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Date: Mon, 19 Feb 2024 20:13:49 +0000
From: Simon Horman <horms@...nel.org>
To: Christian Hopps <chopps@...pps.org>
Cc: devel@...ux-ipsec.org, Steffen Klassert <steffen.klassert@...unet.com>,
netdev@...r.kernel.org, Christian Hopps <chopps@...n.net>
Subject: Re: [PATCH ipsec-next v1 8/8] iptfs: impl: add new iptfs xfrm mode
impl
On Mon, Feb 19, 2024 at 03:57:35AM -0500, Christian Hopps wrote:
> From: Christian Hopps <chopps@...n.net>
>
> Add a new xfrm mode implementing AggFrag/IP-TFS from RFC9347.
>
> This utilizes the new xfrm_mode_cbs to implement demand-driven IP-TFS
> functionality. This functionality can be used to increase bandwidth
> utilization through small packet aggregation, as well as help solve PMTU
> issues through it's efficient use of fragmentation.
>
> Link: https://www.rfc-editor.org/rfc/rfc9347.txt
>
> Signed-off-by: Christian Hopps <chopps@...n.net>
...
> diff --git a/net/xfrm/xfrm_iptfs.c b/net/xfrm/xfrm_iptfs.c
...
> +/**
> + * skb_head_to_frag() - initialize a skb_frag_t based on skb head data
> + * @skb: skb with the head data
> + * @frag: frag to initialize
> + */
> +static void skb_head_to_frag(const struct sk_buff *skb, skb_frag_t *frag)
> +{
> + struct page *page = virt_to_head_page(skb->data);
> + unsigned char *addr = (unsigned char *)page_address(page);
> +
> + BUG_ON(!skb->head_frag);
Is it strictly necessary to crash the Kernel here?
Likewise, many other places in this patch.
> + skb_frag_fill_page_desc(frag, page, skb->data - addr, skb_headlen(skb));
> +}
...
> +/**
> + * skb_add_frags() - add a range of fragment references into an skb
> + * @skb: skb to add references into
> + * @walk: the walk to add referenced fragments from.
> + * @offset: offset from beginning of original skb to start from.
> + * @len: amount of data to add frag references to in @skb.
> + *
> + * skb_can_add_frags() should be called before this function to verify that the
> + * destination @skb is compatible with the walk and has space in the array for
> + * the to be added frag refrences.
nit: references
> + *
> + * Return: The number of bytes not added to @skb b/c we reached the end of the
> + * walk before adding all of @len.
> + */
...
> +/**
> + * iptfs_reassem_done() - In-progress packet is aborted free the state.
nit: This does not match the name of the function it documents.
Flagged by W=1 build with gcc-13.
> + * @xtfs: xtfs state
> + */
> +static void iptfs_reassem_abort(struct xfrm_iptfs_data *xtfs)
> +{
> + __iptfs_reassem_done(xtfs, true);
> +}
...
> +/**
> + * iptfs_input_ordered() - handle next in order IPTFS payload.
> + * @x: xfrm state
> + * @skb: current packet
> + *
> + * Process the IPTFS payload in `skb` and consume it afterwards.
> + */
> +static int iptfs_input_ordered(struct xfrm_state *x, struct sk_buff *skb)
> +{
> + u8 hbytes[sizeof(struct ipv6hdr)];
> + struct ip_iptfs_cc_hdr iptcch;
> + struct skb_seq_state skbseq;
> + struct skb_frag_walk _fragwalk;
> + struct skb_frag_walk *fragwalk = NULL;
> + struct list_head sublist; /* rename this it's just a list */
> + struct sk_buff *first_skb, *defer, *next;
> + const unsigned char *old_mac;
> + struct xfrm_iptfs_data *xtfs;
> + struct ip_iptfs_hdr *ipth;
> + struct iphdr *iph;
> + struct net *net;
> + u32 remaining, first_iplen, iplen, iphlen, data, tail;
> + u32 blkoff, capturelen;
> + u64 seq;
> +
> + xtfs = x->mode_data;
> + net = dev_net(skb->dev);
> + first_skb = NULL;
> + defer = NULL;
> +
> + seq = __esp_seq(skb);
> +
> + /* Large enough to hold both types of header */
> + ipth = (struct ip_iptfs_hdr *)&iptcch;
> +
> + /* Save the old mac header if set */
> + old_mac = skb_mac_header_was_set(skb) ? skb_mac_header(skb) : NULL;
> +
> + skb_prepare_seq_read(skb, 0, skb->len, &skbseq);
> +
> + /* Get the IPTFS header and validate it */
> +
> + if (skb_copy_bits_seq(&skbseq, 0, ipth, sizeof(*ipth))) {
> + XFRM_INC_STATS(net, LINUX_MIB_XFRMINBUFFERERROR);
> + goto done;
> + }
> + data = sizeof(*ipth);
> +
> + trace_iptfs_egress_recv(skb, xtfs, htons(ipth->block_offset));
Maybe this is backwards, because the argument to htons should be
in host byte order, but the type of ipth->block_offset is __be16.
