diff mbox series

[net-next,v2,6/6] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum header

Message ID 20210306031550.26530-7-elder@linaro.org
State Superseded
Headers show
Series net: qualcomm: rmnet: stop using C bit-fields | expand

Commit Message

Alex Elder March 6, 2021, 3:15 a.m. UTC 
Replace the use of C bit-fields in the rmnet_map_ul_csum_header
structure with a single two-byte (big endian) structure member,
and use field masks to encode or get values within it.

Previously rmnet_map_ipv4_ul_csum_header() would update values in
the host byte-order fields, and then forcibly fix their byte order
using a combination of byte order operations and types.

Instead, just compute the value that needs to go into the new
structure member and save it with a simple byte-order conversion.

Make similar simplifications in rmnet_map_ipv6_ul_csum_header().

Finally, in rmnet_map_checksum_uplink_packet() a set of assignments
zeroes every field in the upload checksum header.  Replace that with
a single memset() operation.

Signed-off-by: Alex Elder <elder@linaro.org>

Reported-by: kernel test robot <lkp@intel.com>
---
v2: Fixed to use u16_encode_bits() instead of be16_encode_bits().

 .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 34 ++++++-------------
 include/linux/if_rmnet.h                      | 21 ++++++------
 2 files changed, 21 insertions(+), 34 deletions(-)

-- 
2.27.0

Comments

David Laight March 8, 2021, 10:18 a.m. UTC | #1 
From: Alex Elder

> Sent: 06 March 2021 03:16

> 

> Replace the use of C bit-fields in the rmnet_map_ul_csum_header

> structure with a single two-byte (big endian) structure member,

> and use field masks to encode or get values within it.

> 

> Previously rmnet_map_ipv4_ul_csum_header() would update values in

> the host byte-order fields, and then forcibly fix their byte order

> using a combination of byte order operations and types.

> 

> Instead, just compute the value that needs to go into the new

> structure member and save it with a simple byte-order conversion.

> 

> Make similar simplifications in rmnet_map_ipv6_ul_csum_header().

> 

> Finally, in rmnet_map_checksum_uplink_packet() a set of assignments

> zeroes every field in the upload checksum header.  Replace that with

> a single memset() operation.

> 

> Signed-off-by: Alex Elder <elder@linaro.org>

> Reported-by: kernel test robot <lkp@intel.com>

> ---

> v2: Fixed to use u16_encode_bits() instead of be16_encode_bits().

> 

>  .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 34 ++++++-------------

>  include/linux/if_rmnet.h                      | 21 ++++++------

>  2 files changed, 21 insertions(+), 34 deletions(-)

> 

> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c

> b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c

> index 29d485b868a65..b76ad48da7325 100644

> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c

> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c

> @@ -198,23 +198,19 @@ rmnet_map_ipv4_ul_csum_header(void *iphdr,

>  			      struct rmnet_map_ul_csum_header *ul_header,

>  			      struct sk_buff *skb)

>  {

> -	__be16 *hdr = (__be16 *)ul_header;

>  	struct iphdr *ip4h = iphdr;

>  	u16 offset;

> +	u16 val;

> 

>  	offset = skb_transport_header(skb) - (unsigned char *)iphdr;

>  	ul_header->csum_start_offset = htons(offset);

> 

> -	ul_header->csum_insert_offset = skb->csum_offset;

> -	ul_header->csum_enabled = 1;

> +	val = u16_encode_bits(1, MAP_CSUM_UL_ENABLED_FMASK);

>  	if (ip4h->protocol == IPPROTO_UDP)

> -		ul_header->udp_ind = 1;

> -	else

> -		ul_header->udp_ind = 0;

> +		val |= u16_encode_bits(1, MAP_CSUM_UL_UDP_FMASK);

> +	val |= u16_encode_bits(skb->csum_offset, MAP_CSUM_UL_OFFSET_FMASK);

> 

> -	/* Changing remaining fields to network order */

> -	hdr++;

> -	*hdr = htons((__force u16)*hdr);

> +	ul_header->csum_info = htons(val);


Isn't this potentially misaligned?

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
Alex Elder March 8, 2021, 1:59 p.m. UTC | #2 
On 3/8/21 4:18 AM, David Laight wrote:
> From: Alex Elder

>> Sent: 06 March 2021 03:16

>>

>> Replace the use of C bit-fields in the rmnet_map_ul_csum_header

>> structure with a single two-byte (big endian) structure member,

>> and use field masks to encode or get values within it.

