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i40e/i40evf: Limit TSO to 7 descriptors for payload instead of 8 per …
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…packet

This patch addresses a bug introduced based on my interpretation of the
XL710 datasheet.  Specifically section 8.4.1 states that "A single transmit
packet may span up to 8 buffers (up to 8 data descriptors per packet
including both the header and payload buffers)."  It then later goes on to
say that each segment for a TSO obeys the previous rule, however it then
refers to TSO header and the segment payload buffers.

I believe the actual limit for fragments with TSO and a skbuff that has
payload data in the header portion of the buffer is actually only 7
fragments as the skb->data portion counts as 2 buffers, one for the TSO
header, and one for a segment payload buffer.

Fixes: 2d37490 ("i40e/i40evf: Rewrite logic for 8 descriptor per packet check")
Reported-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Acked-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
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Alexander Duyck authored and Jeff Kirsher committed Apr 14, 2016
1 parent a6d3713 commit 3f3f7cb
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Showing 4 changed files with 62 additions and 56 deletions.
49 changes: 24 additions & 25 deletions drivers/net/ethernet/intel/i40e/i40e_txrx.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2594,35 +2594,34 @@ int __i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
}

/**
* __i40e_chk_linearize - Check if there are more than 8 fragments per packet
* __i40e_chk_linearize - Check if there are more than 8 buffers per packet
* @skb: send buffer
*
* Note: Our HW can't scatter-gather more than 8 fragments to build
* a packet on the wire and so we need to figure out the cases where we
* need to linearize the skb.
* Note: Our HW can't DMA more than 8 buffers to build a packet on the wire
* and so we need to figure out the cases where we need to linearize the skb.
*
* For TSO we need to count the TSO header and segment payload separately.
* As such we need to check cases where we have 7 fragments or more as we
* can potentially require 9 DMA transactions, 1 for the TSO header, 1 for
* the segment payload in the first descriptor, and another 7 for the
* fragments.
**/
bool __i40e_chk_linearize(struct sk_buff *skb)
{
const struct skb_frag_struct *frag, *stale;
int gso_size, nr_frags, sum;

/* check to see if TSO is enabled, if so we may get a repreive */
gso_size = skb_shinfo(skb)->gso_size;
if (unlikely(!gso_size))
return true;
int nr_frags, sum;

/* no need to check if number of frags is less than 8 */
/* no need to check if number of frags is less than 7 */
nr_frags = skb_shinfo(skb)->nr_frags;
if (nr_frags < I40E_MAX_BUFFER_TXD)
if (nr_frags < (I40E_MAX_BUFFER_TXD - 1))
return false;

/* We need to walk through the list and validate that each group
* of 6 fragments totals at least gso_size. However we don't need
* to perform such validation on the first or last 6 since the first
* 6 cannot inherit any data from a descriptor before them, and the
* last 6 cannot inherit any data from a descriptor after them.
* to perform such validation on the last 6 since the last 6 cannot
* inherit any data from a descriptor after them.
*/
nr_frags -= I40E_MAX_BUFFER_TXD - 1;
nr_frags -= I40E_MAX_BUFFER_TXD - 2;
frag = &skb_shinfo(skb)->frags[0];

/* Initialize size to the negative value of gso_size minus 1. We
Expand All @@ -2631,21 +2630,21 @@ bool __i40e_chk_linearize(struct sk_buff *skb)
* descriptors for a single transmit as the header and previous
* fragment are already consuming 2 descriptors.
*/
sum = 1 - gso_size;
sum = 1 - skb_shinfo(skb)->gso_size;

/* Add size of frags 1 through 5 to create our initial sum */
sum += skb_frag_size(++frag);
sum += skb_frag_size(++frag);
sum += skb_frag_size(++frag);
sum += skb_frag_size(++frag);
sum += skb_frag_size(++frag);
/* Add size of frags 0 through 4 to create our initial sum */
sum += skb_frag_size(frag++);
sum += skb_frag_size(frag++);
sum += skb_frag_size(frag++);
sum += skb_frag_size(frag++);
sum += skb_frag_size(frag++);

/* Walk through fragments adding latest fragment, testing it, and
* then removing stale fragments from the sum.
*/
stale = &skb_shinfo(skb)->frags[0];
for (;;) {
sum += skb_frag_size(++frag);
sum += skb_frag_size(frag++);

/* if sum is negative we failed to make sufficient progress */
if (sum < 0)
Expand All @@ -2655,7 +2654,7 @@ bool __i40e_chk_linearize(struct sk_buff *skb)
if (!--nr_frags)
break;

sum -= skb_frag_size(++stale);
sum -= skb_frag_size(stale++);
}

return false;
Expand Down
10 changes: 7 additions & 3 deletions drivers/net/ethernet/intel/i40e/i40e_txrx.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -413,10 +413,14 @@ static inline int i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
**/
static inline bool i40e_chk_linearize(struct sk_buff *skb, int count)
{
/* we can only support up to 8 data buffers for a single send */
if (likely(count <= I40E_MAX_BUFFER_TXD))
/* Both TSO and single send will work if count is less than 8 */
if (likely(count < I40E_MAX_BUFFER_TXD))
return false;

return __i40e_chk_linearize(skb);
if (skb_is_gso(skb))
return __i40e_chk_linearize(skb);

