[PATCH v10 4/5] riscv: Add checksum library
Wang, Xiao W
xiao.w.wang at intel.com
Tue Nov 7 00:39:54 PST 2023
> -----Original Message-----
> From: Charlie Jenkins <charlie at rivosinc.com>
> Sent: Thursday, November 2, 2023 6:48 AM
> To: Charlie Jenkins <charlie at rivosinc.com>; Palmer Dabbelt
> <palmer at dabbelt.com>; Conor Dooley <conor at kernel.org>; Samuel Holland
> <samuel.holland at sifive.com>; David Laight <David.Laight at aculab.com>;
> Wang, Xiao W <xiao.w.wang at intel.com>; Evan Green <evan at rivosinc.com>;
> linux-riscv at lists.infradead.org; linux-kernel at vger.kernel.org; linux-
> arch at vger.kernel.org
> Cc: Paul Walmsley <paul.walmsley at sifive.com>; Albert Ou
> <aou at eecs.berkeley.edu>; Arnd Bergmann <arnd at arndb.de>; Conor Dooley
> <conor.dooley at microchip.com>
> Subject: [PATCH v10 4/5] 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.
The csum_ipv6_magic() API is also provided in this patch for 64-bit , but not
mentioned in the commit log.
>
> Signed-off-by: Charlie Jenkins <charlie at rivosinc.com>
> Acked-by: Conor Dooley <conor.dooley at microchip.com>
> ---
> arch/riscv/include/asm/checksum.h | 11 ++
> arch/riscv/lib/Makefile | 1 +
> arch/riscv/lib/csum.c | 326
> ++++++++++++++++++++++++++++++++++++++
> 3 files changed, 338 insertions(+)
>
> diff --git a/arch/riscv/include/asm/checksum.h
> b/arch/riscv/include/asm/checksum.h
> index 3d77cac338fe..f8f8e437a88a 100644
> --- a/arch/riscv/include/asm/checksum.h
> +++ b/arch/riscv/include/asm/checksum.h
> @@ -12,6 +12,17 @@
>
> #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 */
> +#ifndef CONFIG_32BIT
> +#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..3221d4520bbb
> --- /dev/null
> +++ b/arch/riscv/lib/csum.c
> @@ -0,0 +1,326 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Checksum library
> + *
> + * Influenced by arch/arm64/lib/csum.c
> + * Copyright (C) 2023 Rivos Inc.
> + */
> +#include <linux/bitops.h>
> +#include <linux/compiler.h>
> +#include <asm/cpufeature.h>
It seems generally we separate the header including codes for <linux/*.h> and <asm/*.h>,
We can follow the style.
> +#include <linux/jump_label.h>
> +#include <linux/kasan-checks.h>
> +#include <linux/kernel.h>
> +
> +#include <net/checksum.h>
> +
> +/* Default version is sufficient for 32 bit */
> +#ifndef CONFIG_32BIT
> +__sum16 csum_ipv6_magic(const struct in6_addr *saddr,
> + const struct in6_addr *daddr,
> + __u32 len, __u8 proto, __wsum csum)
> +{
> + unsigned int ulen, uproto;
> + unsigned long sum = csum;
> +
> + sum += saddr->s6_addr32[0];
> + sum += saddr->s6_addr32[1];
> + sum += saddr->s6_addr32[2];
> + sum += saddr->s6_addr32[3];
> +
> + sum += daddr->s6_addr32[0];
> + sum += daddr->s6_addr32[1];
> + sum += daddr->s6_addr32[2];
> + sum += daddr->s6_addr32[3];
> +
> + ulen = htonl((unsigned int)len);
> + sum += ulen;
> +
> + uproto = htonl(proto);
> + sum += uproto;
> +
> + /*
> + * Zbb support saves 4 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);
> + asm(".option push \n\
> + .option arch,+zbb \n\
> + rori %[fold_temp], %[sum], 32 \n\
> + add %[sum], %[fold_temp], %[sum]
> \n\
> + srli %[sum], %[sum], 32 \n\
> + not %[fold_temp], %[sum] \n\
> + roriw %[sum], %[sum], 16 \n\
> + subw %[sum], %[fold_temp], %[sum]
> \n\
> + .option pop"
> + : [sum] "+r" (sum), [fold_temp] "=&r" (fold_temp));
> + return (__force __sum16)(sum >> 16);
> + }
> +no_zbb:
> + sum += ror64(sum, 32);
> + sum >>= 32;
> + return csum_fold((__force __wsum)sum);
> +}
> +EXPORT_SYMBOL(csum_ipv6_magic);
> +#endif /* !CONFIG_32BIT */
> +
> +#ifdef CONFIG_32BIT
> +#define OFFSET_MASK 3
> +#elif CONFIG_64BIT
> +#define OFFSET_MASK 7
> +#endif
> +
> +static inline __no_sanitize_address unsigned long
> +do_csum_common(const unsigned long *ptr, const unsigned char *buff, int
> len,
> + unsigned long data)
> +{
> + unsigned int shift;
> + const unsigned long *end;
> + unsigned long csum = 0, carry = 0;
> +
> + end = (const unsigned long *)(buff + len);
> +
> + /*
> + * 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);
"len" is not used in below code, so the above line is unnecessary.
