Re: [PATCH 1/2] LoongArch: Add alternative runtime patching mechanism
From: Huacai Chen
Date: Mon Oct 24 2022 - 12:13:16 EST
Hi, Jinyang,
On Mon, Oct 24, 2022 at 8:51 PM Jinyang He <hejinyang@xxxxxxxxxxx> wrote:
>
> Hi, Huacai,
>
>
> On 2022/10/24 下午3:04, Huacai Chen wrote:
> > Introduce the "alternative" mechanism from ARM64 and x86 for LoongArch
> > to apply runtime patching. The main purpose of this patch is to provide
> > a framework. In future we can use this mechanism (i.e., the ALTERNATIVE
> > and ALTERNATIVE_2 macros) to optimize hotspot functions according to cpu
> > features.
> >
> > Signed-off-by: Jun Yi <yijun@xxxxxxxxxxx>
> > Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
> > ---
> > arch/loongarch/include/asm/alternative-asm.h | 82 ++++++
> > arch/loongarch/include/asm/alternative.h | 176 ++++++++++++
> > arch/loongarch/include/asm/bugs.h | 15 ++
> > arch/loongarch/include/asm/inst.h | 10 +
> > arch/loongarch/kernel/Makefile | 2 +-
> > arch/loongarch/kernel/alternative.c | 266 +++++++++++++++++++
> > arch/loongarch/kernel/module.c | 16 ++
> > arch/loongarch/kernel/setup.c | 7 +
> > arch/loongarch/kernel/vmlinux.lds.S | 12 +
> > 9 files changed, 585 insertions(+), 1 deletion(-)
> > create mode 100644 arch/loongarch/include/asm/alternative-asm.h
> > create mode 100644 arch/loongarch/include/asm/alternative.h
> > create mode 100644 arch/loongarch/include/asm/bugs.h
> > create mode 100644 arch/loongarch/kernel/alternative.c
> >
> > diff --git a/arch/loongarch/include/asm/alternative-asm.h b/arch/loongarch/include/asm/alternative-asm.h
> > new file mode 100644
> > index 000000000000..f0f32ace29b1
> > --- /dev/null
> > +++ b/arch/loongarch/include/asm/alternative-asm.h
> > @@ -0,0 +1,82 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef _ASM_ALTERNATIVE_ASM_H
> > +#define _ASM_ALTERNATIVE_ASM_H
> > +
> > +#ifdef __ASSEMBLY__
> > +
> > +#include <asm/asm.h>
> > +
> > +/*
> > + * Issue one struct alt_instr descriptor entry (need to put it into
> > + * the section .altinstructions, see below). This entry contains
> > + * enough information for the alternatives patching code to patch an
> > + * instruction. See apply_alternatives().
> > + */
> > +.macro altinstruction_entry orig alt feature orig_len alt_len
> > + .long \orig - .
> > + .long \alt - .
> > + .2byte \feature
> > + .byte \orig_len
> > + .byte \alt_len
> I tried '.byte 256' and gas warned but still finished compiling.
> " warning: value 0x0000000000000100 truncated to 0x0000000000000000 "
> How about add '.if .error .endif' here to check the length.
I think a warning is just enough.
> > +.endm
> > +
> > +/*
> > + * Define an alternative between two instructions. If @feature is
> > + * present, early code in apply_alternatives() replaces @oldinstr with
> > + * @newinstr. ".fill" directive takes care of proper instruction padding
> > + * in case @newinstr is longer than @oldinstr.
