[v7,2/4] riscv: Checksum header

  Provide checksum algorithms that have been designed to leverage riscv
instructions such as rotate. In 64-bit, can take advantage of the larger
register to avoid some overflow checking.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
---
 arch/riscv/include/asm/checksum.h | 79 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
  

On Tue, Sep 19, 2023 at 11:44:31AM -0700, Charlie Jenkins wrote:
> Provide checksum algorithms that have been designed to leverage riscv
> instructions such as rotate. In 64-bit, can take advantage of the larger
> register to avoid some overflow checking.
> 
> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>

Same here,
Acked-by: Conor Dooley <conor.dooley@microchip.com>

I think there are some "issues" attributed to this patch by the
automation - but they spurious. This diff here could not cause a
drivers/block/drbd/drbd_bitmap.c:1271: warning: Function parameter or member 'peer_device' not described in 'drbd_bm_write_copy_pages'
after all.

Cheers,
Conor.

> ---
>  arch/riscv/include/asm/checksum.h | 79 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 79 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/checksum.h b/arch/riscv/include/asm/checksum.h
> new file mode 100644
> index 000000000000..dc0dd89f2a13
> --- /dev/null
> +++ b/arch/riscv/include/asm/checksum.h
> @@ -0,0 +1,79 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * IP checksum routines
> + *
> + * Copyright (C) 2023 Rivos Inc.
> + */
> +#ifndef __ASM_RISCV_CHECKSUM_H
> +#define __ASM_RISCV_CHECKSUM_H
> +
> +#include <linux/in6.h>
> +#include <linux/uaccess.h>
> +
> +#define ip_fast_csum ip_fast_csum
> +
> +#include <asm-generic/checksum.h>
> +
> +/*
> + * Quickly compute an IP checksum with the assumption that IPv4 headers will
> + * always be in multiples of 32-bits, and have an ihl of at least 5.
> + * @ihl is the number of 32 bit segments and must be greater than or equal to 5.
> + * @iph is assumed to be word aligned.
> + */
> +static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
> +{
> +	unsigned long csum = 0;
> +	int pos = 0;
> +
> +	do {
> +		csum += ((const unsigned int *)iph)[pos];
> +		if (IS_ENABLED(CONFIG_32BIT))
> +			csum += csum < ((const unsigned int *)iph)[pos];
> +	} while (++pos < ihl);
> +
> +	/*
> +	 * ZBB only saves three instructions on 32-bit and five on 64-bit so not
> +	 * worth checking if supported without Alternatives.
> +	 */
> +	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
> +	    IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> +		unsigned long fold_temp;
> +
> +		asm_volatile_goto(ALTERNATIVE("j %l[no_zbb]", "nop", 0,
> +					      RISCV_ISA_EXT_ZBB, 1)
> +		    :
> +		    :
> +		    :
> +		    : no_zbb);
> +
> +		if (IS_ENABLED(CONFIG_32BIT)) {
> +			asm(".option push				\n\
> +			.option arch,+zbb				\n\
> +				not	%[fold_temp], %[csum]		\n\
> +				rori	%[csum], %[csum], 16		\n\
> +				sub	%[csum], %[fold_temp], %[csum]	\n\
> +			.option pop"
> +			: [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp));
> +		} else {
> +			asm(".option push				\n\
> +			.option arch,+zbb				\n\
> +				rori	%[fold_temp], %[csum], 32	\n\
> +				add	%[csum], %[fold_temp], %[csum]	\n\
> +				srli	%[csum], %[csum], 32		\n\
> +				not	%[fold_temp], %[csum]		\n\
> +				roriw	%[csum], %[csum], 16		\n\
> +				subw	%[csum], %[fold_temp], %[csum]	\n\
> +			.option pop"
> +			: [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp));
> +		}
> +		return csum >> 16;
> +	}
> +no_zbb:
> +#ifndef CONFIG_32BIT
> +	csum += (csum >> 32) | (csum << 32);
> +	csum >>= 32;
> +#endif
> +	return csum_fold((__force __wsum)csum);
> +}
> +
> +#endif // __ASM_RISCV_CHECKSUM_H
> 
> -- 
> 2.42.0
>
  