Can we consolidate the two parameters of "buff" and "len" into one parameter "end"?
> + 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;
> +
> + return csum;
> +}
> +
> +/*
> + * 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.
> + */
> +static inline __no_sanitize_address unsigned int
> +do_csum_with_alignment(const unsigned char *buff, int len)
> +{
> + unsigned int offset, shift;
> + unsigned long csum, data;
> + const unsigned long *ptr;
> +
> + /*
> + * 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
> +
> + csum = do_csum_common(ptr, buff, len, data);
> +
> + /*
> + * 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)
> + : [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;
> +}
> +
> +/*
> + * Does not perform alignment, should only be used if machine has fast
> + * misaligned accesses, or when buff is known to be aligned.
> + */
> +static inline unsigned int do_csum_no_alignment(const unsigned char *buff,
> int len)
> +{
> + unsigned long csum, data;
> + const unsigned long *ptr;
> +
kasan_check_read() missing here.
> + ptr = (const unsigned long *)(buff);
> +
> + data = *(ptr++);
> +
> + csum = do_csum_common(ptr, buff, len, data);
> +
> + /*
> + * 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 (".option push \n\
> + .option arch,+zbb \n\
> + rori %[fold_temp], %[csum], 16 \n\
> + add %[csum], %[fold_temp], %[csum] \n\
> + .option pop"
> + : [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp)
> + :
> + : );
> +
> +#else /* !CONFIG_32BIT */
> + 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\
> + roriw %[fold_temp], %[csum], 16 \n\
> + addw %[csum], %[fold_temp], %[csum] \n\
> + .option pop"
> + : [csum] "+r" (csum), [fold_temp] "=&r" (fold_temp)
> + :
> + : );
> +#endif /* !CONFIG_32BIT */
> + return csum >> 16;
> + }
> +no_zbb:
> +#ifndef CONFIG_32BIT
> + csum += ror64(csum, 32);
> + csum >>= 32;
> +#endif
> + csum = (u32)csum + ror32((u32)csum, 16);
> + return csum >> 16;
> +}
The algorithm part looks good to me.
BRs,
Xiao
> +
> +/*
> + * Perform a checksum on an arbitrary memory address.
> + * Will do a light-weight address alignment if buff is misaligned, unless
> + * cpu supports fast misaligned accesses.
> + */
> +unsigned int do_csum(const unsigned char *buff, int len)
> +{
> + if (unlikely(len <= 0))
> + return 0;
> +
> + /*
> + * Significant performance gains can be seen by not doing alignment
> + * on machines with fast misaligned accesses.
> + *
> + * There is some duplicate code between the "with_alignment" and
> + * "no_alignment" implmentations, but the overlap is too awkward to
> be
> + * able to fit in one function without introducing multiple static
> + * branches. The largest chunk of overlap was delegated into the
> + * do_csum_common function.
> + */
> + if (static_branch_likely(&fast_misaligned_access_speed_key))
> + return do_csum_no_alignment(buff, len);
> +
> + if (((unsigned long)buff & OFFSET_MASK) == 0)
> + return do_csum_no_alignment(buff, len);
> +
> + return do_csum_with_alignment(buff, len);
> +}
>
> --
> 2.34.1
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