/* we can support up to 8 data buffers for a single send */
return count != I40E_MAX_BUFFER_TXD;
}
#endif /* _I40E_TXRX_H_ */
49 changes: 24 additions & 25 deletions drivers/net/ethernet/intel/i40evf/i40e_txrx.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1796,35 +1796,34 @@ static void i40e_create_tx_ctx(struct i40e_ring *tx_ring,
}

/**
* __i40evf_chk_linearize - Check if there are more than 8 fragments per packet
* __i40evf_chk_linearize - Check if there are more than 8 buffers per packet
* @skb: send buffer
*
* Note: Our HW can't scatter-gather more than 8 fragments to build
* a packet on the wire and so we need to figure out the cases where we
* need to linearize the skb.
* Note: Our HW can't DMA more than 8 buffers to build a packet on the wire
* and so we need to figure out the cases where we need to linearize the skb.
*
* For TSO we need to count the TSO header and segment payload separately.
* As such we need to check cases where we have 7 fragments or more as we
* can potentially require 9 DMA transactions, 1 for the TSO header, 1 for
* the segment payload in the first descriptor, and another 7 for the
* fragments.
**/
bool __i40evf_chk_linearize(struct sk_buff *skb)
{
const struct skb_frag_struct *frag, *stale;
int gso_size, nr_frags, sum;

/* check to see if TSO is enabled, if so we may get a repreive */
gso_size = skb_shinfo(skb)->gso_size;
if (unlikely(!gso_size))
return true;
int nr_frags, sum;

/* no need to check if number of frags is less than 8 */
/* no need to check if number of frags is less than 7 */
nr_frags = skb_shinfo(skb)->nr_frags;
if (nr_frags < I40E_MAX_BUFFER_TXD)
if (nr_frags < (I40E_MAX_BUFFER_TXD - 1))
return false;

/* We need to walk through the list and validate that each group
* of 6 fragments totals at least gso_size. However we don't need
* to perform such validation on the first or last 6 since the first
* 6 cannot inherit any data from a descriptor before them, and the
* last 6 cannot inherit any data from a descriptor after them.
* to perform such validation on the last 6 since the last 6 cannot
* inherit any data from a descriptor after them.
*/
nr_frags -= I40E_MAX_BUFFER_TXD - 1;
nr_frags -= I40E_MAX_BUFFER_TXD - 2;
frag = &skb_shinfo(skb)->frags[0];

/* Initialize size to the negative value of gso_size minus 1. We
Expand All @@ -1833,21 +1832,21 @@ bool __i40evf_chk_linearize(struct sk_buff *skb)
* descriptors for a single transmit as the header and previous
* fragment are already consuming 2 descriptors.
*/
sum = 1 - gso_size;
sum = 1 - skb_shinfo(skb)->gso_size;

/* Add size of frags 1 through 5 to create our initial sum */
sum += skb_frag_size(++frag);
sum += skb_frag_size(++frag);
sum += skb_frag_size(++frag);
sum += skb_frag_size(++frag);
sum += skb_frag_size(++frag);
/* Add size of frags 0 through 4 to create our initial sum */
sum += skb_frag_size(frag++);
sum += skb_frag_size(frag++);
sum += skb_frag_size(frag++);
sum += skb_frag_size(frag++);
sum += skb_frag_size(frag++);

/* Walk through fragments adding latest fragment, testing it, and
* then removing stale fragments from the sum.
*/
stale = &skb_shinfo(skb)->frags[0];
for (;;) {
sum += skb_frag_size(++frag);
sum += skb_frag_size(frag++);

/* if sum is negative we failed to make sufficient progress */
if (sum < 0)
Expand All @@ -1857,7 +1856,7 @@ bool __i40evf_chk_linearize(struct sk_buff *skb)
if (!--nr_frags)
break;

sum -= skb_frag_size(++stale);
sum -= skb_frag_size(stale++);
}

return false;
Expand Down
10 changes: 7 additions & 3 deletions drivers/net/ethernet/intel/i40evf/i40e_txrx.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -395,10 +395,14 @@ static inline int i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
**/
static inline bool i40e_chk_linearize(struct sk_buff *skb, int count)
{
/* we can only support up to 8 data buffers for a single send */
if (likely(count <= I40E_MAX_BUFFER_TXD))
/* Both TSO and single send will work if count is less than 8 */
if (likely(count < I40E_MAX_BUFFER_TXD))
return false;

return __i40evf_chk_linearize(skb);
if (skb_is_gso(skb))
return __i40evf_chk_linearize(skb);

/* we can support up to 8 data buffers for a single send */
return count != I40E_MAX_BUFFER_TXD;
}
#endif /* _I40E_TXRX_H_ */

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