> > + */
> > +.macro ALTERNATIVE oldinstr, newinstr, feature
> > +140 :
> > + \oldinstr
> > +141 :
> > + .fill - (((144f-143f)-(141b-140b)) > 0) * ((144f-143f)-(141b-140b)) / 4, 4, 0x03400000
> > +142 :
> > +
> > + .pushsection .altinstructions, "a"
> > + altinstruction_entry 140b, 143f, \feature, 142b-140b, 144f-143f
> > + .popsection
> > +
> > + .subsection 1
> > +143 :
> > + \newinstr
> > +144 :
> > + .previous
> > +.endm
> > +
> > +#define old_len (141b-140b)
> > +#define new_len1 (144f-143f)
> > +#define new_len2 (145f-144f)
> > +
> > +#define alt_max_short(a, b) ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))
> > +
> > +/*
> > + * Same as ALTERNATIVE macro above but for two alternatives. If CPU
> > + * has @feature1, it replaces @oldinstr with @newinstr1. If CPU has
> > + * @feature2, it replaces @oldinstr with @feature2.
> > + */
> > +.macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
> > +140 :
> > + \oldinstr
> > +141 :
> > + .fill - ((alt_max_short(new_len1, new_len2) - (old_len)) > 0) * \
> > + (alt_max_short(new_len1, new_len2) - (old_len)) / 4, 4, 0x03400000
> > +142 :
> > +
> > + .pushsection .altinstructions, "a"
> > + altinstruction_entry 140b, 143f, \feature1, 142b-140b, 144f-143f, 142b-141b
> > + altinstruction_entry 140b, 144f, \feature2, 142b-140b, 145f-144f, 142b-141b
> > + .popsection
> > +
> > + .subsection 1
> > +143 :
> > + \newinstr1
> > +144 :
> > + \newinstr2
> > +145 :
> > + .previous
> > +.endm
> > +
> > +#endif /* __ASSEMBLY__ */
> > +
> > +#endif /* _ASM_ALTERNATIVE_ASM_H */
> > diff --git a/arch/loongarch/include/asm/alternative.h b/arch/loongarch/include/asm/alternative.h
> > new file mode 100644
> > index 000000000000..b4fe66c7067e
> > --- /dev/null
> > +++ b/arch/loongarch/include/asm/alternative.h
> > @@ -0,0 +1,176 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef _ASM_ALTERNATIVE_H
> > +#define _ASM_ALTERNATIVE_H
> > +
> > +#ifndef __ASSEMBLY__
> > +
> > +#include <linux/types.h>
> > +#include <linux/stddef.h>
> > +#include <linux/stringify.h>
> > +#include <asm/asm.h>
> > +
> > +struct alt_instr {
> > + s32 instr_offset; /* offset to original instruction */
> > + s32 replace_offset; /* offset to replacement instruction */
> > + u16 feature; /* feature bit set for replacement */
> > + u8 instrlen; /* length of original instruction */
> > + u8 replacementlen; /* length of new instruction */
> > +} __packed;
> > +
> > +/*
> > + * Debug flag that can be tested to see whether alternative
> > + * instructions were patched in already:
> > + */
> > +extern int alternatives_patched;
> > +extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
> > +
> > +extern void alternative_instructions(void);
> > +extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
> > +
> > +#define b_replacement(num) "664"#num
> > +#define e_replacement(num) "665"#num
> > +
> > +#define alt_end_marker "663"
> > +#define alt_slen "662b-661b"
> > +#define alt_total_slen alt_end_marker"b-661b"
> > +#define alt_rlen(num) e_replacement(num)"f-"b_replacement(num)"f"
> > +
> > +#define __OLDINSTR(oldinstr, num) \
> > + "661:\n\t" oldinstr "\n662:\n" \
> > + ".fill -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * " \
> > + "((" alt_rlen(num) ")-(" alt_slen ")) / 4, 4, 0x03400000\n"
> > +
> > +#define OLDINSTR(oldinstr, num) \
> > + __OLDINSTR(oldinstr, num) \
> > + alt_end_marker ":\n"
> > +
> > +#define alt_max_short(a, b) "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") < (" b ")))))"
> > +
> > +/*
> > + * Pad the second replacement alternative with additional NOPs if it is
> > + * additionally longer than the first replacement alternative.
