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Peter Anvin" , Peter Zijlstra Subject: [PATCH -tip v3 3/3] x86/percpu: Introduce %rip-relative addressing to PER_CPU_VAR Date: Tue, 17 Oct 2023 18:27:34 +0200 Message-ID: <20231017162811.200569-3-ubizjak@gmail.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20231017162811.200569-1-ubizjak@gmail.com> References: <20231017162811.200569-1-ubizjak@gmail.com> MIME-Version: 1.0 Introduce x86_64 %rip-relative addressing to 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) build. The patch reduces code size of a test kernel build by 150 bytes. PER_CPU_VAR macro is intended to be applied to a symbol and should not be used with register operands. Introduce 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. Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: Peter Zijlstra Signed-off-by: Uros Bizjak --- v2: Introduce PER_CPU_ARG macro to conditionally enable segment registers in cmpxchg{8,16}b_emu.S for CONFIG_SMP. v3: Introduce __percpu macro instead of PER_CPU_ARG (hpa). --- 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 54746903b8c3..02f1780f02f5 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 6962df315793..4fb44894ad87 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 873e4ef23e49..1c96be769adc 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)