[RFC patch 3/4] riscv: Introduce alternative mechanism to apply errata solution
Vincent Chen
vincent.chen at sifive.com
Mon Mar 8 03:58:16 GMT 2021
Introduce the "alternative" mechanism from ARM64 and x86 to apply the CPU
vendors' errata solution at runtime. The main purpose of this patch is
to provide a framework. Therefore, the implementation is quite basic for
now so that some scenarios could not use this schemei, such as patching
code to a module, relocating the patching code and heterogeneous CPU
topology.
Users could use the macro ALTERNATIVE to apply an errata to the existing
code flow. In the macro ALTERNATIVE, users need to specify the manufacturer
information(vendorid, archid, and impid) for this errata. Therefore, kernel
will know this errata is suitable for which CPU core. During the booting
procedure, kernel will select the errata required by the CPU core and then
patch it. It means that the kernel only applies the errata to the specified
CPU core. In this case the vendor's errata does not affect each other at
runtime. The above patching procedure only occurs during the booting phase,
so we only take the overhead of the "alternative" mechanism once.
This "alternative" mechanism is enabled by default to ensure that all
required errata will be applied. However, users can disable this feature by
the Kconfig "CONFIG_RISCV_ERRATA_ALTERNATIVE".
Signed-off-by: Vincent Chen <vincent.chen at sifive.com>
---
arch/riscv/Kconfig | 1 +
arch/riscv/Kconfig.erratas | 12 +++
arch/riscv/Makefile | 1 +
arch/riscv/errata/Makefile | 1 +
arch/riscv/errata/alternative.c | 69 +++++++++++++++++
arch/riscv/include/asm/alternative-macros.h | 110 ++++++++++++++++++++++++++++
arch/riscv/include/asm/alternative.h | 44 +++++++++++
arch/riscv/include/asm/asm.h | 1 +
arch/riscv/include/asm/errata_list.h | 8 ++
arch/riscv/include/asm/sections.h | 2 +
arch/riscv/include/asm/vendorid_list.h | 6 ++
arch/riscv/kernel/smpboot.c | 4 +
arch/riscv/kernel/vmlinux.lds.S | 14 ++++
13 files changed, 273 insertions(+)
create mode 100644 arch/riscv/Kconfig.erratas
create mode 100644 arch/riscv/errata/Makefile
create mode 100644 arch/riscv/errata/alternative.c
create mode 100644 arch/riscv/include/asm/alternative-macros.h
create mode 100644 arch/riscv/include/asm/alternative.h
create mode 100644 arch/riscv/include/asm/errata_list.h
create mode 100644 arch/riscv/include/asm/vendorid_list.h
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index a998babc1237..2e26251fe1f2 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -204,6 +204,7 @@ config LOCKDEP_SUPPORT
def_bool y
source "arch/riscv/Kconfig.socs"
+source "arch/riscv/Kconfig.erratas"
menu "Platform type"
diff --git a/arch/riscv/Kconfig.erratas b/arch/riscv/Kconfig.erratas
new file mode 100644
index 000000000000..4d0bafc536df
--- /dev/null
+++ b/arch/riscv/Kconfig.erratas
@@ -0,0 +1,12 @@
+menu "CPU errata selection"
+
+config RISCV_ERRATA_ALTERNATIVE
+ bool "RISC-V alternative scheme"
+ default y
+ help
+ This Kconfig allows the kernel to automatically patch the
+ errata required by the execution platform at run time. The
+ code patching is performed once in the boot stages. It means
+ that the overhead from this mechanism is just taken once.
+
+endmenu
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 1368d943f1f3..1f5c03082976 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -87,6 +87,7 @@ KBUILD_IMAGE := $(boot)/Image.gz
head-y := arch/riscv/kernel/head.o
core-y += arch/riscv/
+core-$(CONFIG_RISCV_ERRATA_ALTERNATIVE) += arch/riscv/errata/
libs-y += arch/riscv/lib/
libs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
diff --git a/arch/riscv/errata/Makefile b/arch/riscv/errata/Makefile
new file mode 100644
index 000000000000..43e6d5424367
--- /dev/null
+++ b/arch/riscv/errata/Makefile
@@ -0,0 +1 @@
+obj-y += alternative.o
diff --git a/arch/riscv/errata/alternative.c b/arch/riscv/errata/alternative.c
new file mode 100644
index 000000000000..052affdce6eb
--- /dev/null
+++ b/arch/riscv/errata/alternative.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * alternative runtime patching
+ * inspired by the ARM64 and x86 version
+ *
+ * Copyright (C) 2021 Sifive.
