From 119e9db233ad0f4cbd4cfb9f9385a7bca378b37d Mon Sep 17 00:00:00 2001 From: Zeng Chi Date: Mon, 21 Sep 2026 18:24:42 +0800 Subject: KVM: Don't pre-reserve xarray entries when storing empty/NULL attributes Skip the xarray reservation loop when clearing all memory attributes, as storing NULL only erases the entry and never needs to allocate, so no reservation (and no cleanup of a failed one) is required in that case. Suggested-by: Sean Christopherson Cc: David Ballesteros Signed-off-by: Zeng Chi Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com [sean: split to separate patch] Signed-off-by: Sean Christopherson --- arch/riscv/lib/strlen.S | 133 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 133 insertions(+) create mode 100644 arch/riscv/lib/strlen.S (limited to 'arch/riscv/lib/strlen.S') diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S new file mode 100644 index 000000000..e7736ccda --- /dev/null +++ b/arch/riscv/lib/strlen.S @@ -0,0 +1,133 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ + +#include +#include +#include +#include + +/* int strlen(const char *s) */ +SYM_FUNC_START(strlen) + + __ALTERNATIVE_CFG("nop", "j strlen_zbb", 0, RISCV_ISA_EXT_ZBB, + IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) + + /* + * Returns + * a0 - string length + * + * Parameters + * a0 - String to measure + * + * Clobbers: + * t0, t1 + */ + addi t1, a0, -1 +1: + addi t1, t1, 1 + lbu t0, 0(t1) + bnez t0, 1b + sub a0, t1, a0 + ret + +/* + * Variant of strlen using the ZBB extension if available + */ +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB) +strlen_zbb: + +#ifdef CONFIG_CPU_BIG_ENDIAN +# define CZ clz +# define SHIFT sll +#else +# define CZ ctz +# define SHIFT srl +#endif + +.option push +.option arch,+zbb + + /* + * Returns + * a0 - string length + * + * Parameters + * a0 - String to measure + * + * Clobbers + * t0, t1, t2, t3 + */ + + /* Number of irrelevant bytes in the first word. */ + andi t2, a0, SZREG-1 + + /* Align pointer. */ + andi t0, a0, -SZREG + + li t3, SZREG + sub t3, t3, t2 + slli t2, t2, 3 + + /* Get the first word. */ + REG_L t1, 0(t0) + + /* + * Shift away the partial data we loaded to remove the irrelevant bytes + * preceding the string with the effect of adding NUL bytes at the + * end of the string's first word. + */ + SHIFT t1, t1, t2 + + /* Convert non-NUL into 0xff and NUL into 0x00. */ + orc.b t1, t1 + + /* Convert non-NUL into 0x00 and NUL into 0xff. */ + not t1, t1 + + /* + * Search for the first set bit (corresponding to a NUL byte in the + * original chunk). + */ + CZ t1, t1 + + /* + * The first chunk is special: compare against the number + * of valid bytes in this chunk. + */ + srli a0, t1, 3 + bgtu t3, a0, 2f + + /* Prepare for the word comparison loop. */ + addi t2, t0, SZREG + li t3, -1 + + /* + * Our critical loop is 4 instructions and processes data in + * 4 byte or 8 byte chunks. + */ + .p2align 3 +1: + REG_L t1, SZREG(t0) + addi t0, t0, SZREG + orc.b t1, t1 + beq t1, t3, 1b + + not t1, t1 + CZ t1, t1 + srli t1, t1, 3 + + /* Get number of processed bytes. */ + sub t2, t0, t2 + + /* Add number of characters in the first word. */ + add a0, a0, t2 + + /* Add number of characters in the last word. */ + add a0, a0, t1 +2: + ret + +.option pop +#endif +SYM_FUNC_END(strlen) +SYM_FUNC_ALIAS(__pi_strlen, strlen) +EXPORT_SYMBOL(strlen) -- cgit v1.3.1