Hi Charlie,

> -----Original Message-----
> From: linux-riscv <linux-riscv-bounces@lists.infradead.org> On Behalf Of
> Charlie Jenkins
> Sent: Wednesday, September 20, 2023 2:45 AM
> To: Charlie Jenkins <charlie@rivosinc.com>; Palmer Dabbelt
> <palmer@dabbelt.com>; Conor Dooley <conor@kernel.org>; Samuel Holland
> <samuel.holland@sifive.com>; David Laight <David.Laight@aculab.com>;
> linux-riscv@lists.infradead.org; linux-kernel@vger.kernel.org; linux-
> arch@vger.kernel.org
> Cc: Paul Walmsley <paul.walmsley@sifive.com>; Albert Ou
> <aou@eecs.berkeley.edu>; Arnd Bergmann <arnd@arndb.de>
> Subject: [PATCH v7 2/4] riscv: Checksum header
> 
> Provide checksum algorithms that have been designed to leverage riscv
> instructions such as rotate. In 64-bit, can take advantage of the larger
> register to avoid some overflow checking.
> 
> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> ---
>  arch/riscv/include/asm/checksum.h | 79
> +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 79 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/checksum.h
> b/arch/riscv/include/asm/checksum.h
> new file mode 100644
> index 000000000000..dc0dd89f2a13
> --- /dev/null
> +++ b/arch/riscv/include/asm/checksum.h
> @@ -0,0 +1,79 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * IP checksum routines
> + *
> + * Copyright (C) 2023 Rivos Inc.
> + */
> +#ifndef __ASM_RISCV_CHECKSUM_H
> +#define __ASM_RISCV_CHECKSUM_H
> +
> +#include <linux/in6.h>
> +#include <linux/uaccess.h>
> +
> +#define ip_fast_csum ip_fast_csum
> +
> +#include <asm-generic/checksum.h>
> +
> +/*
> + * Quickly compute an IP checksum with the assumption that IPv4 headers
> will
> + * always be in multiples of 32-bits, and have an ihl of at least 5.
> + * @ihl is the number of 32 bit segments and must be greater than or equal
> to 5.
> + * @iph is assumed to be word aligned.

Not sure if the assumption is always true. It looks the implementation in "lib/checksum.c" doesn't take this assumption.
The ip header can comes after a 14-Byte ether header, which may start from a word-aligned or DMA friendly address.

> + */
> +static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
> +{
> +	unsigned long csum = 0;
> +	int pos = 0;
> +
> +	do {
> +		csum += ((const unsigned int *)iph)[pos];
> +		if (IS_ENABLED(CONFIG_32BIT))
> +			csum += csum < ((const unsigned int *)iph)[pos];
> +	} while (++pos < ihl);
> +
> +	/*
> +	 * ZBB only saves three instructions on 32-bit and five on 64-bit so not
> +	 * worth checking if supported without Alternatives.
> +	 */
> +	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
> +	    IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> +		unsigned long fold_temp;
> +
> +		asm_volatile_goto(ALTERNATIVE("j %l[no_zbb]", "nop", 0,
> +					      RISCV_ISA_EXT_ZBB, 1)
> +		    :
> +		    :
> +		    :
> +		    : no_zbb);
> +
> +		if (IS_ENABLED(CONFIG_32BIT)) {
> +			asm(".option push				\n\
> +			.option arch,+zbb				\n\
> +				not	%[fold_temp], %[csum]
> 	\n\
> +				rori	%[csum], %[csum], 16		\n\
> +				sub	%[csum], %[fold_temp], %[csum]
> 	\n\
> +			.option pop"
> +			: [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp));
> +		} else {
> +			asm(".option push				\n\
> +			.option arch,+zbb				\n\
> +				rori	%[fold_temp], %[csum], 32	\n\
> +				add	%[csum], %[fold_temp], %[csum]
> 	\n\
> +				srli	%[csum], %[csum], 32		\n\
> +				not	%[fold_temp], %[csum]
> 	\n\
> +				roriw	%[csum], %[csum], 16		\n\
> +				subw	%[csum], %[fold_temp], %[csum]
> 	\n\
> +			.option pop"
> +			: [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp));
> +		}
> +		return csum >> 16;
> +	}
> +no_zbb:
> +#ifndef CONFIG_32BIT
> +	csum += (csum >> 32) | (csum << 32);