+ */
+
+#include <linux/init.h>
+#include <linux/cpu.h>
+#include <linux/uaccess.h>
+#include <asm/patch.h>
+#include <asm/alternative.h>
+#include <asm/sections.h>
+
+struct alt_region {
+ struct alt_entry *begin;
+ struct alt_entry *end;
+};
+
+static bool (*errata_checkfunc)(struct alt_entry *alt);
+typedef int (*patch_func_t)(void *addr, const void *insn, size_t size);
+
+static void __apply_alternatives(void *alt_region, void *alt_patch_func)
+{
+ struct alt_entry *alt;
+ struct alt_region *region = alt_region;
+
+ for (alt = region->begin; alt < region->end; alt++) {
+ if (!errata_checkfunc(alt))
+ continue;
+ ((patch_func_t)alt_patch_func)(alt->old_ptr, alt->alt_ptr, alt->alt_len);
+ }
+}
+
+static void __init init_alternative(void)
+{
+ struct errata_checkfunc_id *ptr;
+
+ for (ptr = (struct errata_checkfunc_id *)__alt_checkfunc_table;
+ ptr < (struct errata_checkfunc_id *)__alt_checkfunc_table_end;
+ ptr++) {
+ if (cpu_mfr_info.vendor_id == ptr->vendor_id)
+ errata_checkfunc = ptr->func;
+ }
+}
+
+/*
+ * This is called very early in the boot process (directly after we run
+ * a feature detect on the boot CPU). No need to worry about other CPUs
+ * here.
+ */
+void __init apply_boot_alternatives(void)
+{
+ struct alt_region region;
+
+ /* If called on non-boot cpu things could go wrong */
+ WARN_ON(smp_processor_id() != 0);
+
+ init_alternative();
+
+ if (!errata_checkfunc)
+ return;
+
+ region.begin = (struct alt_entry *)__alt_start;
+ region.end = (struct alt_entry *)__alt_end;
+ __apply_alternatives(®ion, patch_text_nosync);
+}
+
diff --git a/arch/riscv/include/asm/alternative-macros.h b/arch/riscv/include/asm/alternative-macros.h
new file mode 100644
index 000000000000..7b6f0c94b1fb
--- /dev/null
+++ b/arch/riscv/include/asm/alternative-macros.h
@@ -0,0 +1,110 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_ALTERNATIVE_MACROS_H
+#define __ASM_ALTERNATIVE_MACROS_H
+
+#ifdef CONFIG_RISCV_ERRATA_ALTERNATIVE
+
+#ifndef __ASSEMBLY__
+
+#include <asm/asm.h>
+#include <linux/stringify.h>
+
+#define ALT_ENTRY(oldptr, altptr, vendor_id, errata_id, altlen) \
+ RISCV_PTR " " oldptr "\n" \
+ RISCV_PTR " " altptr "\n" \
+ REG_ASM " " vendor_id "\n" \
+ REG_ASM " " altlen "\n" \
+ ".word " errata_id "\n"
+
+#define __ALTERNATIVE_CFG(oldinsn, altinsn, vendor_id, errata_id, enable) \
+ "886 :\n" \
+ oldinsn "\n" \
+ ".if " __stringify(enable) " == 1\n" \
+ "887 :\n" \
+ ".pushsection .alternative, \"a\"\n" \
+ ALT_ENTRY("886b", "888f", __stringify(vendor_id), __stringify(errata_id), "889f - 888f") \
+ ".popsection\n" \
