Re: [PATCH v5 10/15] argo: implement the notify op

["Roger Pau Monné" <roger.pau@citrix.com>]

On Mon, Jan 21, 2019 at 01:59:50AM -0800, Christopher Clark wrote:
> Queries for data about space availability in registered rings and
> causes notification to be sent when space has become available.
> 
> The hypercall op populates a supplied data structure with information about
> ring state and if insufficient space is currently available in a given ring,
> the hypervisor will record the domain's expressed interest and notify it
> when it observes that space has become available.
> 
> Checks for free space occur when this notify op is invoked, so it may be
> intentionally invoked with no data structure to populate
> (ie. a NULL argument) to trigger such a check and consequent notifications.
> 
> Limit the maximum number of notify requests in a single operation to a
> simple fixed limit of 256.
> 
> Signed-off-by: Christopher Clark <christopher.clark6@baesystems.com>

LGTM, but I would like to see the open-coded versions of the list_
macros fixed:

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

> diff --git a/xen/common/argo.c b/xen/common/argo.c
> index 518aff7..4b43bdd 100644
> --- a/xen/common/argo.c
> +++ b/xen/common/argo.c
[...]
> +static void
> +pending_notify(struct list_head *to_notify)
> +{
> +    ASSERT(LOCKING_Read_L1);
> +
> +    /* Sending signals for all ents in this list, draining until it is empty. */
> +    while ( !list_empty(to_notify) )
> +    {
> +        struct pending_ent *ent =
> +            list_entry(to_notify->next, struct pending_ent, node);

list_first_entry_or_null

> +
> +        list_del(&ent->node);
> +        signal_domid(ent->domain_id);
> +        xfree(ent);
> +    }
> +}
> +
> +static void
> +pending_find(const struct domain *d, struct argo_ring_info *ring_info,
> +             unsigned int payload_space, struct list_head *to_notify)
> +{
> +    struct list_head *cursor, *pending_head;
> +
> +    ASSERT(LOCKING_Read_rings_L2(d));
> +
> +    /*
> +     * TODO: Current policy here is to signal _all_ of the waiting domains
> +     *       interested in sending a message of size less than payload_space.
> +     *
> +     * This is likely to be suboptimal, since once one of them has added
> +     * their message to the ring, there may well be insufficient room
> +     * available for any of the others to transmit, meaning that they were
> +     * woken in vain, which created extra work just to requeue their wait.
> +     *
> +     * Retain this simple policy for now since it at least avoids starving a
> +     * domain of available space notifications because of a policy that only
> +     * notified other domains instead. Improvement may be possible;
> +     * investigation required.
> +     */
> +    spin_lock(&ring_info->L3_lock);
> +
> +    /* Remove matching ents from the ring list, and add them to "to_notify" */
> +    pending_head = &ring_info->pending;
> +    cursor = pending_head->next;
> +
> +    while ( cursor != pending_head )
> +    {
> +        struct pending_ent *ent = list_entry(cursor, struct pending_ent, node);
> +
> +        cursor = cursor->next;

list_for_each_entry_safe?

> +
> +        if ( payload_space >= ent->len )
> +        {
> +            if ( ring_info->id.partner_id == XEN_ARGO_DOMID_ANY )
> +                wildcard_pending_list_remove(ent->domain_id, ent);
> +
> +            list_del(&ent->node);
> +            ring_info->npending--;
> +            list_add(&ent->node, to_notify);
> +        }
> +    }
> +
> +    spin_unlock(&ring_info->L3_lock);
> +}
> +
>  static int
>  pending_queue(const struct domain *d, struct argo_ring_info *ring_info,
>                domid_t src_id, unsigned int len)
> @@ -1023,6 +1163,36 @@ pending_requeue(const struct domain *d, struct argo_ring_info *ring_info,
>  }
>  
>  static void
> +pending_cancel(const struct domain *d, struct argo_ring_info *ring_info,
> +               domid_t src_id)
> +{
> +    struct list_head *cursor, *pending_head;
> +
> +    ASSERT(LOCKING_L3(d, ring_info));
> +
> +    /* Remove all ents where domain_id matches src_id from the ring's list. */
> +    pending_head = &ring_info->pending;
> +    cursor = pending_head->next;
> +
> +    while ( cursor != pending_head )
> +    {
> +        struct pending_ent *ent = list_entry(cursor, struct pending_ent, node);
> +
> +        cursor = cursor->next;

