linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: tip-bot for Ingo Molnar <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: bp@alien8.de, torvalds@linux-foundation.org,
	dave.hansen@linux.intel.com, linux-kernel@vger.kernel.org,
	dvlasenk@redhat.com, luto@kernel.org, mingo@kernel.org,
	chang.seok.bae@intel.com, ravi.v.shankar@intel.com,
	tglx@linutronix.de, markus.t.metzger@intel.com, riel@surriel.com,
	peterz@infradead.org, hpa@zytor.com, brgerst@gmail.com
Subject: [tip:x86/asm] x86/segments: Introduce the 'CPUNODE' naming to better document the segment limit CPU/node NR trick
Date: Mon, 8 Oct 2018 02:59:20 -0700	[thread overview]
Message-ID: <tip-22245bdf0ad805d6c29f82b6d5e977ee94bb2166@git.kernel.org> (raw)
In-Reply-To: <1537312139-5580-2-git-send-email-chang.seok.bae@intel.com>

Commit-ID:  22245bdf0ad805d6c29f82b6d5e977ee94bb2166
Gitweb:     https://git.kernel.org/tip/22245bdf0ad805d6c29f82b6d5e977ee94bb2166
Author:     Ingo Molnar <mingo@kernel.org>
AuthorDate: Mon, 8 Oct 2018 10:41:59 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 8 Oct 2018 10:45:02 +0200

x86/segments: Introduce the 'CPUNODE' naming to better document the segment limit CPU/node NR trick

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 <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Markus T Metzger <markus.t.metzger@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
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 <mingo@kernel.org>
---
 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 de78fc9cd963..edd214f5264d 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 4d1f6cc62e13..a314087add07 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 a148d18a1ef0..7da587f4af52 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1672,7 +1672,7 @@ 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))
@@ -1688,7 +1688,7 @@ 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
 

  parent reply	other threads:[~2018-10-08 10:00 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-18 23:08 [PATCH v6 0/8] x86: infrastructure to enable FSGSBASE Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 1/8] x86/arch_prctl/64: Make ptrace read FS/GS base accurately Chang S. Bae
2018-10-08  9:54   ` [tip:x86/asm] x86/fsgsbase/64: Fix ptrace() to read the " tip-bot for Andy Lutomirski
2018-10-08  9:59   ` tip-bot for Ingo Molnar [this message]
2018-10-08  9:59   ` [tip:x86/asm] x86/fsgsbase/64: Clean up various details tip-bot for Ingo Molnar
2018-09-18 23:08 ` [PATCH v6 2/8] x86/fsgsbase/64: Introduce FS/GS base helper functions Chang S. Bae
2018-10-08  9:55   ` [tip:x86/asm] " tip-bot for Chang S. Bae
2018-10-24 19:01   ` [regression in -rc1] Re: [PATCH v6 2/8] " Andy Lutomirski
2018-10-24 19:13     ` Bae, Chang Seok
2018-10-24 19:22       ` Andy Lutomirski
2018-10-24 19:29         ` Bae, Chang Seok
2018-10-24 19:43           ` Andy Lutomirski
2018-10-24 22:50             ` Bae, Chang Seok
2018-10-25 22:37     ` Andy Lutomirski
2018-09-18 23:08 ` [PATCH v6 3/8] x86/fsgsbase/64: Make ptrace use correct FS/GS base helpers Chang S. Bae
2018-10-08  9:56   ` [tip:x86/asm] x86/fsgsbase/64: Make ptrace use the new " tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 4/8] x86/fsgsbase/64: Use FS/GS base helpers in core dump Chang S. Bae
2018-10-08  9:56   ` [tip:x86/asm] x86/fsgsbase/64: Convert the ELF core dump code to the new FSGSBASE helpers tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 5/8] x86/fsgsbase/64: Factor out load FS/GS segments from __switch_to() Chang S. Bae
2018-10-08  9:57   ` [tip:x86/asm] x86/fsgsbase/64: Factor out FS/GS segment loading " tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 6/8] x86/segments/64: Rename PER_CPU segment to CPU_NUMBER Chang S. Bae
2018-10-08  9:57   ` [tip:x86/asm] x86/segments/64: Rename the GDT PER_CPU entry " tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 7/8] x86/vdso: Introduce helper functions for CPU and node number Chang S. Bae
2018-10-08  9:58   ` [tip:x86/asm] " tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 8/8] x86/vdso: Move out the CPU initialization Chang S. Bae
2018-10-08  8:36   ` Ingo Molnar
2018-10-08  9:58   ` [tip:x86/asm] x86/vdso: Initialize the CPU/node NR segment descriptor earlier tip-bot for Chang S. Bae

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=tip-22245bdf0ad805d6c29f82b6d5e977ee94bb2166@git.kernel.org \
    --to=tipbot@zytor.com \
    --cc=bp@alien8.de \
    --cc=brgerst@gmail.com \
    --cc=chang.seok.bae@intel.com \
    --cc=dave.hansen@linux.intel.com \
    --cc=dvlasenk@redhat.com \
    --cc=hpa@zytor.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-tip-commits@vger.kernel.org \
    --cc=luto@kernel.org \
    --cc=markus.t.metzger@intel.com \
    --cc=mingo@kernel.org \
    --cc=peterz@infradead.org \
    --cc=ravi.v.shankar@intel.com \
    --cc=riel@surriel.com \
    --cc=tglx@linutronix.de \
    --cc=torvalds@linux-foundation.org \
    --subject='Re: [tip:x86/asm] x86/segments: Introduce the '\''CPUNODE'\'' naming to better document the segment limit CPU/node NR trick' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).