+ ".subsection 1\n" \
+ "888 :\n" \
+ altinsn "\n" \
+ "889 :\n" \
+ ".previous\n" \
+ ".org . - (887b - 886b) + (889b - 888b)\n" \
+ ".org . - (889b - 888b) + (887b - 886b)\n" \
+ ".endif\n"
+
+#define _ALTERNATIVE_CFG(oldinsn, altinsn, vendor_id, errata_id, CONFIG_k) \
+ __ALTERNATIVE_CFG(oldinsn, altinsn, vendor_id, errata_id, IS_ENABLED(CONFIG_k))
+
+#else /* __ASSEMBLY__ */
+
+.macro ALT_ENTRY oldptr altptr vendor_id errata_id alt_len
+ RISCV_PTR \oldptr
+ RISCV_PTR \altptr
+ REG_ASM \vendor_id
+ REG_ASM \alt_len
+ .word \errata_id
+.endm
+
+.macro __ALTERNATIVE_CFG insn1 insn2 vendor_id errata_id enable = 1
+886 :
+ \insn1
+ .if \enable
+887 :
+ .pushsection .alternative, "a"
+ ALT_ENTRY 886b, 888f, \vendor_id, \errata_id, 889f - 888f
+ .popsection
+ .subsection 1
+888 :
+ \insn2
+889 :
+ .previous
+ .org . - (889b - 888b) + (887b - 886b)
+ .org . - (887b - 886b) + (889b - 888b)
+ .endif
+.endm
+
+#define _ALTERNATIVE_CFG(oldinsn, altinsn, vendor_id, errata_id, CONFIG_k) \
+ __ALTERNATIVE_CFG oldinsn, altinsn, vendor_id, errata_id, IS_ENABLED(CONFIG_k)
+
+#endif /* !__ASSEMBLY__ */
+
+#else /* !CONFIG_RISCV_ERRATA_ALTERNATIVE*/
+#ifndef __ASSEMBLY__
+
+#define __ALTERNATIVE_CFG(oldinsn) \
+ oldinsn "\n"
+
+#define _ALTERNATIVE_CFG(oldinsn, altinsn, vendor_id, errata_id, CONFIG_k) \
+ __ALTERNATIVE_CFG(oldinsn)
+
+#else /* __ASSEMBLY__ */
+
+.macro __ALTERNATIVE_CFG insn1
+ \insn1
+.endm
+
+#define _ALTERNATIVE_CFG(oldinsn, altinsn, vendor_id, errata_id, CONFIG_k) \
+ __ALTERNATIVE_CFG oldinsn
+
+#endif /* !__ASSEMBLY__ */
+#endif /* CONFIG_RISCV_ERRATA_ALTERNATIVE */
+
+/*
+ * Usage:
+ * ALTERNATIVE(oldinsn, altinsn, vendor_id, errata_id, CONFIG_k)
+ * in the assembly code. Otherwise,
+ * asm(ALTERNATIVE(oldinsn, altinsn, vendor_id, errata_id, CONFIG_k));
+ *
+ * oldinsn: The old instruction which will be replaced.
+ * altinsn: The replacement instruction.
+ * vendor_id: The CPU vendor ID.
+ * errata_id: The errata ID.
+ * CONFIG_k: The Kconfig of this errata. The instructions replacement can
+ * be disabled by this Kconfig. When Kconfig is disabled, the
+ * oldinsn will always be executed.
+ */
+#define ALTERNATIVE(oldinsn, altinsn, vendor_id, errata_id, CONFIG_k) \
+ _ALTERNATIVE_CFG(oldinsn, altinsn, vendor_id, errata_id, CONFIG_k)
+
+#endif
diff --git a/arch/riscv/include/asm/alternative.h b/arch/riscv/include/asm/alternative.h
new file mode 100644
index 000000000000..98a0ea331a27
--- /dev/null
+++ b/arch/riscv/include/asm/alternative.h
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2021 Sifive.