list_for_each_entry_safe

> +
> +        if ( ent->domain_id == src_id )
> +        {
> +            /* For wildcard rings, remove each from their wildcard list too. */
> +            if ( ring_info->id.partner_id == XEN_ARGO_DOMID_ANY )
> +                wildcard_pending_list_remove(ent->domain_id, ent);
> +            list_del(&ent->node);
> +            xfree(ent);
> +            ring_info->npending--;
> +        }
> +    }
> +}
> +
> +static void
>  wildcard_rings_pending_remove(struct domain *d)
>  {
>      struct list_head *wildcard_head;
> @@ -1158,6 +1328,86 @@ partner_rings_remove(struct domain *src_d)
>  }
>  
>  static int
> +fill_ring_data(const struct domain *currd,
> +               XEN_GUEST_HANDLE(xen_argo_ring_data_ent_t) data_ent_hnd)
> +{
> +    xen_argo_ring_data_ent_t ent;
> +    struct domain *dst_d;
> +    struct argo_ring_info *ring_info;
> +    int ret = 0;
> +
> +    ASSERT(currd == current->domain);
> +    ASSERT(LOCKING_Read_L1);
> +
> +    if ( __copy_from_guest(&ent, data_ent_hnd, 1) )
> +        return -EFAULT;
> +
> +    argo_dprintk("fill_ring_data: ent.ring.domain=%u,ent.ring.aport=%x\n",
> +                 ent.ring.domain_id, ent.ring.aport);
> +
> +    ent.flags = 0;
> +
> +    dst_d = get_domain_by_id(ent.ring.domain_id);
> +    if ( !dst_d || !dst_d->argo )
> +        goto out;
> +
> +    read_lock(&dst_d->argo->rings_L2_rwlock);
> +
> +    ring_info = find_ring_info_by_match(dst_d, ent.ring.aport,
> +                                        currd->domain_id);
> +    if ( ring_info )
> +    {
> +        unsigned int space_avail;
> +
> +        ent.flags |= XEN_ARGO_RING_EXISTS;
> +
> +        spin_lock(&ring_info->L3_lock);
> +
> +        ent.max_message_size = ring_info->len -
> +                                   sizeof(struct xen_argo_ring_message_header) -
> +                                   ROUNDUP_MESSAGE(1);
> +
> +        if ( ring_info->id.partner_id == XEN_ARGO_DOMID_ANY )
> +            ent.flags |= XEN_ARGO_RING_SHARED;
> +
> +        space_avail = ringbuf_payload_space(dst_d, ring_info);
> +
> +        argo_dprintk("fill_ring_data: aport=%x space_avail=%u"
> +                     " space_wanted=%u\n",
> +                     ring_info->id.aport, space_avail, ent.space_required);
> +
> +        /* Do not queue a notification for an unachievable size */
> +        if ( ent.space_required > ent.max_message_size )
> +            ent.flags |= XEN_ARGO_RING_EMSGSIZE;
> +        else if ( space_avail >= ent.space_required )
> +        {
> +            pending_cancel(dst_d, ring_info, currd->domain_id);
> +            ent.flags |= XEN_ARGO_RING_SUFFICIENT;
> +        }
> +        else
> +            ret = pending_requeue(dst_d, ring_info, currd->domain_id,
> +                                  ent.space_required);
> +
> +        spin_unlock(&ring_info->L3_lock);
> +
> +        if ( space_avail == ent.max_message_size )
> +            ent.flags |= XEN_ARGO_RING_EMPTY;
> +
> +    }
> +    read_unlock(&dst_d->argo->rings_L2_rwlock);
> +
> + out:
> +    if ( dst_d )
> +        put_domain(dst_d);
> +
> +    if ( !ret && (__copy_field_to_guest(data_ent_hnd, &ent, flags) ||
> +                  __copy_field_to_guest(data_ent_hnd, &ent, max_message_size)) )
> +        return -EFAULT;
> +
> +    return ret;
> +}
> +
> +static int
>  find_ring_mfn(struct domain *d, gfn_t gfn, mfn_t *mfn)
>  {
>      struct page_info *page;
> @@ -1586,6 +1836,112 @@ register_ring(struct domain *currd,
>      return ret;
>  }
>  
> +static void
> +notify_ring(const struct domain *d, struct argo_ring_info *ring_info,
> +            struct list_head *to_notify)
> +{
> +    unsigned int space;
> +
> +    ASSERT(LOCKING_Read_rings_L2(d));
> +
> +    spin_lock(&ring_info->L3_lock);
> +
> +    if ( ring_info->len )
> +        space = ringbuf_payload_space(d, ring_info);
> +    else
> +        space = 0;
> +
> +    spin_unlock(&ring_info->L3_lock);
> +
> +    if ( space )
> +        pending_find(d, ring_info, space, to_notify);
> +}
> +
> +static void
> +notify_check_pending(struct domain *d)
> +{
> +    unsigned int i;
> +    LIST_HEAD(to_notify);
> +
> +    ASSERT(LOCKING_Read_L1);
> +
> +    read_lock(&d->argo->rings_L2_rwlock);
> +
> +    /* Walk all rings, call notify_ring on each to populate to_notify list */
> +    for ( i = 0; i < ARGO_HASHTABLE_SIZE; i++ )
> +    {
> +        struct list_head *cursor, *bucket = &d->argo->ring_hash[i];
> +        struct argo_ring_info *ring_info;
> +
> +        for ( cursor = bucket->next; cursor != bucket; cursor = cursor->next )

list_for_each_entry

Roger.

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