[PATCH net] gve: Fix XDP TX completion handling when counters overflow

[PATCH net] gve: Fix XDP TX completion handling when counters overflow

[Praveen Kaligineedi]

From: Joshua Washington <joshwash@google.com>

In gve_clean_xdp_done, the driver processes the TX completions based on
a 32-bit NIC counter and a 32-bit completion counter stored in the tx
queue.

Fix the for loop so that the counter wraparound is handled correctly.

Fixes: 75eaae158b1b ("gve: Add XDP DROP and TX support for GQI-QPL format")
Signed-off-by: Joshua Washington <joshwash@google.com>
Signed-off-by: Praveen Kaligineedi <pkaligineedi@google.com>
---
 drivers/net/ethernet/google/gve/gve_tx.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve_tx.c b/drivers/net/ethernet/google/gve/gve_tx.c
index 24a64ec1073e..e7fb7d6d283d 100644
--- a/drivers/net/ethernet/google/gve/gve_tx.c
+++ b/drivers/net/ethernet/google/gve/gve_tx.c
@@ -158,15 +158,16 @@ static int gve_clean_xdp_done(struct gve_priv *priv, struct gve_tx_ring *tx,
 			      u32 to_do)
 {
 	struct gve_tx_buffer_state *info;
-	u32 clean_end = tx->done + to_do;
 	u64 pkts = 0, bytes = 0;
 	size_t space_freed = 0;
 	u32 xsk_complete = 0;
 	u32 idx;
+	int i;
 
-	for (; tx->done < clean_end; tx->done++) {
+	for (i = 0; i < to_do; i++) {
 		idx = tx->done & tx->mask;
 		info = &tx->info[idx];
+		tx->done++;
 
 		if (unlikely(!info->xdp.size))
 			continue;
-- 
2.45.2.803.g4e1b14247a-goog

Re: [PATCH net] gve: Fix XDP TX completion handling when counters overflow

[Simon Horman]

On Tue, Jul 16, 2024 at 10:10:41AM -0700, Praveen Kaligineedi wrote:
> From: Joshua Washington <joshwash@google.com>
> 
> In gve_clean_xdp_done, the driver processes the TX completions based on
> a 32-bit NIC counter and a 32-bit completion counter stored in the tx
> queue.
> 
> Fix the for loop so that the counter wraparound is handled correctly.
> 
> Fixes: 75eaae158b1b ("gve: Add XDP DROP and TX support for GQI-QPL format")
> Signed-off-by: Joshua Washington <joshwash@google.com>
> Signed-off-by: Praveen Kaligineedi <pkaligineedi@google.com>

Reviewed-by: Simon Horman <horms@kernel.org>

> ---
>  drivers/net/ethernet/google/gve/gve_tx.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/google/gve/gve_tx.c b/drivers/net/ethernet/google/gve/gve_tx.c
> index 24a64ec1073e..e7fb7d6d283d 100644
> --- a/drivers/net/ethernet/google/gve/gve_tx.c
> +++ b/drivers/net/ethernet/google/gve/gve_tx.c
> @@ -158,15 +158,16 @@ static int gve_clean_xdp_done(struct gve_priv *priv, struct gve_tx_ring *tx,
>  			      u32 to_do)
>  {
>  	struct gve_tx_buffer_state *info;
> -	u32 clean_end = tx->done + to_do;
>  	u64 pkts = 0, bytes = 0;
>  	size_t space_freed = 0;
>  	u32 xsk_complete = 0;
>  	u32 idx;
> +	int i;
>  
> -	for (; tx->done < clean_end; tx->done++) {
> +	for (i = 0; i < to_do; i++) {

I was slightly concerned that, as it is a u32, the value of to_do could
exceed the maximum value of i, which is an int.

But I see that in practice the value of to_do is bound by an int, budget,
in the call site, gve_xdp_poll. So I think we are ok.

Perhaps, as a clean up, the type of the to_do parameter of
gve_clean_xdp_done, and local variable in gve_xdp_poll() could be updated
from u32 to int. But, OTOH, perhaps that doesn't get us anywhere.

>  		idx = tx->done & tx->mask;
>  		info = &tx->info[idx];
> +		tx->done++;
>  
>  		if (unlikely(!info->xdp.size))
>  			continue;
> -- 
> 2.45.2.803.g4e1b14247a-goog
> 
> 

Re: [PATCH net] gve: Fix XDP TX completion handling when counters overflow

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue, 16 Jul 2024 10:10:41 -0700 you wrote:
> From: Joshua Washington <joshwash@google.com>
> 
> In gve_clean_xdp_done, the driver processes the TX completions based on
> a 32-bit NIC counter and a 32-bit completion counter stored in the tx
> queue.
> 
> Fix the for loop so that the counter wraparound is handled correctly.
> 
> [...]

Here is the summary with links:
  - [net] gve: Fix XDP TX completion handling when counters overflow
    https://git.kernel.org/netdev/net/c/03b54bad26f3

You are awesome, thank you!
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