linux-kernel - [PATCH v6 6/8] x86/segments/64: Rename PER_CPU segment to CPU

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Message-Id: <1537312139-5580-7-git-send-email-chang.seok.bae@intel.com>
Date:   Tue, 18 Sep 2018 16:08:57 -0700
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Markus T Metzger <markus.t.metzger@...el.com>,
        Ravi Shankar <ravi.v.shankar@...el.com>,
        "Chang S . Bae" <chang.seok.bae@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v6 6/8] x86/segments/64: Rename PER_CPU segment to CPU_NUMBER

64-bit doesn't use the entry for per CPU data, but for CPU
(and node) numbers. The change will clarify the real usage
of this entry in GDT.

Suggested-by: H. Peter Anvin <hpa@...or.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Acked-by: Andy Lutomirski <luto@...nel.org>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
---
 arch/x86/entry/vdso/vma.c      | 2 +-
 arch/x86/include/asm/segment.h | 5 ++---
 arch/x86/include/asm/vgtod.h   | 8 ++++----
 3 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 5b8b556..0b114aa 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -359,7 +359,7 @@ static void vgetcpu_cpu_init(void *arg)
 	d.p = 1;		/* Present */
 	d.d = 1;		/* 32-bit */
 
-	write_gdt_entry(get_cpu_gdt_rw(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
+	write_gdt_entry(get_cpu_gdt_rw(cpu), GDT_ENTRY_CPU_NUMBER, &d, DESCTYPE_S);
 }
 
 static int vgetcpu_online(unsigned int cpu)
diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h
index 0ffbe95..3cb2aa5 100644
--- a/arch/x86/include/asm/segment.h
+++ b/arch/x86/include/asm/segment.h
@@ -186,8 +186,7 @@
 #define GDT_ENTRY_TLS_MIN		12
 #define GDT_ENTRY_TLS_MAX		14
 
-/* Abused to load per CPU data from limit */
-#define GDT_ENTRY_PER_CPU		15
+#define GDT_ENTRY_CPU_NUMBER		15
 
 /*
  * Number of entries in the GDT table:
@@ -207,7 +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 __PER_CPU_SEG			(GDT_ENTRY_PER_CPU*8 + 3)
+#define __CPU_NUMBER_SEG		(GDT_ENTRY_CPU_NUMBER*8 + 3)
 
 #endif
 
diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h
index 5374854..4e81ea9 100644
--- a/arch/x86/include/asm/vgtod.h
+++ b/arch/x86/include/asm/vgtod.h
@@ -86,9 +86,9 @@ static inline unsigned int __getcpu(void)
 	unsigned int p;
 
 	/*
-	 * Load per CPU data from GDT.  LSL is faster than RDTSCP and
-	 * works on all CPUs.  This is volatile so that it orders
-	 * correctly wrt barrier() and to keep gcc from cleverly
+	 * Load CPU (and node) number from 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.
 	 *
 	 * If RDPID is available, use it.
@@ -96,7 +96,7 @@ static inline unsigned int __getcpu(void)
 	alternative_io ("lsl %[seg],%[p]",
 			".byte 0xf3,0x0f,0xc7,0xf8", /* RDPID %eax/rax */
 			X86_FEATURE_RDPID,
-			[p] "=a" (p), [seg] "r" (__PER_CPU_SEG));
+			[p] "=a" (p), [seg] "r" (__CPU_NUMBER_SEG));
 
 	return p;
 }
-- 
2.7.4