Just like patch 3/4 does, we can call ror64(csum, 32).

BRs,
Xiao

> +	csum >>= 32;
> +#endif
> +	return csum_fold((__force __wsum)csum);
> +}
> +
> +#endif // __ASM_RISCV_CHECKSUM_H
> 
> --
> 2.42.0
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
  

On Wed, Oct 25, 2023 at 06:50:05AM +0000, Wang, Xiao W wrote:
> Hi Charlie,
> 
> > -----Original Message-----
> > From: linux-riscv <linux-riscv-bounces@lists.infradead.org> On Behalf Of
> > Charlie Jenkins
> > Sent: Wednesday, September 20, 2023 2:45 AM
> > To: Charlie Jenkins <charlie@rivosinc.com>; Palmer Dabbelt
> > <palmer@dabbelt.com>; Conor Dooley <conor@kernel.org>; Samuel Holland
> > <samuel.holland@sifive.com>; David Laight <David.Laight@aculab.com>;
> > linux-riscv@lists.infradead.org; linux-kernel@vger.kernel.org; linux-
> > arch@vger.kernel.org
> > Cc: Paul Walmsley <paul.walmsley@sifive.com>; Albert Ou
> > <aou@eecs.berkeley.edu>; Arnd Bergmann <arnd@arndb.de>
> > Subject: [PATCH v7 2/4] riscv: Checksum header
> > 
> > Provide checksum algorithms that have been designed to leverage riscv
> > instructions such as rotate. In 64-bit, can take advantage of the larger
> > register to avoid some overflow checking.
> > 
> > Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> > ---
> >  arch/riscv/include/asm/checksum.h | 79
> > +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 79 insertions(+)
> > 
> > diff --git a/arch/riscv/include/asm/checksum.h
> > b/arch/riscv/include/asm/checksum.h
> > new file mode 100644
> > index 000000000000..dc0dd89f2a13
> > --- /dev/null
> > +++ b/arch/riscv/include/asm/checksum.h
> > @@ -0,0 +1,79 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * IP checksum routines
> > + *
> > + * Copyright (C) 2023 Rivos Inc.
> > + */
> > +#ifndef __ASM_RISCV_CHECKSUM_H
> > +#define __ASM_RISCV_CHECKSUM_H
> > +
> > +#include <linux/in6.h>
> > +#include <linux/uaccess.h>
> > +
> > +#define ip_fast_csum ip_fast_csum
> > +
> > +#include <asm-generic/checksum.h>
> > +
> > +/*
> > + * Quickly compute an IP checksum with the assumption that IPv4 headers
> > will
> > + * always be in multiples of 32-bits, and have an ihl of at least 5.
> > + * @ihl is the number of 32 bit segments and must be greater than or equal
> > to 5.
> > + * @iph is assumed to be word aligned.
> 
> Not sure if the assumption is always true. It looks the implementation in "lib/checksum.c" doesn't take this assumption.
> The ip header can comes after a 14-Byte ether header, which may start from a word-aligned or DMA friendly address.

While lib/checksum.c does not make this assumption, other architectures
(x86, ARM, powerpc, mips, arc) do make this assumption. Architectures
seem to only align the header on a word boundary in do_csum. I worry
that the benefit of aligning iph in this "fast" csum function would
disproportionately impact hardware that has fast misaligned accesses.

- Charlie

> 
> > + */
> > +static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
> > +{
> > +	unsigned long csum = 0;
> > +	int pos = 0;
> > +
> > +	do {
> > +		csum += ((const unsigned int *)iph)[pos];
> > +		if (IS_ENABLED(CONFIG_32BIT))
> > +			csum += csum < ((const unsigned int *)iph)[pos];
> > +	} while (++pos < ihl);
> > +
> > +	/*
> > +	 * ZBB only saves three instructions on 32-bit and five on 64-bit so not
> > +	 * worth checking if supported without Alternatives.
> > +	 */
> > +	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
> > +	    IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> > +		unsigned long fold_temp;
> > +
> > +		asm_volatile_goto(ALTERNATIVE("j %l[no_zbb]", "nop", 0,
> > +					      RISCV_ISA_EXT_ZBB, 1)
> > +		    :
> > +		    :
> > +		    :
> > +		    : no_zbb);
> > +
> > +		if (IS_ENABLED(CONFIG_32BIT)) {
> > +			asm(".option push				\n\
> > +			.option arch,+zbb				\n\
> > +				not	%[fold_temp], %[csum]
> > 	\n\
> > +				rori	%[csum], %[csum], 16		\n\
> > +				sub	%[csum], %[fold_temp], %[csum]
> > 	\n\
> > +			.option pop"
> > +			: [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp));
> > +		} else {
> > +			asm(".option push				\n\
> > +			.option arch,+zbb				\n\
> > +				rori	%[fold_temp], %[csum], 32	\n\
> > +				add	%[csum], %[fold_temp], %[csum]
> > 	\n\
> > +				srli	%[csum], %[csum], 32		\n\
> > +				not	%[fold_temp], %[csum]
> > 	\n\
> > +				roriw	%[csum], %[csum], 16		\n\
> > +				subw	%[csum], %[fold_temp], %[csum]
> > 	\n\
> > +			.option pop"
> > +			: [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp));
> > +		}
> > +		return csum >> 16;
> > +	}
> > +no_zbb:
> > +#ifndef CONFIG_32BIT
> > +	csum += (csum >> 32) | (csum << 32);
> 
> Just like patch 3/4 does, we can call ror64(csum, 32).
> 
> BRs,
> Xiao
> 
> > +	csum >>= 32;
> > +#endif
> > +	return csum_fold((__force __wsum)csum);
> > +}
> > +
> > +#endif // __ASM_RISCV_CHECKSUM_H
> > 
> > --
> > 2.42.0
> > 
> > 
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
  

On Wed, Oct 25, 2023, at 22:37, Charlie Jenkins wrote:
> On Wed, Oct 25, 2023 at 06:50:05AM +0000, Wang, Xiao W wrote:

>> > +
>> > +/*
>> > + * Quickly compute an IP checksum with the assumption that IPv4 headers
>> > will
>> > + * always be in multiples of 32-bits, and have an ihl of at least 5.
>> > + * @ihl is the number of 32 bit segments and must be greater than or equal
>> > to 5.
>> > + * @iph is assumed to be word aligned.
>> 
>> Not sure if the assumption is always true. It looks the implementation in "lib/checksum.c" doesn't take this assumption.
>> The ip header can comes after a 14-Byte ether header, which may start from a word-aligned or DMA friendly address.
>
> While lib/checksum.c does not make this assumption, other architectures
> (x86, ARM, powerpc, mips, arc) do make this assumption. Architectures
> seem to only align the header on a word boundary in do_csum. I worry
> that the benefit of aligning iph in this "fast" csum function would
> disproportionately impact hardware that has fast misaligned accesses.