Also, personally, i would suggest using be16_to_cpu as it better
describes the types involved.
This is flagged by Sparse along with some other problems.
Please take care not to introduce new Sparse warnings.
...
> +static u32 __reorder_future_shifts(struct xfrm_iptfs_data *xtfs,
> + struct sk_buff *inskb,
> + struct list_head *list,
> + struct list_head *freelist, u32 *fcount)
> +{
> + const u32 nslots = xtfs->cfg.reorder_win_size + 1;
> + const u64 inseq = __esp_seq(inskb);
> + u32 savedlen = xtfs->w_savedlen;
> + u64 wantseq = xtfs->w_wantseq;
> + struct sk_buff *slot0 = NULL;
> + u64 last_drop_seq = xtfs->w_wantseq;
> + u64 distance, extra_drops, missed, s0seq;
Missed is set but otherwise unused in this function.
Flagged by W=1 build with clang-17.
> + u32 count = 0;
> + struct skb_wseq *wnext;
> + u32 beyond, shifting, slot;
> +
> + BUG_ON(inseq <= wantseq);
> + distance = inseq - wantseq;
> + BUG_ON(distance <= nslots - 1);
> + beyond = distance - (nslots - 1);
> + missed = 0;
> +
> + /* Handle future sequence number received.
> + *
> + * IMPORTANT: we are at least advancing w_wantseq (i.e., wantseq) by 1
> + * b/c we are beyond the window boundary.
> + *
> + * We know we don't have the wantseq so that counts as a drop.
> + */
> +
> + /* ex: slot count is 4, array size is 3 savedlen is 2, slot 0 is the
> + * missing sequence number.
> + *
> + * the final slot at savedlen (index savedlen - 1) is always occupied.
> + *
> + * beyond is "beyond array size" not savedlen.
> + *
> + * +--------- array length (savedlen == 2)
> + * | +----- array size (nslots - 1 == 3)
> + * | | +- window boundary (nslots == 4)
> + * V V | V
> + * |
> + * 0 1 2 3 | slot number
> + * --- 0 1 2 | array index
> + * [b] [c] : :| array
> + * |
> + * "2" "3" "4" "5"|*6* seq numbers
> + *
> + * We receive seq number 6
> + * distance == 4 [inseq(6) - w_wantseq(2)]
> + * newslot == distance
> + * index == 3 [distance(4) - 1]
> + * beyond == 1 [newslot(4) - lastslot((nslots(4) - 1))]
> + * shifting == 1 [min(savedlen(2), beyond(1)]
> + * slot0_skb == [b], and should match w_wantseq
> + *
> + * +--- window boundary (nslots == 4)
> + * 0 1 2 3 | 4 slot number
> + * --- 0 1 2 | 3 array index
> + * [b] : : : :| array
> + * "2" "3" "4" "5" *6* seq numbers
> + *
> + * We receive seq number 6
> + * distance == 4 [inseq(6) - w_wantseq(2)]
> + * newslot == distance
> + * index == 3 [distance(4) - 1]
> + * beyond == 1 [newslot(4) - lastslot((nslots(4) - 1))]
> + * shifting == 1 [min(savedlen(1), beyond(1)]
> + * slot0_skb == [b] and should match w_wantseq
> + *
> + * +-- window boundary (nslots == 4)
> + * 0 1 2 3 | 4 5 6 slot number
> + * --- 0 1 2 | 3 4 5 array index
> + * [-] [c] : :| array
> + * "2" "3" "4" "5" "6" "7" *8* seq numbers
> + *
> + * savedlen = 2, beyond = 3
> + * iter 1: slot0 == NULL, missed++, lastdrop = 2 (2+1-1), slot0 = [-]
> + * iter 2: slot0 == NULL, missed++, lastdrop = 3 (2+2-1), slot0 = [c]
> + * 2 < 3, extra = 1 (3-2), missed += extra, lastdrop = 4 (2+2+1-1)
> + *
> + * We receive seq number 8
> + * distance == 6 [inseq(8) - w_wantseq(2)]
> + * newslot == distance
> + * index == 5 [distance(6) - 1]
> + * beyond == 3 [newslot(6) - lastslot((nslots(4) - 1))]
> + * shifting == 2 [min(savedlen(2), beyond(3)]
> + *
> + * slot0_skb == NULL changed from [b] when "savedlen < beyond" is true.
> + */
> +
> + /* Now send any packets that are being shifted out of saved, and account
> + * for missing packets that are exiting the window as we shift it.
> + */
> +
> + /* If savedlen > beyond we are shifting some, else all. */
> + shifting = min(savedlen, beyond);
> +
> + /* slot0 is the buf that just shifted out and into slot0 */
> + slot0 = NULL;
> + s0seq = wantseq;
> + last_drop_seq = s0seq;
> + wnext = xtfs->w_saved;
> + for (slot = 1; slot <= shifting; slot++, wnext++) {
> + /* handle what was in slot0 before we occupy it */
> + if (!slot0) {
> + last_drop_seq = s0seq;
> + missed++;
> + } else {
> + list_add_tail(&slot0->list, list);
> + count++;
> + }
> + s0seq++;
> + slot0 = wnext->skb;
> + wnext->skb = NULL;
> + }
> +
> + /* slot0 is now either NULL (in which case it's what we now are waiting
> + * for, or a buf in which case we need to handle it like we received it;
> + * however, we may be advancing past that buffer as well..
> + */
> +
> + /* Handle case where we need to shift more than we had saved, slot0 will
> + * be NULL iff savedlen is 0, otherwise slot0 will always be
> + * non-NULL b/c we shifted the final element, which is always set if
> + * there is any saved, into slot0.
> + */
> + if (savedlen < beyond) {
> + extra_drops = beyond - savedlen;
> + if (savedlen == 0) {
> + BUG_ON(slot0);
> + s0seq += extra_drops;
> + last_drop_seq = s0seq - 1;
> + } else {
> + extra_drops--; /* we aren't dropping what's in slot0 */
> + BUG_ON(!slot0);
> + list_add_tail(&slot0->list, list);
> + /* if extra_drops then we are going past this slot0
> + * so we can safely advance last_drop_seq
> + */
> + if (extra_drops)
> + last_drop_seq = s0seq + extra_drops;
> + s0seq += extra_drops + 1;
> + count++;
> + }
> + missed += extra_drops;
> + slot0 = NULL;
> + /* slot0 has had an empty slot pushed into it */
> + }
> + (void)last_drop_seq; /* we want this for CC code */
> +
> + /* Remove the entries */
> + __vec_shift(xtfs, beyond);
> +
> + /* Advance want seq */
> + xtfs->w_wantseq += beyond;
> +
> + /* Process drops here when implementing congestion control */
> +
> + /* We've shifted. plug the packet in at the end. */
> + xtfs->w_savedlen = nslots - 1;
> + xtfs->w_saved[xtfs->w_savedlen - 1].skb = inskb;
> + iptfs_set_window_drop_times(xtfs, xtfs->w_savedlen - 1);
> +
> + /* if we don't have a slot0 then we must wait for it */
> + if (!slot0)
> + return count;
> +
> + /* If slot0, seq must match new want seq */
> + BUG_ON(xtfs->w_wantseq != __esp_seq(slot0));
> +
> + /* slot0 is valid, treat like we received expected. */
> + count += __reorder_this(xtfs, slot0, list);
> + return count;
> +}
...
> +/**
> + * iptfs_get_mtu() - return the inner MTU for an IPTFS xfrm.
nit: This does not match the name of the function it documents.
> + * @x: xfrm state.
> + * @outer_mtu: Outer MTU for the encapsulated packet.
> + *
> + * Return: Correct MTU taking in to account the encap overhead.
> + */
> +static u32 iptfs_get_inner_mtu(struct xfrm_state *x, int outer_mtu)
...
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