RE: [PATCH v7 3/4] riscv: Add checksum library

[Wang, Xiao W]

Hi,

> -----Original Message-----
> From: linux-riscv <linux-riscv-bounces@xxxxxxxxxxxxxxxxxxx> On Behalf Of
> Charlie Jenkins
> Sent: Wednesday, September 20, 2023 2:45 AM
> To: Charlie Jenkins <charlie@xxxxxxxxxxxx>; Palmer Dabbelt
> <palmer@xxxxxxxxxxx>; Conor Dooley <conor@xxxxxxxxxx>; Samuel Holland
> <samuel.holland@xxxxxxxxxx>; David Laight <David.Laight@xxxxxxxxxx>;
> linux-riscv@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
> arch@xxxxxxxxxxxxxxx
> Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>; Albert Ou
> <aou@xxxxxxxxxxxxxxxxx>; Arnd Bergmann <arnd@xxxxxxxx>
> Subject: [PATCH v7 3/4] riscv: Add checksum library
> 
> Provide a 32 and 64 bit version of do_csum. When compiled for 32-bit
> will load from the buffer in groups of 32 bits, and when compiled for
> 64-bit will load in groups of 64 bits.
> 
> Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
> ---
>  arch/riscv/include/asm/checksum.h |  12 +++
>  arch/riscv/lib/Makefile           |   1 +
>  arch/riscv/lib/csum.c             | 217
> ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 230 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/checksum.h
> b/arch/riscv/include/asm/checksum.h
> index dc0dd89f2a13..7fcd07edb8b3 100644
> --- a/arch/riscv/include/asm/checksum.h
> +++ b/arch/riscv/include/asm/checksum.h
> @@ -12,6 +12,18 @@
> 
>  #define ip_fast_csum ip_fast_csum
> 
> +extern unsigned int do_csum(const unsigned char *buff, int len);
> +#define do_csum do_csum
> +
> +/* Default version is sufficient for 32 bit */
> +#ifdef CONFIG_64BIT
> +#define _HAVE_ARCH_IPV6_CSUM
> +__sum16 csum_ipv6_magic(const struct in6_addr *saddr,
> +			const struct in6_addr *daddr,
> +			__u32 len, __u8 proto, __wsum sum);
> +#endif
> +
> +// Define riscv versions of functions before importing asm-
> generic/checksum.h
>  #include <asm-generic/checksum.h>
> 
>  /*
> diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
> index 26cb2502ecf8..2aa1a4ad361f 100644
> --- a/arch/riscv/lib/Makefile
> +++ b/arch/riscv/lib/Makefile
> @@ -6,6 +6,7 @@ lib-y			+= memmove.o
>  lib-y			+= strcmp.o
>  lib-y			+= strlen.o
>  lib-y			+= strncmp.o
> +lib-y			+= csum.o
>  lib-$(CONFIG_MMU)	+= uaccess.o
>  lib-$(CONFIG_64BIT)	+= tishift.o
>  lib-$(CONFIG_RISCV_ISA_ZICBOZ)	+= clear_page.o
> diff --git a/arch/riscv/lib/csum.c b/arch/riscv/lib/csum.c
> new file mode 100644
> index 000000000000..d8fc94bff602
> --- /dev/null
> +++ b/arch/riscv/lib/csum.c
> @@ -0,0 +1,217 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * IP checksum library
> + *
> + * Influenced by arch/arm64/lib/csum.c
> + * Copyright (C) 2023 Rivos Inc.
> + */
> +#include <linux/bitops.h>
> +#include <linux/compiler.h>
> +#include <linux/kasan-checks.h>
> +#include <linux/kernel.h>
> +
> +#include <net/checksum.h>
> +
> +/* Default version is sufficient for 32 bit */

