Re: [Xen-devel] [PATCH] xen/netfront: handle compound page fragments on transmit
flat view
From: Jan Beulich <hidden>
Date: 2012-11-20 12:27:20
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On 20.11.12 at 12:40, Ian Campbell [off-list ref] wrote:An SKB paged fragment can consist of a compound page with order > 0. However the netchannel protocol deals only in PAGE_SIZE frames. Handle this in xennet_make_frags by iterating over the frames which make up the page. This is the netfront equivalent to 6a8ed462f16b for netback.
Wouldn't you need to be at least a little more conservative here with respect to resource use: I realize that get_id_from_freelist() return values were never checked, and failure of gnttab_claim_grant_reference() was always dealt with via BUG_ON(), but considering that netfront_tx_slot_available() doesn't account for compound page fragments, I think this (lack of) error handling needs improvement in the course of the change here (regardless of - I think - someone having said that usually the sum of all pages referenced from an skb's fragments would not exceed MAX_SKB_FRAGS - "usually" just isn't enough imo). Jan
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Signed-off-by: Ian Campbell <redacted> Cc: netdev@vger.kernel.org Cc: xen-devel@lists.xen.org Cc: Eric Dumazet <redacted> Cc: Konrad Rzeszutek Wilk <konrad@kernel.org> Cc: ANNIE LI <redacted> Cc: Sander Eikelenboom <redacted> Cc: Stefan Bader <redacted> --- drivers/net/xen-netfront.c | 58 +++++++++++++++++++++++++++++++++---------- 1 files changed, 44 insertions(+), 14 deletions(-)diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c index caa0110..a12b99a 100644 --- a/drivers/net/xen-netfront.c +++ b/drivers/net/xen-netfront.c@@ -452,24 +452,54 @@ static void xennet_make_frags(struct sk_buff *skb,struct net_device *dev, /* Grant backend access to each skb fragment page. */ for (i = 0; i < frags; i++) { skb_frag_t *frag = skb_shinfo(skb)->frags + i; + struct page *page = skb_frag_page(frag); + unsigned long size = skb_frag_size(frag); + unsigned long offset = frag->page_offset; - tx->flags |= XEN_NETTXF_more_data; + /* Data must not cross a page boundary. */ + BUG_ON(size + offset > PAGE_SIZE<<compound_order(page)); - id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs); - np->tx_skbs[id].skb = skb_get(skb); - tx = RING_GET_REQUEST(&np->tx, prod++); - tx->id = id; - ref = gnttab_claim_grant_reference(&np->gref_tx_head); - BUG_ON((signed short)ref < 0); + /* Skip unused frames from start of page */ + page += offset >> PAGE_SHIFT; + offset &= ~PAGE_MASK; - mfn = pfn_to_mfn(page_to_pfn(skb_frag_page(frag))); - gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id, - mfn, GNTMAP_readonly); + while (size > 0) { + unsigned long bytes; - tx->gref = np->grant_tx_ref[id] = ref; - tx->offset = frag->page_offset; - tx->size = skb_frag_size(frag); - tx->flags = 0; + BUG_ON(offset >= PAGE_SIZE); + + bytes = PAGE_SIZE - offset; + if (bytes > size) + bytes = size; + + tx->flags |= XEN_NETTXF_more_data; + + id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs); + np->tx_skbs[id].skb = skb_get(skb); + tx = RING_GET_REQUEST(&np->tx, prod++); + tx->id = id; + ref = gnttab_claim_grant_reference(&np->gref_tx_head); + BUG_ON((signed short)ref < 0); + + mfn = pfn_to_mfn(page_to_pfn(page)); + gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id, + mfn, GNTMAP_readonly); + + tx->gref = np->grant_tx_ref[id] = ref; + tx->offset = offset; + tx->size = bytes; + tx->flags = 0; + + offset += bytes; + size -= bytes; + + /* Next frame */ + if (offset == PAGE_SIZE && size) { + BUG_ON(!PageCompound(page)); + page++; + offset = 0; + } + } } np->tx.req_prod_pvt = prod; -- 1.7.2.5 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel