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SubjectRe: [PATCH net-next v7 4/9] xen-netback: Introduce TX grant mapping
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On Thu, 2014-03-06 at 21:48 +0000, Zoltan Kiss wrote:
> @@ -135,13 +146,31 @@ struct xenvif {
> pending_ring_idx_t pending_cons;
> u16 pending_ring[MAX_PENDING_REQS];
> struct pending_tx_info pending_tx_info[MAX_PENDING_REQS];
> + grant_handle_t grant_tx_handle[MAX_PENDING_REQS];
>
> /* Coalescing tx requests before copying makes number of grant
> * copy ops greater or equal to number of slots required. In
> * worst case a tx request consumes 2 gnttab_copy.
> */
> struct gnttab_copy tx_copy_ops[2*MAX_PENDING_REQS];
> -
> + struct gnttab_map_grant_ref tx_map_ops[MAX_PENDING_REQS];
> + struct gnttab_unmap_grant_ref tx_unmap_ops[MAX_PENDING_REQS];

I wonder if we should break some of these arrays into separate
allocations? Wasn't there a problem with sizeof(struct xenvif) at one
point?

> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
> index bc32627..1fe9fe5 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -493,6 +533,23 @@ void xenvif_disconnect(struct xenvif *vif)
>
> void xenvif_free(struct xenvif *vif)
> {
> + int i, unmap_timeout = 0;
> +
> + for (i = 0; i < MAX_PENDING_REQS; ++i) {
> + if (vif->grant_tx_handle[i] != NETBACK_INVALID_HANDLE) {
> + unmap_timeout++;
> + schedule_timeout(msecs_to_jiffies(1000));
> + if (unmap_timeout > 9 &&
> + net_ratelimit())

Does this really reach 80 columns when unwrapped?

(there seems to my eye to be a lot of overaggressive wrapping in this
patch, but nevermind)

> + netdev_err(vif->dev,
> + "Page still granted! Index: %x\n",
> + i);
> + i = -1;

Should there not be a break here? Otherwise don't we restart the for
loop from 0 again? If that is intentional then a comment would be very
useful.

> @@ -919,11 +873,38 @@ err:
> return NULL;
> }
>
> +static inline void xenvif_grant_handle_set(struct xenvif *vif,
> + u16 pending_idx,
> + grant_handle_t handle)
> +{
> + if (unlikely(vif->grant_tx_handle[pending_idx] !=
> + NETBACK_INVALID_HANDLE)) {
> + netdev_err(vif->dev,

Is this in any way guest triggerable? Needs to be ratelimited in that
case (and arguably even if not?)

> + "Trying to overwrite active handle! pending_idx: %x\n",
> + pending_idx);
> + BUG();
> + }
> + vif->grant_tx_handle[pending_idx] = handle;
> +}
> +
> +static inline void xenvif_grant_handle_reset(struct xenvif *vif,
> + u16 pending_idx)
> +{
> + if (unlikely(vif->grant_tx_handle[pending_idx] ==
> + NETBACK_INVALID_HANDLE)) {
> + netdev_err(vif->dev,

Likewise.

> + "Trying to unmap invalid handle! pending_idx: %x\n",
> + pending_idx);
> + BUG();
> + }
> + vif->grant_tx_handle[pending_idx] = NETBACK_INVALID_HANDLE;
> +}
> +
> @@ -1001,6 +982,17 @@ static void xenvif_fill_frags(struct xenvif *vif, struct sk_buff *skb)
>
> pending_idx = frag_get_pending_idx(frag);
>
> + /* If this is not the first frag, chain it to the previous*/
> + if (unlikely(prev_pending_idx == INVALID_PENDING_IDX))
> + skb_shinfo(skb)->destructor_arg =
> + &vif->pending_tx_info[pending_idx].callback_struct;
> + else if (likely(pending_idx != prev_pending_idx))
> + vif->pending_tx_info[prev_pending_idx].callback_struct.ctx =
> + &(vif->pending_tx_info[pending_idx].callback_struct);

#define callback_for(vif, pending_idx) .... would make this and a bunch
of other places a lot less verbose IMHO.

> + index = pending_index(vif->pending_prod);
> + vif->pending_ring[index] = pending_idx;
> + /* TX shouldn't use the index before we give it back here */

I hope this comment refers to the pending_prod++ and not the mb(), since
the barrier only guarantees visibility after that point, but not
invisibility before this point.

[...]
> + /* Btw. already unmapped? */

What does this comment mean? Is it a fixme? An indicator that
xenvif_grant_handle_reset is supposed to handle this case or something
else?

I think there was another such comment earlier too.
> + xenvif_grant_handle_reset(vif, pending_idx);
> +
> + ret = gnttab_unmap_refs(&tx_unmap_op, NULL,
> + &vif->mmap_pages[pending_idx], 1);
> + BUG_ON(ret);
> +
> + xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_OKAY);
> +}
> +
> static inline int rx_work_todo(struct xenvif *vif)
> {
> return !skb_queue_empty(&vif->rx_queue) &&




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