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Subject[PATCH 4.14 077/110] s390/qeth: fix overestimated count of buffer elements
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Julian Wiedmann <jwi@linux.vnet.ibm.com>


[ Upstream commit 12472af89632beb1ed8dea29d4efe208ca05b06a ]

qeth_get_elements_for_range() doesn't know how to handle a 0-length
range (ie. start == end), and returns 1 when it should return 0.
Such ranges occur on TSO skbs, where the L2/L3/L4 headers (and thus all
of the skb's linear data) are skipped when mapping the skb into regular
buffer elements.

This overestimation may cause several performance-related issues:
1. sub-optimal IO buffer selection, where the next buffer gets selected
even though the skb would actually still fit into the current buffer.
2. forced linearization, if the element count for a non-linear skb
exceeds QETH_MAX_BUFFER_ELEMENTS.

Rather than modifying qeth_get_elements_for_range() and adding overhead
to every caller, fix up those callers that are in risk of passing a
0-length range.

Fixes: 2863c61334aa ("qeth: refactor calculation of SBALE count")
Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/s390/net/qeth_core_main.c | 10 ++++++----
drivers/s390/net/qeth_l3_main.c | 11 ++++++-----
2 files changed, 12 insertions(+), 9 deletions(-)

--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -3861,10 +3861,12 @@ EXPORT_SYMBOL_GPL(qeth_get_elements_for_
int qeth_get_elements_no(struct qeth_card *card,
struct sk_buff *skb, int extra_elems, int data_offset)
{
- int elements = qeth_get_elements_for_range(
- (addr_t)skb->data + data_offset,
- (addr_t)skb->data + skb_headlen(skb)) +
- qeth_get_elements_for_frags(skb);
+ addr_t end = (addr_t)skb->data + skb_headlen(skb);
+ int elements = qeth_get_elements_for_frags(skb);
+ addr_t start = (addr_t)skb->data + data_offset;
+
+ if (start != end)
+ elements += qeth_get_elements_for_range(start, end);

if ((elements + extra_elems) > QETH_MAX_BUFFER_ELEMENTS(card)) {
QETH_DBF_MESSAGE(2, "Invalid size of IP packet "
--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -2633,11 +2633,12 @@ static void qeth_tso_fill_header(struct
static int qeth_l3_get_elements_no_tso(struct qeth_card *card,
struct sk_buff *skb, int extra_elems)
{
- addr_t tcpdptr = (addr_t)tcp_hdr(skb) + tcp_hdrlen(skb);
- int elements = qeth_get_elements_for_range(
- tcpdptr,
- (addr_t)skb->data + skb_headlen(skb)) +
- qeth_get_elements_for_frags(skb);
+ addr_t start = (addr_t)tcp_hdr(skb) + tcp_hdrlen(skb);
+ addr_t end = (addr_t)skb->data + skb_headlen(skb);
+ int elements = qeth_get_elements_for_frags(skb);
+
+ if (start != end)
+ elements += qeth_get_elements_for_range(start, end);

if ((elements + extra_elems) > QETH_MAX_BUFFER_ELEMENTS(card)) {
QETH_DBF_MESSAGE(2,

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