> > + */
> > +#define OLDINSTR_2(oldinstr, num1, num2) \
> > + "661:\n\t" oldinstr "\n662:\n" \
> > + ".fill -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * " \
> > + "(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) / 4, " \
> > + "4, 0x03400000\n" \
> > + alt_end_marker ":\n"
> > +
> > +#define ALTINSTR_ENTRY(feature, num) \
> > + " .long 661b - .\n" /* label */ \
> > + " .long " b_replacement(num)"f - .\n" /* new instruction */ \
> > + " .2byte " __stringify(feature) "\n" /* feature bit */ \
> > + " .byte " alt_total_slen "\n" /* source len */ \
> > + " .byte " alt_rlen(num) "\n" /* replacement len */
> > +
> > +#define ALTINSTR_REPLACEMENT(newinstr, feature, num) /* replacement */ \
> > + b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n\t"
> > +
> > +/* alternative assembly primitive: */
> > +#define ALTERNATIVE(oldinstr, newinstr, feature) \
> > + OLDINSTR(oldinstr, 1) \
> > + ".pushsection .altinstructions,\"a\"\n" \
> > + ALTINSTR_ENTRY(feature, 1) \
> > + ".popsection\n" \
> > + ".subsection 1\n" \
> > + ALTINSTR_REPLACEMENT(newinstr, feature, 1) \
> > + ".previous\n"
> > +
> > +#define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
> > + OLDINSTR_2(oldinstr, 1, 2) \
> > + ".pushsection .altinstructions,\"a\"\n" \
> > + ALTINSTR_ENTRY(feature1, 1) \
> > + ALTINSTR_ENTRY(feature2, 2) \
> > + ".popsection\n" \
> > + ".subsection 1\n" \
> > + ALTINSTR_REPLACEMENT(newinstr1, feature1, 1) \
> > + ALTINSTR_REPLACEMENT(newinstr2, feature2, 2) \
> > + ".previous\n"
> > +
> > +/*
> > + * Alternative instructions for different CPU types or capabilities.
> > + *
> > + * This allows to use optimized instructions even on generic binary
> > + * kernels.
> > + *
> > + * length of oldinstr must be longer or equal the length of newinstr
> > + * It can be padded with nops as needed.
> > + *
> > + * For non barrier like inlines please define new variants
> > + * without volatile and memory clobber.
> > + */
> > +#define alternative(oldinstr, newinstr, feature) \
> > + (asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory"))
> > +
> > +#define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
> > + (asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory"))
> > +
> > +/*
> > + * Alternative inline assembly with input.
> > + *
> > + * Pecularities:
> > + * No memory clobber here.
> > + * Argument numbers start with 1.
> > + * Best is to use constraints that are fixed size (like (%1) ... "r")
> > + * If you use variable sized constraints like "m" or "g" in the
> > + * replacement make sure to pad to the worst case length.
> > + * Leaving an unused argument 0 to keep API compatibility.
> > + */
> > +#define alternative_input(oldinstr, newinstr, feature, input...) \
> > + (asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) \
> > + : : "i" (0), ## input))
> > +
> > +/*
> > + * This is similar to alternative_input. But it has two features and
> > + * respective instructions.
> > + *
> > + * If CPU has feature2, newinstr2 is used.
> > + * Otherwise, if CPU has feature1, newinstr1 is used.
> > + * Otherwise, oldinstr is used.
> > + */
> > +#define alternative_input_2(oldinstr, newinstr1, feature1, newinstr2, \
> > + feature2, input...) \
> > + (asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, \
> > + newinstr2, feature2) \
> > + : : "i" (0), ## input))
> > +
> > +/* Like alternative_input, but with a single output argument */
> > +#define alternative_io(oldinstr, newinstr, feature, output, input...) \
> > + (asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) \
> > + : output : "i" (0), ## input))
> > +
> > +/* Like alternative_io, but for replacing a direct call with another one. */
> > +#define alternative_call(oldfunc, newfunc, feature, output, input...) \
> > + (asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
>
> Not 'call' but 'bl'? And IMHO it is better to separate these patches
> to several patches and convenient for code review. Such as this patch,
> the 'ALTERNATIVE_2' and 'C inline assembly' is not used in [patch2/2],
> these features can be added after [patch2/2] or in the future.
