From 9ce086df162a50c4fe179e3c3fdd6ff3ae251d6c Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Fri, 19 Mar 2021 15:45:05 +0800 Subject: [PATCH 2613/2944] x86/segments: Introduce the 'CPUNODE' naming to better document the segment limit CPU/node NR trick to #30648216 commit 22245bdf0ad805d6c29f82b6d5e977ee94bb2166 upstream. We have a special segment descriptor entry in the GDT, whose sole purpose is to encode the CPU and node numbers in its limit (size) field. There are user-space instructions that allow the reading of the limit field, which gives us a really fast way to read the CPU and node IDs from the vDSO for example. But the naming of related functionality does not make this clear, at all: VDSO_CPU_SIZE VDSO_CPU_MASK __CPU_NUMBER_SEG GDT_ENTRY_CPU_NUMBER vdso_encode_cpu_node vdso_read_cpu_node There's a number of problems: - The 'VDSO_CPU_SIZE' doesn't really make it clear that these are number of bits, nor does it make it clear which 'CPU' this refers to, i.e. that this is about a GDT entry whose limit encodes the CPU and node number. - Furthermore, the 'CPU_NUMBER' naming is actively misleading as well, because the segment limit encodes not just the CPU number but the node ID as well ... So use a better nomenclature all around: name everything related to this trick as 'CPUNODE', to make it clear that this is something special, and add _BITS to make it clear that these are number of bits, and propagate this to every affected name: VDSO_CPU_SIZE => VDSO_CPUNODE_BITS VDSO_CPU_MASK => VDSO_CPUNODE_MASK __CPU_NUMBER_SEG => __CPUNODE_SEG GDT_ENTRY_CPU_NUMBER => GDT_ENTRY_CPUNODE vdso_encode_cpu_node => vdso_encode_cpunode vdso_read_cpu_node => vdso_read_cpunode This, beyond being less confusing, also makes it easier to grep for all related functionality: $ git grep -i cpunode arch/x86 Also, while at it, fix "return is not a function" style sloppiness in vdso_encode_cpunode(). Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Chang S. Bae Cc: Dave Hansen Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Markus T Metzger Cc: Peter Zijlstra Cc: Ravi Shankar Cc: Rik van Riel Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Link: http://lkml.kernel.org/r/1537312139-5580-2-git-send-email-chang.seok.bae@intel.com Signed-off-by: Ingo Molnar Signed-off-by: Ethan Zhao Signed-off-by: Zelin Deng Reviewed-by: Artie Ding --- arch/x86/entry/vdso/vgetcpu.c | 2 +- arch/x86/include/asm/segment.h | 22 +++++++++++----------- arch/x86/kernel/cpu/common.c | 4 ++-- 3 files changed, 14 insertions(+), 14 deletions(-) diff --git a/arch/x86/entry/vdso/vgetcpu.c b/arch/x86/entry/vdso/vgetcpu.c index de78fc9..edd214f 100644 --- a/arch/x86/entry/vdso/vgetcpu.c +++ b/arch/x86/entry/vdso/vgetcpu.c @@ -13,7 +13,7 @@ notrace long __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused) { - vdso_read_cpu_node(cpu, node); + vdso_read_cpunode(cpu, node); return 0; } diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h index 4d1f6cc..a314087 100644 --- a/arch/x86/include/asm/segment.h +++ b/arch/x86/include/asm/segment.h @@ -186,7 +186,7 @@ #define GDT_ENTRY_TLS_MIN 12 #define GDT_ENTRY_TLS_MAX 14 -#define GDT_ENTRY_CPU_NUMBER 15 +#define GDT_ENTRY_CPUNODE 15 /* * Number of entries in the GDT table: @@ -206,7 +206,7 @@ #define __USER_DS (GDT_ENTRY_DEFAULT_USER_DS*8 + 3) #define __USER32_DS __USER_DS #define __USER_CS (GDT_ENTRY_DEFAULT_USER_CS*8 + 3) -#define __CPU_NUMBER_SEG (GDT_ENTRY_CPU_NUMBER*8 + 3) +#define __CPUNODE_SEG (GDT_ENTRY_CPUNODE*8 + 3) #endif @@ -227,24 +227,24 @@ #ifdef CONFIG_X86_64 /* Bit size and mask of CPU number stored in the per CPU data (and TSC_AUX) */ -#define VDSO_CPU_SIZE 12 -#define VDSO_CPU_MASK 0xfff +#define VDSO_CPUNODE_BITS 12 +#define VDSO_CPUNODE_MASK 0xfff #ifndef __ASSEMBLY__ /* Helper functions to store/load CPU and node numbers */ -static inline unsigned long vdso_encode_cpu_node(int cpu, unsigned long node) +static inline unsigned long vdso_encode_cpunode(int cpu, unsigned long node) { - return ((node << VDSO_CPU_SIZE) | cpu); + return (node << VDSO_CPUNODE_BITS) | cpu; } -static inline void vdso_read_cpu_node(unsigned *cpu, unsigned *node) +static inline void vdso_read_cpunode(unsigned *cpu, unsigned *node) { unsigned int p; /* - * Load CPU and node number from GDT. LSL is faster than RDTSCP + * Load CPU and node number from the GDT. LSL is faster than RDTSCP * and works on all CPUs. This is volatile so that it orders * correctly with respect to barrier() and to keep GCC from cleverly * hoisting it out of the calling function. @@ -254,12 +254,12 @@ static inline void vdso_read_cpu_node(unsigned *cpu, unsigned *node) alternative_io ("lsl %[seg],%[p]", ".byte 0xf3,0x0f,0xc7,0xf8", /* RDPID %eax/rax */ X86_FEATURE_RDPID, - [p] "=a" (p), [seg] "r" (__CPU_NUMBER_SEG)); + [p] "=a" (p), [seg] "r" (__CPUNODE_SEG)); if (cpu) - *cpu = (p & VDSO_CPU_MASK); + *cpu = (p & VDSO_CPUNODE_MASK); if (node) - *node = (p >> VDSO_CPU_SIZE); + *node = (p >> VDSO_CPUNODE_BITS); } #endif /* !__ASSEMBLY__ */ diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index f7d170d..61e882e 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1754,7 +1754,7 @@ static void wait_for_master_cpu(int cpu) #ifdef CONFIG_X86_64 static void setup_getcpu(int cpu) { - unsigned long cpudata = vdso_encode_cpu_node(cpu, early_cpu_to_node(cpu)); + unsigned long cpudata = vdso_encode_cpunode(cpu, early_cpu_to_node(cpu)); struct desc_struct d = { }; if (static_cpu_has(X86_FEATURE_RDTSCP)) @@ -1770,7 +1770,7 @@ static void setup_getcpu(int cpu) d.p = 1; /* Present */ d.d = 1; /* 32-bit */ - write_gdt_entry(get_cpu_gdt_rw(cpu), GDT_ENTRY_CPU_NUMBER, &d, DESCTYPE_S); + write_gdt_entry(get_cpu_gdt_rw(cpu), GDT_ENTRY_CPUNODE, &d, DESCTYPE_S); } #endif -- 1.8.3.1