[...]
> +
> +#ifdef CONFIG_32BIT
> +#define OFFSET_MASK 3
> +#elif CONFIG_64BIT
> +#define OFFSET_MASK 7
> +#endif
> +
> +/*
> + * Perform a checksum on an arbitrary memory address.
> + * Algorithm accounts for buff being misaligned.
> + * If buff is not aligned, will over-read bytes but not use the bytes that it
> + * shouldn't. The same thing will occur on the tail-end of the read.
> + */
> +unsigned int __no_sanitize_address do_csum(const unsigned char *buff, int
> len)
> +{
> +	unsigned int offset, shift;
> +	unsigned long csum = 0, carry = 0, data;
> +	const unsigned long *ptr, *end;
> +
> +	if (unlikely(len <= 0))
> +		return 0;
> +
> +	end = (const unsigned long *)(buff + len);
> +
> +	/*
> +	 * Align address to closest word (double word on rv64) that comes
> before
> +	 * buff. This should always be in the same page and cache line.
> +	 * Directly call KASAN with the alignment we will be using.
> +	 */
> +	offset = (unsigned long)buff & OFFSET_MASK;
> +	kasan_check_read(buff, len);
> +	ptr = (const unsigned long *)(buff - offset);
> +
> +	/*
> +	 * Clear the most significant bytes that were over-read if buff was not
> +	 * aligned.
> +	 */
> +	shift = offset * 8;
> +	data = *(ptr++);
> +#ifdef __LITTLE_ENDIAN
> +	data = (data >> shift) << shift;
> +#else
> +	data = (data << shift) >> shift;
> +#endif
> +	/*
> +	 * Do 32-bit reads on RV32 and 64-bit reads otherwise. This should be
> +	 * faster than doing 32-bit reads on architectures that support larger
> +	 * reads.
> +	 */
> +	while (ptr < end) {
> +		csum += data;
> +		carry += csum < data;
> +		len -= sizeof(long);
> +		data = *(ptr++);
> +	}
> +
> +	/*
> +	 * Perform alignment (and over-read) bytes on the tail if any bytes
> +	 * leftover.
> +	 */
> +	shift = ((long)ptr - (long)end) * 8;
> +#ifdef __LITTLE_ENDIAN
> +	data = (data << shift) >> shift;
> +#else
> +	data = (data >> shift) << shift;
> +#endif
> +	csum += data;
> +	carry += csum < data;
> +	csum += carry;
> +	csum += csum < carry;
> +
> +	/*
> +	 * Zbb support saves 6 instructions, so not worth checking without
> +	 * alternatives if supported
> +	 */
> +	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
> +	    IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> +		unsigned long fold_temp;
> +
> +		/*
> +		 * Zbb is likely available when the kernel is compiled with Zbb
> +		 * support, so nop when Zbb is available and jump when Zbb
> is
> +		 * not available.
> +		 */
> +		asm_volatile_goto(ALTERNATIVE("j %l[no_zbb]", "nop", 0,
> +					      RISCV_ISA_EXT_ZBB, 1)
> +				  :
> +				  :
> +				  :
> +				  : no_zbb);
> +
> +#ifdef CONFIG_32BIT
> +		asm_volatile_goto(".option push			\n\
> +		.option arch,+zbb				\n\
> +			rori	%[fold_temp], %[csum], 16	\n\
> +			andi	%[offset], %[offset], 1		\n\
> +			add	%[csum], %[fold_temp], %[csum]	\n\
> +			beq	%[offset], zero, %l[end]	\n\
> +			rev8	%[csum], %[csum]		\n\
> +		.option pop"
> +			: [csum] "+r" (csum),
> +				[fold_temp] "=&r" (fold_temp)

Seems no need to add extra indent for this line, and the same comment for the below 64Bit case.

BRs,
Xiao

> +			: [offset] "r" (offset)
> +			:
> +			: end);
> +
> +		return (unsigned short)csum;
> +#else // !CONFIG_32BIT
> +		asm_volatile_goto(".option push			\n\
> +		.option arch,+zbb				\n\
> +			rori	%[fold_temp], %[csum], 32	\n\
> +			add	%[csum], %[fold_temp], %[csum]	\n\
> +			srli	%[csum], %[csum], 32		\n\
> +			roriw	%[fold_temp], %[csum], 16	\n\
> +			addw	%[csum], %[fold_temp], %[csum]	\n\
> +			andi	%[offset], %[offset], 1		\n\
> +			beq	%[offset], zero, %l[end]	\n\
> +			rev8	%[csum], %[csum]		\n\
> +		.option pop"
> +			: [csum] "+r" (csum),
> +				[fold_temp] "=&r" (fold_temp)
> +			: [offset] "r" (offset)
> +			:
> +			: end);
> +
> +		return (csum << 16) >> 48;
> +#endif // !CONFIG_32BIT
> +end:
> +		return csum >> 16;
> +	}
> +no_zbb:
> +#ifndef CONFIG_32BIT
> +	csum += ror64(csum, 32);
> +	csum >>= 32;
> +#endif
> +	csum = (u32)csum + ror32((u32)csum, 16);
> +	if (offset & 1)
> +		return (u16)swab32(csum);
> +	return csum >> 16;
> +}
> 
> --
> 2.42.0
> 
> 
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