OK, unused macros will be removed at this time, and be added in future.
>
>
> > + : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input))
> > +
> > +/*
> > + * Like alternative_call, but there are two features and respective functions.
> > + * If CPU has feature2, function2 is used.
> > + * Otherwise, if CPU has feature1, function1 is used.
> > + * Otherwise, old function is used.
> > + */
> > +#define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2, \
> > + output, input...) \
> > + (asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
> > + "call %P[new2]", feature2) \
> > + : output, ASM_CALL_CONSTRAINT \
> > + : [old] "i" (oldfunc), [new1] "i" (newfunc1), \
> > + [new2] "i" (newfunc2), ## input))
> > +
> > +/*
> > + * use this macro(s) if you need more than one output parameter
> > + * in alternative_io
> > + */
> > +#define ASM_OUTPUT2(a...) a
> > +
> > +/*
> > + * use this macro if you need clobbers but no inputs in
> > + * alternative_{input,io,call}()
> > + */
> > +#define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
> > +
> > +#endif /* __ASSEMBLY__ */
> > +
> > +#endif /* _ASM_ALTERNATIVE_H */
> > diff --git a/arch/loongarch/include/asm/bugs.h b/arch/loongarch/include/asm/bugs.h
> > new file mode 100644
> > index 000000000000..651fffe1f743
> > --- /dev/null
> > +++ b/arch/loongarch/include/asm/bugs.h
> > @@ -0,0 +1,15 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * This is included by init/main.c to check for architecture-dependent bugs.
> > + *
> > + * Copyright (C) 2020-2021 Loongson Technology Corporation Limited
> > + */
> > +#ifndef _ASM_BUGS_H
> > +#define _ASM_BUGS_H
> > +
> > +#include <asm/cpu.h>
> > +#include <asm/cpu-info.h>
> > +
> > +extern void check_bugs(void);
> > +
> > +#endif /* _ASM_BUGS_H */
> > diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
> > index 889d6c9fc2b6..bd4c116aa73d 100644
> > --- a/arch/loongarch/include/asm/inst.h
> > +++ b/arch/loongarch/include/asm/inst.h
> > @@ -8,6 +8,7 @@
> > #include <linux/types.h>
> > #include <asm/asm.h>
> >
> > +#define INSN_NOP 0x03400000
> > #define INSN_BREAK 0x002a0000
> >
> > #define ADDR_IMMMASK_LU52ID 0xFFF0000000000000
> > @@ -28,6 +29,7 @@ enum reg0i26_op {
> > enum reg1i20_op {
> > lu12iw_op = 0x0a,
> > lu32id_op = 0x0b,
> > + pcaddi_op = 0x0c,
> > pcaddu12i_op = 0x0e,
> > pcaddu18i_op = 0x0f,
> > };
> > @@ -35,6 +37,8 @@ enum reg1i20_op {
> > enum reg1i21_op {
> > beqz_op = 0x10,
> > bnez_op = 0x11,
> > + bceqz_op = 0x12,
> > + bcnez_op = 0x12,
> > };
> >
> > enum reg2_op {
> > @@ -315,6 +319,12 @@ static inline bool is_imm_negative(unsigned long val, unsigned int bit)
> > return val & (1UL << (bit - 1));
> > }
> >
> > +static inline bool is_pc_ins(union loongarch_instruction *ip)
> > +{
> > + return ip->reg1i20_format.opcode >= pcaddi_op &&
> > + ip->reg1i20_format.opcode <= pcaddu18i_op;
> > +}
> > +
> > static inline bool is_branch_ins(union loongarch_instruction *ip)
> > {
> > return ip->reg1i21_format.opcode >= beqz_op &&
> > diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> > index 2ad2555b53ea..86744531b100 100644
> > --- a/arch/loongarch/kernel/Makefile
> > +++ b/arch/loongarch/kernel/Makefile
> > @@ -8,7 +8,7 @@ extra-y := vmlinux.lds
> > obj-y += head.o cpu-probe.o cacheinfo.o env.o setup.o entry.o genex.o \
> > traps.o irq.o idle.o process.o dma.o mem.o io.o reset.o switch.o \
> > elf.o syscall.o signal.o time.o topology.o inst.o ptrace.o vdso.o \
> > - unaligned.o
> > + alternative.o unaligned.o
> >
> > obj-$(CONFIG_ACPI) += acpi.o
> > obj-$(CONFIG_EFI) += efi.o
> > diff --git a/arch/loongarch/kernel/alternative.c b/arch/loongarch/kernel/alternative.c
> > new file mode 100644
> > index 000000000000..43434150b853
> > --- /dev/null
> > +++ b/arch/loongarch/kernel/alternative.c
> > @@ -0,0 +1,263 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +#include <linux/mm.h>
> > +#include <linux/module.h>
> > +#include <asm/alternative.h>
> > +#include <asm/cacheflush.h>
> > +#include <asm/inst.h>
> > +#include <asm/sections.h>
> > +
> > +int __read_mostly alternatives_patched;
> > +
> > +EXPORT_SYMBOL_GPL(alternatives_patched);
> > +
> > +#define MAX_PATCH_SIZE (((u8)(-1)) / LOONGARCH_INSN_SIZE)
> > +
> > +static int __initdata_or_module debug_alternative;
> > +
> > +static int __init debug_alt(char *str)
> > +{
> > + debug_alternative = 1;
> > + return 1;
> > +}
> > +__setup("debug-alternative", debug_alt);
> > +
> > +#define DPRINTK(fmt, args...) \
> > +do { \
> > + if (debug_alternative) \
> > + printk(KERN_DEBUG "%s: " fmt "\n", __func__, ##args); \
> > +} while (0)
> > +
> > +#define DUMP_WORDS(buf, count, fmt, args...) \
> > +do { \
> > + if (unlikely(debug_alternative)) { \
> > + int _j; \
> > + union loongarch_instruction *_buf = buf; \
> > + \
> > + if (!(count)) \
> > + break; \
> > + \
> > + printk(KERN_DEBUG fmt, ##args); \
> > + for (_j = 0; _j < count - 1; _j++) \
> > + printk(KERN_CONT "<%08x> ", _buf[_j].word); \
> > + printk(KERN_CONT "<%08x>\n", _buf[_j].word); \
> > + } \
> > +} while (0)
> > +
> > +#define __SIGNEX(X, SIDX) ((X) >= (1 << SIDX) ? ~((1 << SIDX) - 1) | (X) : (X))
> > +#define SIGNEX16(X) __SIGNEX(((unsigned long)(X)), 15)
> > +#define SIGNEX20(X) __SIGNEX(((unsigned long)(X)), 19)
> > +#define SIGNEX21(X) __SIGNEX(((unsigned long)(X)), 20)
> > +#define SIGNEX26(X) __SIGNEX(((unsigned long)(X)), 25)
> > +
> > +static inline unsigned long bs_dest_16(unsigned long now, unsigned int si)
> > +{
> > + return now + (SIGNEX16(si) << 2);
> > +}
> > +
> > +static inline unsigned long bs_dest_21(unsigned long now, unsigned int h, unsigned int l)
> > +{
> > + return now + (SIGNEX21(h << 16 | l) << 2);
> > +}
> > +
> > +static inline unsigned long bs_dest_26(unsigned long now, unsigned int h, unsigned int l)
> > +{
> > + return now + (SIGNEX26(h << 16 | l) << 2);
> > +}
> > +
> > +/* Use this to add nops to a buffer, then text_poke the whole buffer. */
> > +static void __init_or_module add_nops(union loongarch_instruction *insn, int count)
> > +{
> > + while (count--) {
> > + insn->word = INSN_NOP;
> > + insn++;
> > + }
> > +}
> > +
