The following commit has been merged into the x86/percpu branch of tip:
Commit-ID: 59bec00ace28d565ae0a68b23063ef3b961d82d5
Gitweb: https://git.kernel.org/tip/59bec00ace28d565ae0a68b23063ef3b961d82d5
Author: Uros Bizjak <ubizjak@xxxxxxxxx>
AuthorDate: Tue, 17 Oct 2023 18:27:34 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Fri, 20 Oct 2023 12:19:51 +02:00
x86/percpu: Introduce %rip-relative addressing to PER_CPU_VAR()
Introduce x86_64 %rip-relative addressing to the PER_CPU_VAR() macro.
Instructions using %rip-relative address operand are one byte shorter
than their absolute address counterparts and are also compatible with
position independent executable (-fpie) builds. The patch reduces
code size of a test kernel build by 150 bytes.
The PER_CPU_VAR() macro is intended to be applied to a symbol and should
not be used with register operands. Introduce the new __percpu macro and
use it in cmpxchg{8,16}b_emu.S instead.
Also add a missing function comment to this_cpu_cmpxchg8b_emu().
No functional changes intended.
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/include/asm/percpu.h | 12 ++++++++----
arch/x86/lib/cmpxchg16b_emu.S | 12 ++++++------
arch/x86/lib/cmpxchg8b_emu.S | 30 +++++++++++++++++++++---------
3 files changed, 35 insertions(+), 19 deletions(-)
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index ac3220a..bbcc1ca 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -4,17 +4,21 @@
#ifdef CONFIG_X86_64
#define __percpu_seg gs
+#define __percpu_rel (%rip)
#else
#define __percpu_seg fs
+#define __percpu_rel
#endif
#ifdef __ASSEMBLY__
#ifdef CONFIG_SMP
-#define PER_CPU_VAR(var) %__percpu_seg:var
-#else /* ! SMP */
-#define PER_CPU_VAR(var) var
-#endif /* SMP */
+#define __percpu %__percpu_seg:
+#else
+#define __percpu
+#endif
+
+#define PER_CPU_VAR(var) __percpu(var)__percpu_rel
#ifdef CONFIG_X86_64_SMP
#define INIT_PER_CPU_VAR(var) init_per_cpu__##var
diff --git a/arch/x86/lib/cmpxchg16b_emu.S b/arch/x86/lib/cmpxchg16b_emu.S
index 6962df3..4fb4489 100644
--- a/arch/x86/lib/cmpxchg16b_emu.S
+++ b/arch/x86/lib/cmpxchg16b_emu.S
@@ -23,14 +23,14 @@ SYM_FUNC_START(this_cpu_cmpxchg16b_emu)
cli
/* if (*ptr == old) */
- cmpq PER_CPU_VAR(0(%rsi)), %rax
+ cmpq __percpu (%rsi), %rax
jne .Lnot_same
- cmpq PER_CPU_VAR(8(%rsi)), %rdx
+ cmpq __percpu 8(%rsi), %rdx
jne .Lnot_same
/* *ptr = new */
- movq %rbx, PER_CPU_VAR(0(%rsi))
- movq %rcx, PER_CPU_VAR(8(%rsi))
+ movq %rbx, __percpu (%rsi)
+ movq %rcx, __percpu 8(%rsi)
/* set ZF in EFLAGS to indicate success */
orl $X86_EFLAGS_ZF, (%rsp)
@@ -42,8 +42,8 @@ SYM_FUNC_START(this_cpu_cmpxchg16b_emu)
/* *ptr != old */
/* old = *ptr */
- movq PER_CPU_VAR(0(%rsi)), %rax
- movq PER_CPU_VAR(8(%rsi)), %rdx
+ movq __percpu (%rsi), %rax
+ movq __percpu 8(%rsi), %rdx
/* clear ZF in EFLAGS to indicate failure */
andl $(~X86_EFLAGS_ZF), (%rsp)
diff --git a/arch/x86/lib/cmpxchg8b_emu.S b/arch/x86/lib/cmpxchg8b_emu.S
index 4980525..8632d7d 100644
--- a/arch/x86/lib/cmpxchg8b_emu.S
+++ b/arch/x86/lib/cmpxchg8b_emu.S
@@ -24,12 +24,12 @@ SYM_FUNC_START(cmpxchg8b_emu)
pushfl
cli
- cmpl 0(%esi), %eax
+ cmpl (%esi), %eax
jne .Lnot_same
cmpl 4(%esi), %edx
jne .Lnot_same
- movl %ebx, 0(%esi)
+ movl %ebx, (%esi)
movl %ecx, 4(%esi)
orl $X86_EFLAGS_ZF, (%esp)
@@ -38,7 +38,7 @@ SYM_FUNC_START(cmpxchg8b_emu)
RET
.Lnot_same:
- movl 0(%esi), %eax
+ movl (%esi), %eax
movl 4(%esi), %edx
andl $(~X86_EFLAGS_ZF), (%esp)
@@ -53,18 +53,30 @@ EXPORT_SYMBOL(cmpxchg8b_emu)
#ifndef CONFIG_UML
+/*
+ * Emulate 'cmpxchg8b %fs:(%rsi)'
+ *
+ * Inputs:
+ * %esi : memory location to compare
+ * %eax : low 32 bits of old value
+ * %edx : high 32 bits of old value
+ * %ebx : low 32 bits of new value
+ * %ecx : high 32 bits of new value
+ *
+ * Notably this is not LOCK prefixed and is not safe against NMIs
+ */
SYM_FUNC_START(this_cpu_cmpxchg8b_emu)
pushfl
cli
- cmpl PER_CPU_VAR(0(%esi)), %eax
+ cmpl __percpu (%esi), %eax
jne .Lnot_same2
- cmpl PER_CPU_VAR(4(%esi)), %edx
+ cmpl __percpu 4(%esi), %edx
jne .Lnot_same2
- movl %ebx, PER_CPU_VAR(0(%esi))
- movl %ecx, PER_CPU_VAR(4(%esi))
+ movl %ebx, __percpu (%esi)
+ movl %ecx, __percpu 4(%esi)
orl $X86_EFLAGS_ZF, (%esp)
@@ -72,8 +84,8 @@ SYM_FUNC_START(this_cpu_cmpxchg8b_emu)
RET
.Lnot_same2:
- movl PER_CPU_VAR(0(%esi)), %eax
- movl PER_CPU_VAR(4(%esi)), %edx
+ movl __percpu (%esi), %eax
+ movl __percpu 4(%esi), %edx
andl $(~X86_EFLAGS_ZF), (%esp)
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