>>

>> Previously rmnet_map_ipv4_ul_csum_header() would update values in

>> the host byte-order fields, and then forcibly fix their byte order

>> using a combination of byte order operations and types.

>>

>> Instead, just compute the value that needs to go into the new

>> structure member and save it with a simple byte-order conversion.

>>

>> Make similar simplifications in rmnet_map_ipv6_ul_csum_header().

>>

>> Finally, in rmnet_map_checksum_uplink_packet() a set of assignments

>> zeroes every field in the upload checksum header.  Replace that with

>> a single memset() operation.

>>

>> Signed-off-by: Alex Elder <elder@linaro.org>

>> Reported-by: kernel test robot <lkp@intel.com>

>> ---

>> v2: Fixed to use u16_encode_bits() instead of be16_encode_bits().

>>

>>   .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 34 ++++++-------------

>>   include/linux/if_rmnet.h                      | 21 ++++++------

>>   2 files changed, 21 insertions(+), 34 deletions(-)

>>

>> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c

>> b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c

>> index 29d485b868a65..b76ad48da7325 100644

>> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c

>> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c

>> @@ -198,23 +198,19 @@ rmnet_map_ipv4_ul_csum_header(void *iphdr,

>>   			      struct rmnet_map_ul_csum_header *ul_header,

>>   			      struct sk_buff *skb)

>>   {

>> -	__be16 *hdr = (__be16 *)ul_header;

>>   	struct iphdr *ip4h = iphdr;

>>   	u16 offset;

>> +	u16 val;

>>

>>   	offset = skb_transport_header(skb) - (unsigned char *)iphdr;

>>   	ul_header->csum_start_offset = htons(offset);

>>

>> -	ul_header->csum_insert_offset = skb->csum_offset;

>> -	ul_header->csum_enabled = 1;

>> +	val = u16_encode_bits(1, MAP_CSUM_UL_ENABLED_FMASK);

>>   	if (ip4h->protocol == IPPROTO_UDP)

>> -		ul_header->udp_ind = 1;

>> -	else

>> -		ul_header->udp_ind = 0;

>> +		val |= u16_encode_bits(1, MAP_CSUM_UL_UDP_FMASK);

>> +	val |= u16_encode_bits(skb->csum_offset, MAP_CSUM_UL_OFFSET_FMASK);

>>

>> -	/* Changing remaining fields to network order */

>> -	hdr++;

>> -	*hdr = htons((__force u16)*hdr);

>> +	ul_header->csum_info = htons(val);

> 

> Isn't this potentially misaligned?


At first I thought you were talking about column alignment.

The short answer:  Yes (at least it's possible)!  And
that's a problem elsewhere in the driver.  I noticed
that before and confirmed that unaligned accesses *do*
occur in this driver.

I would want to fix that comprehensively (and separate
from this patch), and not just in this one spot.  I have
not done it because I am not set up to readily test the
change; unaligned access does not cause a fault on aarch64
(or at least on the platforms I'm using).

Sort of related, I have been meaning to eliminate the
pointless __aligned(1) tags on rmnet structures defined
in <linux/if_rmnet.h>.  It wouldn't hurt to use __packed,
though I think they're all 4 or 8 bytes naturally anyway.
Perhaps marking them __aligned(4) would help identify
potential unaligned accesses?

Anyway, assuming you're not talking about tab stops, yes
it's possible this assignment is misaligned.  But it's a
bigger problem than what you point out.  I will take this
as a sign that I'm not the only one who has this concern,
meaning I should maybe bump the priority on getting this
alignment thing fixed.

					-Alex

> 

> 	David

> 

> -

> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK

> Registration No: 1397386 (Wales)

>
David Laight March 8, 2021, 2:10 p.m. UTC | #3 
...
> Sort of related, I have been meaning to eliminate the

> pointless __aligned(1) tags on rmnet structures defined

> in <linux/if_rmnet.h>.  It wouldn't hurt to use __packed,

> though I think they're all 4 or 8 bytes naturally anyway.

> Perhaps marking them __aligned(4) would help identify

> potential unaligned accesses?


Don't use __packed (etc) unless the data might be misaligned.
If the architecture doesn't support misaligned memory
accesses then the compiler has to generate code that
does byte accesses and shifts.

__aligned(4) is mostly useful for structures that have
to have an 8-byte field on a 4-byte boundary.
(As happens in the x86 compat32 code.)