> > +/* Is the jump addr in local .altinstructions */
> > +static inline bool in_alt_jump(unsigned long jump, void *start, void *end)
> > +{
> > + return jump >= (unsigned long)start && jump < (unsigned long)end;
> > +}
> > +
> > +static void __init_or_module recompute_jump(union loongarch_instruction *buf,
> > + union loongarch_instruction *dest, union loongarch_instruction *src,
> > + void *start, void *end)
> > +{
> > + unsigned int si, si_l, si_h;
> > + unsigned long cur_pc, jump_addr, pc;
> > + long offset;
> > +
> > + cur_pc = (unsigned long)src;
> > + pc = (unsigned long)dest;
> > +
> > + si_l = src->reg0i26_format.immediate_l;
> > + si_h = src->reg0i26_format.immediate_h;
> > + switch (src->reg0i26_format.opcode) {
> > + case b_op:
> > + case bl_op:
> > + jump_addr = bs_dest_26(cur_pc, si_h, si_l);
> > + if (in_alt_jump(jump_addr, start, end))
> > + return;
> > + offset = jump_addr - pc;
> > + BUG_ON(offset < -SZ_128M || offset >= SZ_128M);
> > + offset >>= 2;
> > + buf->reg0i26_format.immediate_h = offset >> 16;
> > + buf->reg0i26_format.immediate_l = offset;
> > + return;
> > + }
> > +
> > + si_l = src->reg1i21_format.immediate_l;
> > + si_h = src->reg1i21_format.immediate_h;
> > + switch (src->reg1i21_format.opcode) {
> > + case beqz_op:
> > + case bnez_op:
> > + case bceqz_op:
> > + jump_addr = bs_dest_21(cur_pc, si_h, si_l);
> > + if (in_alt_jump(jump_addr, start, end))
> > + return;
> > + offset = jump_addr - pc;
> > + BUG_ON(offset < -SZ_4M || offset >= SZ_4M);
> > + offset >>= 2;
> > + buf->reg1i21_format.immediate_h = offset >> 16;
> > + buf->reg1i21_format.immediate_l = offset;
> > + return;
> > + }
> > +
> > + si = src->reg2i16_format.immediate;
> > + switch (src->reg2i16_format.opcode) {
> > + case beq_op:
> > + case bne_op:
> > + case blt_op:
> > + case bge_op:
> > + case bltu_op:
> > + case bgeu_op:
> > + jump_addr = bs_dest_16(cur_pc, si);
> > + if (in_alt_jump(jump_addr, start, end))
> > + return;
> > + offset = jump_addr - pc;
> > + BUG_ON(offset < -SZ_128K || offset >= SZ_128K);
> > + offset >>= 2;
> > + buf->reg2i16_format.immediate = offset;
>
> code indent should use tabs where possible
OK, thanks.
>
>
> > + return;
> > + }
> > +}
> > +
> > +static int __init_or_module copy_alt_insns(union loongarch_instruction *buf,
> > + union loongarch_instruction *dest, union loongarch_instruction *src, int nr)
> > +{
> > + int i;
> > +
> > + for (i = 0; i < nr; i++) {
> > + buf[i].word = src[i].word;
> > +
> > + if (is_branch_ins(&src[i]) &&
> > + src[i].reg2i16_format.opcode != jirl_op) {
> > + recompute_jump(&buf[i], &dest[i], &src[i], src, src + nr);
> > + } else if (is_pc_ins(&src[i])) {
> > + pr_err("Not support pcrel instruction at present!");
> > + return -EINVAL;
> > + }
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +/*
> > + * text_poke_early - Update instructions on a live kernel at boot time
> > + *
> > + * When you use this code to patch more than one byte of an instruction
> > + * you need to make sure that other CPUs cannot execute this code in parallel.
