[PATCH v2 3/6] x86-64: Use relative per-cpu offsets
From: Brian Gerst
Date: Tue Nov 30 2021 - 15:59:37 EST
The per-cpu section is currently linked at virtual address 0, because
older compilers hardcoded the stack protector canary value at a fixed
offset from the start of the GS segment. Now that the canary is a
normal per-cpu variable, the special handling of the per-cpu section
can be removed.
Signed-off-by: Brian Gerst <brgerst@xxxxxxxxx>
---
arch/x86/include/asm/percpu.h | 22 ------
arch/x86/kernel/head_64.S | 6 +-
arch/x86/kernel/irq_64.c | 1 -
arch/x86/kernel/setup_percpu.c | 12 +--
arch/x86/kernel/vmlinux.lds.S | 27 -------
arch/x86/tools/relocs.c | 135 +--------------------------------
init/Kconfig | 1 -
7 files changed, 6 insertions(+), 198 deletions(-)
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index a3c33b79fb86..5418f0a4d073 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -16,12 +16,6 @@
#define PER_CPU_VAR(var) var
#endif /* SMP */
-#ifdef CONFIG_X86_64_SMP
-#define INIT_PER_CPU_VAR(var) init_per_cpu__##var
-#else
-#define INIT_PER_CPU_VAR(var) var
-#endif
-
#else /* ...!ASSEMBLY */
#include <linux/kernel.h>
@@ -49,22 +43,6 @@
#define __percpu_arg(x) __percpu_prefix "%" #x
-/*
- * Initialized pointers to per-cpu variables needed for the boot
- * processor need to use these macros to get the proper address
- * offset from __per_cpu_load on SMP.
- *
- * There also must be an entry in vmlinux_64.lds.S
- */
-#define DECLARE_INIT_PER_CPU(var) \
- extern typeof(var) init_per_cpu_var(var)
-
-#ifdef CONFIG_X86_64_SMP
-#define init_per_cpu_var(var) init_per_cpu__##var
-#else
-#define init_per_cpu_var(var) var
-#endif
-
/* For arch-specific code, we can use direct single-insn ops (they
* don't give an lvalue though). */
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 833f747e74ee..1b8c9919afdb 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -335,11 +335,7 @@ SYM_CODE_END(vc_boot_ghcb)
__REFDATA
.balign 8
SYM_DATA(initial_code, .quad x86_64_start_kernel)
-#ifdef CONFIG_SMP
-SYM_DATA(initial_gs, .quad __per_cpu_load)
-#else
SYM_DATA(initial_gs, .quad 0)
-#endif
#ifdef CONFIG_AMD_MEM_ENCRYPT
SYM_DATA(initial_vc_handler, .quad handle_vc_boot_ghcb)
#endif
@@ -572,7 +568,7 @@ SYM_DATA_END(level1_fixmap_pgt)
.align 16
SYM_DATA(early_gdt_descr, .word GDT_ENTRIES*8-1)
-SYM_DATA_LOCAL(early_gdt_descr_base, .quad INIT_PER_CPU_VAR(gdt_page))
+SYM_DATA_LOCAL(early_gdt_descr_base, .quad gdt_page)
.align 16
/* This must match the first entry in level2_kernel_pgt */
diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
index 1c0fb96b9e39..df537518983e 100644
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -26,7 +26,6 @@
#include <asm/apic.h>
DEFINE_PER_CPU_PAGE_ALIGNED(struct irq_stack, irq_stack_backing_store) __visible;
-DECLARE_INIT_PER_CPU(irq_stack_backing_store);
#ifdef CONFIG_VMAP_STACK
/*
diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index 7b65275544b2..a2489b31564e 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -26,18 +26,10 @@
DEFINE_PER_CPU_READ_MOSTLY(int, cpu_number);
EXPORT_PER_CPU_SYMBOL(cpu_number);
-#ifdef CONFIG_X86_64
-#define BOOT_PERCPU_OFFSET ((unsigned long)__per_cpu_load)
-#else
-#define BOOT_PERCPU_OFFSET 0
-#endif
-
-DEFINE_PER_CPU_READ_MOSTLY(unsigned long, this_cpu_off) = BOOT_PERCPU_OFFSET;
+DEFINE_PER_CPU_READ_MOSTLY(unsigned long, this_cpu_off);
EXPORT_PER_CPU_SYMBOL(this_cpu_off);
-unsigned long __per_cpu_offset[NR_CPUS] __ro_after_init = {
- [0 ... NR_CPUS-1] = BOOT_PERCPU_OFFSET,
-};
+unsigned long __per_cpu_offset[NR_CPUS] __ro_after_init;
EXPORT_SYMBOL(__per_cpu_offset);
/*
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 18a01ece43ee..a72288fa4691 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -103,9 +103,6 @@ PHDRS {
text PT_LOAD FLAGS(5); /* R_E */
data PT_LOAD FLAGS(6); /* RW_ */
#ifdef CONFIG_X86_64
-#ifdef CONFIG_SMP
- percpu PT_LOAD FLAGS(6); /* RW_ */
-#endif
init PT_LOAD FLAGS(7); /* RWE */
#endif
note PT_NOTE FLAGS(0); /* ___ */
@@ -215,17 +212,6 @@ SECTIONS
__init_begin = .; /* paired with __init_end */
}
-#if defined(CONFIG_X86_64) && defined(CONFIG_SMP)
- /*
- * percpu offsets are zero-based on SMP. PERCPU_VADDR() changes the
- * output PHDR, so the next output section - .init.text - should
- * start another segment - init.