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
diff mbox series

Patch

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
index 29d485b868a65..b76ad48da7325 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -198,23 +198,19 @@  rmnet_map_ipv4_ul_csum_header(void *iphdr,
 			      struct rmnet_map_ul_csum_header *ul_header,
 			      struct sk_buff *skb)
 {
-	__be16 *hdr = (__be16 *)ul_header;
 	struct iphdr *ip4h = iphdr;
 	u16 offset;
+	u16 val;
 
 	offset = skb_transport_header(skb) - (unsigned char *)iphdr;
 	ul_header->csum_start_offset = htons(offset);
 
-	ul_header->csum_insert_offset = skb->csum_offset;
-	ul_header->csum_enabled = 1;
+	val = u16_encode_bits(1, MAP_CSUM_UL_ENABLED_FMASK);
 	if (ip4h->protocol == IPPROTO_UDP)
-		ul_header->udp_ind = 1;
-	else
-		ul_header->udp_ind = 0;
+		val |= u16_encode_bits(1, MAP_CSUM_UL_UDP_FMASK);
+	val |= u16_encode_bits(skb->csum_offset, MAP_CSUM_UL_OFFSET_FMASK);
 
-	/* Changing remaining fields to network order */
-	hdr++;
-	*hdr = htons((__force u16)*hdr);
+	ul_header->csum_info = htons(val);
 
 	skb->ip_summed = CHECKSUM_NONE;
 
@@ -241,24 +237,19 @@  rmnet_map_ipv6_ul_csum_header(void *ip6hdr,
 			      struct rmnet_map_ul_csum_header *ul_header,
 			      struct sk_buff *skb)
 {
-	__be16 *hdr = (__be16 *)ul_header;
 	struct ipv6hdr *ip6h = ip6hdr;
 	u16 offset;
+	u16 val;
 
 	offset = skb_transport_header(skb) - (unsigned char *)ip6hdr;
 	ul_header->csum_start_offset = htons(offset);
 
-	ul_header->csum_insert_offset = skb->csum_offset;
-	ul_header->csum_enabled = 1;
-
+	val = u16_encode_bits(1, MAP_CSUM_UL_ENABLED_FMASK);
 	if (ip6h->nexthdr == IPPROTO_UDP)
-		ul_header->udp_ind = 1;
-	else
-		ul_header->udp_ind = 0;
+		val |= u16_encode_bits(1, MAP_CSUM_UL_UDP_FMASK);
+	val |= u16_encode_bits(skb->csum_offset, MAP_CSUM_UL_OFFSET_FMASK);
 
-	/* Changing remaining fields to network order */
-	hdr++;
-	*hdr = htons((__force u16)*hdr);
+	ul_header->csum_info = htons(val);
 
 	skb->ip_summed = CHECKSUM_NONE;
 
@@ -425,10 +416,7 @@  void rmnet_map_checksum_uplink_packet(struct sk_buff *skb,
 	}
 
 sw_csum:
-	ul_header->csum_start_offset = 0;
-	ul_header->csum_insert_offset = 0;
-	ul_header->csum_enabled = 0;
-	ul_header->udp_ind = 0;
+	memset(ul_header, 0, sizeof(*ul_header));
 
 	priv->stats.csum_sw++;
 }
diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
index 1fbb7531238b6..9ff09a2bcf9e1 100644
--- a/include/linux/if_rmnet.h
+++ b/include/linux/if_rmnet.h
@@ -33,17 +33,16 @@  struct rmnet_map_dl_csum_trailer {
 
 struct rmnet_map_ul_csum_header {
 	__be16 csum_start_offset;
-#if defined(__LITTLE_ENDIAN_BITFIELD)
-	u16 csum_insert_offset:14;
-	u16 udp_ind:1;
-	u16 csum_enabled:1;
-#elif defined (__BIG_ENDIAN_BITFIELD)
-	u16 csum_enabled:1;
-	u16 udp_ind:1;
-	u16 csum_insert_offset:14;
-#else
-#error	"Please fix <asm/byteorder.h>"
-#endif
+	__be16 csum_info;		/* MAP_CSUM_UL_*_FMASK */
 } __aligned(1);
 
+/* csum_info field:
+ *  OFFSET:	where (offset in bytes) to insert computed checksum
+ *  UDP:	1 = UDP checksum (zero checkum means no checksum)
+ *  ENABLED:	1 = checksum computation requested
+ */
+#define MAP_CSUM_UL_OFFSET_FMASK	GENMASK(13, 0)
+#define MAP_CSUM_UL_UDP_FMASK		GENMASK(14, 14)
+#define MAP_CSUM_UL_ENABLED_FMASK	GENMASK(15, 15)
+
 #endif /* !(_LINUX_IF_RMNET_H_) */