> > + * Also no thread must be currently preempted in the middle of these
> > + * instructions. And on the local CPU you need to be protected again NMI or MCE
> > + * handlers seeing an inconsistent instruction while you patch.
> > + */
> > +static void *__init_or_module text_poke_early(union loongarch_instruction *insn,
> > + union loongarch_instruction *buf, unsigned int nr)
> > +{
> > + int i;
> > + unsigned long flags;
> > +
> > + local_irq_save(flags);
> > +
> > + for (i = 0; i < nr; i++)
> > + insn[i].word = buf[i].word;
> > +
> > + local_irq_restore(flags);
> > +
> > + wbflush();
> > + flush_icache_range((unsigned long)insn, (unsigned long)(insn + nr));
>
> nr * LOONGARCH_INSN_SIZE
insn is a pointer, so (insn + nr) is just OK.
Huacai
>
>
> Thanks,
>
> Jinyang
>
>
> > +
> > + return insn;
> > +}
> > +
> > +/*
> > + * Replace instructions with better alternatives for this CPU type. This runs
> > + * before SMP is initialized to avoid SMP problems with self modifying code.
> > + * This implies that asymmetric systems where APs have less capabilities than
> > + * the boot processor are not handled. Tough. Make sure you disable such
> > + * features by hand.
> > + */
> > +void __init_or_module apply_alternatives(struct alt_instr *start, struct alt_instr *end)
> > +{
> > + struct alt_instr *a;
> > + unsigned int nr_instr, nr_repl, nr_insnbuf;
> > + union loongarch_instruction *instr, *replacement;
> > + union loongarch_instruction insnbuf[MAX_PATCH_SIZE];
> > +
> > + DPRINTK("alt table %px, -> %px", start, end);
> > + /*
> > + * The scan order should be from start to end. A later scanned
> > + * alternative code can overwrite previously scanned alternative code.
> > + * Some kernel functions (e.g. memcpy, memset, etc) use this order to
> > + * patch code.
> > + *
> > + * So be careful if you want to change the scan order to any other
> > + * order.
> > + */
> > + for (a = start; a < end; a++) {
> > + nr_insnbuf = 0;
> > +
> > + instr = (void *)&a->instr_offset + a->instr_offset;
> > + replacement = (void *)&a->replace_offset + a->replace_offset;
> > +
> > + BUG_ON(a->instrlen > sizeof(insnbuf));
> > + BUG_ON(a->instrlen & 0x3);
> > + BUG_ON(a->replacementlen & 0x3);
> > +
> > + nr_instr = a->instrlen / LOONGARCH_INSN_SIZE;
> > + nr_repl = a->replacementlen / LOONGARCH_INSN_SIZE;
> > +
> > + if (!cpu_has(a->feature)) {
> > + DPRINTK("feat not exist: %d, old: (%px len: %d), repl: (%px, len: %d)",
> > + a->feature, instr, a->instrlen,
> > + replacement, a->replacementlen);
> > +
> > + continue;
> > + }
> > +
> > + DPRINTK("feat: %d, old: (%px len: %d), repl: (%px, len: %d)",
> > + a->feature, instr, a->instrlen,
> > + replacement, a->replacementlen);
> > +
> > + DUMP_WORDS(instr, nr_instr, "%px: old_insn: ", instr);
> > + DUMP_WORDS(replacement, nr_repl, "%px: rpl_insn: ", replacement);
> > +
> > + copy_alt_insns(insnbuf, instr, replacement, nr_repl);
> > + nr_insnbuf = nr_repl;
> > +
> > + if (nr_instr > nr_repl) {
> > + add_nops(insnbuf + nr_repl, nr_instr - nr_repl);
> > + nr_insnbuf += nr_instr - nr_repl;