+ */
+
+#ifndef __ASM_ALTERNATIVE_H
+#define __ASM_ALTERNATIVE_H
+
+#define ERRATA_STRING_LENGTH_MAX 32
+
+#include <asm/alternative-macros.h>
+
+#ifndef __ASSEMBLY__
+
+#include <linux/init.h>
+#include <linux/types.h>
+#include <linux/stddef.h>
+#include <asm/hwcap.h>
+
+void __init apply_boot_alternatives(void);
+
+struct alt_entry {
+ void *old_ptr; /* address of original instruciton or data */
+ void *alt_ptr; /* address of replacement instruction or data */
+ unsigned long vendor_id; /* cpu vendor id */
+ unsigned long alt_len; /* The replacement size */
+ unsigned int errata_id; /* The errata id */
+} __packed;
+
+struct errata_checkfunc_id {
+ unsigned long vendor_id;
+ bool (*func)(struct alt_entry *alt);
+};
+
+extern struct cpu_manufacturer_info_t cpu_mfr_info;
+
+#define REGISTER_ERRATA_CHECKFUNC(checkfunc, vendorid) \
+ static const struct errata_checkfunc_id _errata_check_##vendorid \
+ __used __section(".alt_checkfunc_table") \
+ __aligned(__alignof__(struct errata_checkfunc_id)) = \
+ { .vendor_id = vendorid, \
+ .func = checkfunc }
+#endif
+#endif
diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h
index 9c992a88d858..e20646aa97e5 100644
--- a/arch/riscv/include/asm/asm.h
+++ b/arch/riscv/include/asm/asm.h
@@ -23,6 +23,7 @@
#define REG_L __REG_SEL(ld, lw)
#define REG_S __REG_SEL(sd, sw)
#define REG_SC __REG_SEL(sc.d, sc.w)
+#define REG_ASM __REG_SEL(.dword, .word)
#define SZREG __REG_SEL(8, 4)
#define LGREG __REG_SEL(3, 2)
diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
new file mode 100644
index 000000000000..5e5a1fcd90ba
--- /dev/null
+++ b/arch/riscv/include/asm/errata_list.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2021 Sifive.
+ */
+
+#ifdef CONFIG_SOC_SIFIVE
+#define ERRATA_NUMBER 0
+#endif
diff --git a/arch/riscv/include/asm/sections.h b/arch/riscv/include/asm/sections.h
index 1595c5b60cfd..d13160f46d4e 100644
--- a/arch/riscv/include/asm/sections.h
+++ b/arch/riscv/include/asm/sections.h
@@ -11,5 +11,7 @@ extern char _start[];
extern char _start_kernel[];
extern char __init_data_begin[], __init_data_end[];
extern char __init_text_begin[], __init_text_end[];
+extern char __alt_checkfunc_table[], __alt_checkfunc_table_end[];
+extern char __alt_start[], __alt_end[];
#endif /* __ASM_SECTIONS_H */
diff --git a/arch/riscv/include/asm/vendorid_list.h b/arch/riscv/include/asm/vendorid_list.h
new file mode 100644
index 000000000000..1f3be47decb6
--- /dev/null
+++ b/arch/riscv/include/asm/vendorid_list.h
@@ -0,0 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2021 SiFive
+ */
+
+#define SIFIVE_VENDOR_ID 0x489
diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index 5e276c25646f..9a408e2942ac 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -32,6 +32,7 @@
#include <asm/sections.h>
#include <asm/sbi.h>
#include <asm/smp.h>
+#include <asm/alternative.h>
#include "head.h"
@@ -40,6 +41,9 @@ static DECLARE_COMPLETION(cpu_running);
void __init smp_prepare_boot_cpu(void)
{
init_cpu_topology();
+#ifdef CONFIG_RISCV_ERRATA_ALTERNATIVE
+ apply_boot_alternatives();
+#endif
}
void __init smp_prepare_cpus(unsigned int max_cpus)
diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index de03cb22d0e9..6503dfca65b0 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -90,6 +90,20 @@ SECTIONS
}
__init_data_end = .;
+
+ . = ALIGN(8);
+ .alt_checkfunc_table : {
+ __alt_checkfunc_table = .;
+ *(.alt_checkfunc_table)
+ __alt_checkfunc_table_end = .;
+ }
+
+ . = ALIGN(8);
+ .alternative : {
+ __alt_start = .;
+ *(.alternative)
+ __alt_end = .;
+ }
__init_end = .;
/* Start of data section */
--
2.7.4
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