features & (1ULL << VIRTIO_NET_F_MRG_RXBUF)) ||
>> +        (dev->features & (1ULL << VIRTIO_F_VERSION_1)))
>> +        hdr_size = sizeof(struct virtio_net_hdr_mrg_rxbuf);
>> +    else
>> +        hdr_size = sizeof(struct virtio_net_hdr);
>> +
>> +    /* TODO:
>> +     * 1. verify we can get/set vnet_hdr_len, tap_probe_vnet_hdr_len
>> +     * 2. get number of memory regions from vhost module parameter
>> +     * max_mem_regions, supported in newer version linux kernel
>> +     */
>> +    tapfd = open(PATH_NET_TUN, O_RDWR);
>> +    if (tapfd < 0) {
>> +        PMD_DRV_LOG(ERR, "fail to open %s: %s",
>> +                PATH_NET_TUN, strerror(errno));
>> +        return -1;
>> +    }
>> +
>> +    /* Construct ifr */
>> +    memset(&ifr, 0, sizeof(ifr));
>> +    ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
>> +
>> +    if (ioctl(tapfd, TUNGETFEATURES, &features) == -1) {
>> +        PMD_DRV_LOG(ERR, "TUNGETFEATURES failed: %s", strerror(errno));
>> +        goto error;
>> +    }
>> +    if (features & IFF_ONE_QUEUE)
>> +        ifr.ifr_flags |= IFF_ONE_QUEUE;
>> +
>> +    /* Let tap instead of vhost-net handle vnet header, as the 
>> latter does
>> +     * not support offloading. And in this case, we should not set 
>> feature
>> +     * bit VHOST_NET_F_VIRTIO_NET_HDR.
>> +     */
>> +    if (features & IFF_VNET_HDR) {
>> +        ifr.ifr_flags |= IFF_VNET_HDR;
>> +    } else {
>> +        PMD_DRV_LOG(ERR, "TAP does not support IFF_VNET_HDR");
>> +        goto error;
>> +    }
>> +
>> +    if (dev->ifname)
>> +        strncpy(ifr.ifr_name, dev->ifname, IFNAMSIZ);
>> +    else
>> +        strncpy(ifr.ifr_name, "tap%d", IFNAMSIZ);
>> +    if (ioctl(tapfd, TUNSETIFF, (void *)&ifr) == -1) {
>> +        PMD_DRV_LOG(ERR, "TUNSETIFF failed: %s", strerror(errno));
>> +        goto error;
>> +    }
>
> This requires CAP_NET_ADMIN, so we should really consider to accept a 
> pre-created fd here.

It sounds like a future work for me. So far, all DPDK apps are running 
in privileged mode (including CAP_NET_ADMIN?).

>
>> +
>> +    fcntl(tapfd, F_SETFL, O_NONBLOCK);
>> +
>> +    if (ioctl(tapfd, TUNSETVNETHDRSZ, &hdr_size) < 0) {
>> +        PMD_DRV_LOG(ERR, "TUNSETVNETHDRSZ failed: %s", 
>> strerror(errno));
>> +        goto error;
>> +    }
>> +
>> +    if (ioctl(tapfd, TUNSETSNDBUF, &sndbuf) < 0) {
>> +        PMD_DRV_LOG(ERR, "TUNSETSNDBUF failed: %s", strerror(errno));
>> +        goto error;
>> +    }
>
> Let's use INT_MAX as default here to survive from evil consumer here.

Oh yes, I will fix it.

Thanks,
Jianfeng