> > + }
> > + DUMP_WORDS(insnbuf, nr_insnbuf, "%px: final_insn: ", instr);
> > +
> > + text_poke_early(instr, insnbuf, nr_insnbuf);
> > + }
> > +}
> > +
> > +void __init alternative_instructions(void)
> > +{
> > + apply_alternatives(__alt_instructions, __alt_instructions_end);
> > +
> > + alternatives_patched = 1;
> > +}
> > diff --git a/arch/loongarch/kernel/module.c b/arch/loongarch/kernel/module.c
> > index 097595b2fc14..669e750917a3 100644
> > --- a/arch/loongarch/kernel/module.c
> > +++ b/arch/loongarch/kernel/module.c
> > @@ -17,6 +17,7 @@
> > #include <linux/fs.h>
> > #include <linux/string.h>
> > #include <linux/kernel.h>
> > +#include <asm/alternative.h>
> >
> > static int rela_stack_push(s64 stack_value, s64 *rela_stack, size_t *rela_stack_top)
> > {
> > @@ -456,3 +457,18 @@ void *module_alloc(unsigned long size)
> > return __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END,
> > GFP_KERNEL, PAGE_KERNEL, 0, NUMA_NO_NODE, __builtin_return_address(0));
> > }
> > +
> > +int module_finalize(const Elf_Ehdr *hdr,
> > + const Elf_Shdr *sechdrs,
> > + struct module *mod)
> > +{
> > + const Elf_Shdr *s, *se;
> > + const char *secstrs = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
> > +
> > + for (s = sechdrs, se = sechdrs + hdr->e_shnum; s < se; s++) {
> > + if (!strcmp(".altinstructions", secstrs + s->sh_name))
> > + apply_alternatives((void *)s->sh_addr, (void *)s->sh_addr + s->sh_size);
> > + }
> > +
> > + return 0;
> > +}
> > diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> > index 1eb63fa9bc81..96b6cb5db004 100644
> > --- a/arch/loongarch/kernel/setup.c
> > +++ b/arch/loongarch/kernel/setup.c
> > @@ -31,7 +31,9 @@
> > #include <linux/swiotlb.h>
> >
> > #include <asm/addrspace.h>
> > +#include <asm/alternative.h>
> > #include <asm/bootinfo.h>
> > +#include <asm/bugs.h>
> > #include <asm/cache.h>
> > #include <asm/cpu.h>
> > #include <asm/dma.h>
> > @@ -80,6 +82,11 @@ const char *get_system_type(void)
> > return "generic-loongson-machine";
> > }
> >
> > +void __init check_bugs(void)
> > +{
> > + alternative_instructions();
> > +}
> > +
> > static const char *dmi_string_parse(const struct dmi_header *dm, u8 s)
> > {
> > const u8 *bp = ((u8 *) dm) + dm->length;
> > diff --git a/arch/loongarch/kernel/vmlinux.lds.S b/arch/loongarch/kernel/vmlinux.lds.S
> > index efecda0c2361..733b16e8d55d 100644
> > --- a/arch/loongarch/kernel/vmlinux.lds.S
> > +++ b/arch/loongarch/kernel/vmlinux.lds.S
> > @@ -54,6 +54,18 @@ SECTIONS
> > . = ALIGN(PECOFF_SEGMENT_ALIGN);
> > _etext = .;
> >
> > + /*
> > + * struct alt_inst entries. From the header (alternative.h):
> > + * "Alternative instructions for different CPU types or capabilities"
> > + * Think locking instructions on spinlocks.
> > + */
> > + . = ALIGN(4);
> > + .altinstructions : AT(ADDR(.altinstructions) - LOAD_OFFSET) {
> > + __alt_instructions = .;
> > + *(.altinstructions)
> > + __alt_instructions_end = .;
> > + }
> > +
> > .got : ALIGN(16) { *(.got) }
> > .plt : ALIGN(16) { *(.plt) }
> > .got.plt : ALIGN(16) { *(.got.plt) }
>