Most architectures set NET_IP_ALIGN to '2', which is intended
to have the IP header at a 32-bit aligned address, though
some other targets don't bother:

arch/arm64/include/asm/processor.h:#define NET_IP_ALIGN 0
arch/powerpc/include/asm/processor.h:#define NET_IP_ALIGN       0
arch/x86/include/asm/processor.h:#define NET_IP_ALIGN   0
include/linux/skbuff.h:#define NET_IP_ALIGN     2

I think it's considered a driver bug if an SKB ends up
with a misaligned IP header, but it's also something that
some of the more obscure drivers get wrong.

    Arnd
  

On Wed, Oct 25, 2023 at 10:52:22PM +0200, Arnd Bergmann wrote:
> On Wed, Oct 25, 2023, at 22:37, Charlie Jenkins wrote:
> > On Wed, Oct 25, 2023 at 06:50:05AM +0000, Wang, Xiao W wrote:
> 
> >> > +
> >> > +/*
> >> > + * Quickly compute an IP checksum with the assumption that IPv4 headers
> >> > will
> >> > + * always be in multiples of 32-bits, and have an ihl of at least 5.
> >> > + * @ihl is the number of 32 bit segments and must be greater than or equal
> >> > to 5.
> >> > + * @iph is assumed to be word aligned.
> >> 
> >> Not sure if the assumption is always true. It looks the implementation in "lib/checksum.c" doesn't take this assumption.
> >> The ip header can comes after a 14-Byte ether header, which may start from a word-aligned or DMA friendly address.
> >
> > While lib/checksum.c does not make this assumption, other architectures
> > (x86, ARM, powerpc, mips, arc) do make this assumption. Architectures
> > seem to only align the header on a word boundary in do_csum. I worry
> > that the benefit of aligning iph in this "fast" csum function would
> > disproportionately impact hardware that has fast misaligned accesses.
> 
> Most architectures set NET_IP_ALIGN to '2', which is intended
> to have the IP header at a 32-bit aligned address, though
> some other targets don't bother:
> 
> arch/arm64/include/asm/processor.h:#define NET_IP_ALIGN 0
> arch/powerpc/include/asm/processor.h:#define NET_IP_ALIGN       0
> arch/x86/include/asm/processor.h:#define NET_IP_ALIGN   0
> include/linux/skbuff.h:#define NET_IP_ALIGN     2
> 
> I think it's considered a driver bug if an SKB ends up
> with a misaligned IP header, but it's also something that
> some of the more obscure drivers get wrong.
> 
>     Arnd

Thank you for pointing that out, I had not realized that macro existed.
Since riscv keeps NET_IP_ALIGN at 0 it should be expected that
ip_fast_csum is only called with 32-bit aligned addresses. I will update
the comment and refer to that macro. riscv supports misaligned accesses
but there are no guarantees of speed.

- Charlie
  

On Wed, Oct 25, 2023, at 23:11, Charlie Jenkins wrote:
>
> Thank you for pointing that out, I had not realized that macro existed.
> Since riscv keeps NET_IP_ALIGN at 0 it should be expected that
> ip_fast_csum is only called with 32-bit aligned addresses. I will update
> the comment and refer to that macro. riscv supports misaligned accesses
> but there are no guarantees of speed.

Just to clarify for your comment: riscv gets the default value of '2',
which is the one that makes the header aligned.

      Arnd
  

On Wed, Oct 25, 2023 at 11:18:40PM +0200, Arnd Bergmann wrote:
> On Wed, Oct 25, 2023, at 23:11, Charlie Jenkins wrote:
> >
> > Thank you for pointing that out, I had not realized that macro existed.
> > Since riscv keeps NET_IP_ALIGN at 0 it should be expected that
> > ip_fast_csum is only called with 32-bit aligned addresses. I will update
> > the comment and refer to that macro. riscv supports misaligned accesses
> > but there are no guarantees of speed.
> 
> Just to clarify for your comment: riscv gets the default value of '2',
> which is the one that makes the header aligned.
> 
>       Arnd

Oops, typo. I meant to write 2.

- Charlie