linux-kernel - [PATCH v3 6/7] x86/vdso: Introduce CPU number helper functions

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Date:   Thu,  7 Jun 2018 10:06:07 -0700
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     Andy Lutomirski <luto@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Markus T Metzger <markus.t.metzger@...el.com>,
        "Ravi V . Shankar" <ravi.v.shankar@...el.com>,
        "Chang S . Bae" <chang.seok.bae@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v3 6/7] x86/vdso: Introduce CPU number helper functions

CPU number initialization in vDSO is now a bit cleaned up by
the new helper functions. The helper functions will take
care of combing CPU and node number and reading each from
the combined value.

Suggested-by: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/entry/vdso/vgetcpu.c  |  4 ++--
 arch/x86/entry/vdso/vma.c      | 16 ++++++++--------
 arch/x86/include/asm/segment.h | 28 ++++++++++++++++++++++++++++
 arch/x86/include/asm/vgtod.h   |  2 --
 4 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/arch/x86/entry/vdso/vgetcpu.c b/arch/x86/entry/vdso/vgetcpu.c
index 8ec3d1f..3284069 100644
--- a/arch/x86/entry/vdso/vgetcpu.c
+++ b/arch/x86/entry/vdso/vgetcpu.c
@@ -18,9 +18,9 @@ __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused)
 	p = __getcpu();
 
 	if (cpu)
-		*cpu = p & VGETCPU_CPU_MASK;
+		*cpu = lsl_tscp_to_cpu(p);
 	if (node)
-		*node = p >> 12;
+		*node = lsl_tscp_to_node(p);
 	return 0;
 }
 
diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 833e229..1fc93da 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -340,19 +340,19 @@ static void vgetcpu_cpu_init(void *arg)
 	int cpu = smp_processor_id();
 	struct desc_struct d = { };
 	unsigned long node = 0;
+	unsigned long cpu_number = 0;
 #ifdef CONFIG_NUMA
 	node = cpu_to_node(cpu);
 #endif
+	cpu_number = make_lsl_tscp(cpu, node);
+
 	if (static_cpu_has(X86_FEATURE_RDTSCP))
-		write_rdtscp_aux((node << 12) | cpu);
+		write_rdtscp_aux(cpu_number);
+
+	/* Store cpu number in limit */
+	d.limit0 = cpu_number;
+	d.limit1 = cpu_number >> 16;
 
-	/*
-	 * Store cpu number in limit so that it can be loaded
-	 * quickly in user space in vgetcpu. (12 bits for the CPU
-	 * and 8 bits for the node)
-	 */
-	d.limit0 = cpu | ((node & 0xf) << 12);
-	d.limit1 = node >> 4;
 	d.type = 5;		/* RO data, expand down, accessed */
 	d.dpl = 3;		/* Visible to user code */
 	d.s = 1;		/* Not a system segment */
diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h
index 492e3d1..2169a24 100644
--- a/arch/x86/include/asm/segment.h
+++ b/arch/x86/include/asm/segment.h
@@ -224,6 +224,34 @@
 #define GDT_ENTRY_TLS_ENTRIES		3
 #define TLS_SIZE			(GDT_ENTRY_TLS_ENTRIES* 8)
 
+#ifdef CONFIG_X86_64
+
+/* Bit size and mask of CPU number stored in the per CPU data (and TSC_AUX) */
+#define LSL_TSCP_CPU_SIZE		12
+#define LSL_TSCP_CPU_MASK		0xfff
+
+#ifndef __ASSEMBLY__
+
+/* Helper functions to store/load CPU and node numbers */
+
+static inline unsigned long make_lsl_tscp(int cpu, unsigned long node)
+{
+	return ((node << LSL_TSCP_CPU_SIZE) | cpu);
+}
+
+static inline unsigned int lsl_tscp_to_cpu(unsigned long x)
+{
+	return (x & LSL_TSCP_CPU_MASK);
+}
+
+static inline unsigned int lsl_tscp_to_node(unsigned long x)
+{
+	return (x >> LSL_TSCP_CPU_SIZE);
+}
+
+#endif /* !__ASSEMBLY__ */
+#endif /* CONFIG_X86_64 */
+
 #ifdef __KERNEL__
 
 /*
diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h
index 9cd9036..24e69b3 100644
--- a/arch/x86/include/asm/vgtod.h
+++ b/arch/x86/include/asm/vgtod.h
@@ -79,8 +79,6 @@ static inline void gtod_write_end(struct vsyscall_gtod_data *s)
 
 #ifdef CONFIG_X86_64
 
-#define VGETCPU_CPU_MASK 0xfff
-
 static inline unsigned int __getcpu(void)
 {
 	unsigned int p;
-- 
2.7.4