- */
- PERCPU_VADDR(INTERNODE_CACHE_BYTES, 0, :percpu)
- ASSERT(SIZEOF(.data..percpu) < CONFIG_PHYSICAL_START,
- "per-CPU data too large - increase CONFIG_PHYSICAL_START")
-#endif
-
INIT_TEXT_SECTION(PAGE_SIZE)
#ifdef CONFIG_X86_64
:init
@@ -339,9 +325,7 @@ SECTIONS
EXIT_DATA
}
-#if !defined(CONFIG_X86_64) || !defined(CONFIG_SMP)
PERCPU_SECTION(INTERNODE_CACHE_BYTES)
-#endif
. = ALIGN(PAGE_SIZE);
@@ -474,17 +458,6 @@ SECTIONS
. = ASSERT((_end - LOAD_OFFSET <= KERNEL_IMAGE_SIZE),
"kernel image bigger than KERNEL_IMAGE_SIZE");
-#ifdef CONFIG_X86_64
-/*
- * Per-cpu symbols which need to be offset from __per_cpu_load
- * for the boot processor.
- */
-#define INIT_PER_CPU(x) init_per_cpu__##x = ABSOLUTE(x) + __per_cpu_load
-INIT_PER_CPU(gdt_page);
-INIT_PER_CPU(irq_stack_backing_store);
-
-#endif /* CONFIG_X86_64 */
-
#ifdef CONFIG_KEXEC_CORE
#include <asm/kexec.h>
diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index 9b3d51cb2cd1..b27980291ff8 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -83,8 +83,6 @@ static const char * const sym_regex_kernel[S_NSYMTYPES] = {
"__initramfs_start|"
"(jiffies|jiffies_64)|"
#if ELF_BITS == 64
- "__per_cpu_load|"
- "init_per_cpu__.*|"
"__end_rodata_hpage_align|"
#endif
"__vvar_page|"
@@ -280,33 +278,6 @@ static const char *sym_name(const char *sym_strtab, Elf_Sym *sym)
return name;
}
-static Elf_Sym *sym_lookup(const char *symname)
-{
- int i;
- for (i = 0; i < shnum; i++) {
- struct section *sec = &secs[i];
- long nsyms;
- char *strtab;
- Elf_Sym *symtab;
- Elf_Sym *sym;
-
- if (sec->shdr.sh_type != SHT_SYMTAB)
- continue;
-
- nsyms = sec->shdr.sh_size/sizeof(Elf_Sym);
- symtab = sec->symtab;
- strtab = sec->link->strtab;
-
- for (sym = symtab; --nsyms >= 0; sym++) {
- if (!sym->st_name)
- continue;
- if (strcmp(symname, strtab + sym->st_name) == 0)
- return sym;
- }
- }
- return 0;
-}
-
#if BYTE_ORDER == LITTLE_ENDIAN
#define le16_to_cpu(val) (val)
#define le32_to_cpu(val) (val)
@@ -749,80 +720,8 @@ static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel,
}
}
-/*
- * The .data..percpu section is a special case for x86_64 SMP kernels.
- * It is used to initialize the actual per_cpu areas and to provide
- * definitions for the per_cpu variables that correspond to their offsets
- * within the percpu area. Since the values of all of the symbols need
- * to be offsets from the start of the per_cpu area the virtual address
- * (sh_addr) of .data..percpu is 0 in SMP kernels.
- *
- * This means that:
- *
- * Relocations that reference symbols in the per_cpu area do not
- * need further relocation (since the value is an offset relative
- * to the start of the per_cpu area that does not change).
- *
- * Relocations that apply to the per_cpu area need to have their
- * offset adjusted by by the value of __per_cpu_load to make them
- * point to the correct place in the loaded image (because the
- * virtual address of .data..percpu is 0).
- *
- * For non SMP kernels .data..percpu is linked as part of the normal
- * kernel data and does not require special treatment.
- *
- */
-static int per_cpu_shndx = -1;
-static Elf_Addr per_cpu_load_addr;
-
-static void percpu_init(void)
-{
- int i;
- for (i = 0; i < shnum; i++) {
- ElfW(Sym) *sym;
- if (strcmp(sec_name(i), ".data..percpu"))
- continue;
-
- if (secs[i].shdr.sh_addr != 0) /* non SMP kernel */
- return;
-
- sym = sym_lookup("__per_cpu_load");
- if (!sym)
- die("can't find __per_cpu_load\n");
-
- per_cpu_shndx = i;
- per_cpu_load_addr = sym->st_value;
- return;
- }
-}
-
#if ELF_BITS == 64
-/*
- * Check to see if a symbol lies in the .data..percpu section.
- *
- * The linker incorrectly associates some symbols with the
- * .data..percpu section so we also need to check the symbol
- * name to make sure that we classify the symbol correctly.
- *
- * The GNU linker incorrectly associates:
- * __init_begin
- * __per_cpu_load
- *
- * The "gold" linker incorrectly associates:
- * init_per_cpu__gdt_page
- */
-static int is_percpu_sym(ElfW(Sym) *sym, const char *symname)
-{
- int shndx = sym_index(sym);
-
- return (shndx == per_cpu_shndx) &&
- strcmp(symname, "__init_begin") &&
- strcmp(symname, "__per_cpu_load") &&
- strncmp(symname, "init_per_cpu_", 13);
-}
-
-
static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
const char *symname)
{
@@ -833,47 +732,21 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
if (sym->st_shndx == SHN_UNDEF)
return 0;
- /*
- * Adjust the offset if this reloc applies to the percpu section.
- */
- if (sec->shdr.sh_info == per_cpu_shndx)
- offset += per_cpu_load_addr;
-
switch (r_type) {
case R_X86_64_NONE:
- /* NONE can be ignored. */
- break;
-
case R_X86_64_PC32:
case R_X86_64_PLT32:
- /*
- * PC relative relocations don't need to be adjusted unless
- * referencing a percpu symbol.
- *
- * NB: R_X86_64_PLT32 can be treated as R_X86_64_PC32.
- */
- if (is_percpu_sym(sym, symname))
- add_reloc(&relocs32neg, offset);
- break;
-
case R_X86_64_PC64:
/*
- * Only used by jump labels
+ * NONE can be ignored and PC relative relocations don't need
+ * to be adjusted. Because sym must be defined, R_X86_64_PLT32 can
+ * be treated the same way as R_X86_64_PC32.
*/
- if (is_percpu_sym(sym, symname))
- die("Invalid R_X86_64_PC64 relocation against per-CPU symbol %s\n",
- symname);
break;
case R_X86_64_32:
case R_X86_64_32S:
case R_X86_64_64:
- /*
- * References to the percpu area don't need to be adjusted.
- */
- if (is_percpu_sym(sym, symname))
- break;
-
if (shn_abs) {
/*
* Whitelisted absolute symbols do not require
@@ -1175,8 +1048,6 @@ void process(FILE *fp, int use_real_mode, int as_text,
read_strtabs(fp);
read_symtabs(fp);
read_relocs(fp);
- if (ELF_BITS == 64)
- percpu_init();
if (show_absolute_syms) {
print_absolute_symbols();
return;
diff --git a/init/Kconfig b/init/Kconfig
index 41a728debdbd..943552dc9c19 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1714,7 +1714,6 @@ config KALLSYMS_ALL
config KALLSYMS_ABSOLUTE_PERCPU
bool
depends on KALLSYMS
- default X86_64 && SMP
config KALLSYMS_BASE_RELATIVE
bool
--
2.31.1