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Subject[PATCH v2 8/8] x86/vdso: Move out the CPU number store
Date
The CPU (and node) number will be written, as early enough,
to the segment limit of per CPU data and TSC_AUX MSR entry.
The information has been retrieved by vgetcpu in user space
and will be also loaded from the paranoid entry, when
FSGSBASE enabled. So, it is moved out from vDSO to the CPU
initialization path where IST setup is serialized.

Now, redundant setting of the segment in entry/vdso/vma.c
was removed; a substantial code removal. It removes a
hotplug notifier, makes a facility useful to both the kernel
and userspace unconditionally available much sooner, and
unification with i386. (Thanks to HPA for suggesting the
cleanup)

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
---
arch/x86/entry/vdso/vgetcpu.c | 4 ++--
arch/x86/entry/vdso/vma.c | 41 +----------------------------------------
arch/x86/include/asm/segment.h | 25 +++++++++++++++++++++++++
arch/x86/include/asm/vgtod.h | 2 --
arch/x86/kernel/cpu/common.c | 5 +++++
arch/x86/kernel/setup_percpu.c | 25 +++++++++++++++++++++++++
6 files changed, 58 insertions(+), 44 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..3f9d43f 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -332,43 +332,6 @@ static __init int vdso_setup(char *s)
return 0;
}
__setup("vdso=", vdso_setup);
-#endif
-
-#ifdef CONFIG_X86_64
-static void vgetcpu_cpu_init(void *arg)
-{
- int cpu = smp_processor_id();
- struct desc_struct d = { };
- unsigned long node = 0;
-#ifdef CONFIG_NUMA
- node = cpu_to_node(cpu);
-#endif
- if (static_cpu_has(X86_FEATURE_RDTSCP))
- write_rdtscp_aux((node << 12) | cpu);
-
- /*
- * 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 */
- d.p = 1; /* Present */
- d.d = 1; /* 32-bit */
-
- write_gdt_entry(get_cpu_gdt_rw(cpu),
- GDT_ENTRY_CPU_NUMBER,
- &d,
- DESCTYPE_S);
-}
-
-static int vgetcpu_online(unsigned int cpu)
-{
- return smp_call_function_single(cpu, vgetcpu_cpu_init, NULL, 1);
-}

static int __init init_vdso(void)
{
@@ -378,9 +341,7 @@ static int __init init_vdso(void)
init_vdso_image(&vdso_image_x32);
#endif

- /* notifier priority > KVM */
- return cpuhp_setup_state(CPUHP_AP_X86_VDSO_VMA_ONLINE,
- "x86/vdso/vma:online", vgetcpu_online, NULL);
+ return 0;
}
subsys_initcall(init_vdso);
#endif /* CONFIG_X86_64 */
diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h
index fca55d7..a2b1172 100644
--- a/arch/x86/include/asm/segment.h
+++ b/arch/x86/include/asm/segment.h
@@ -236,6 +236,31 @@
#define GDT_ENTRY_TLS_ENTRIES 3
#define TLS_SIZE (GDT_ENTRY_TLS_ENTRIES* 8)

+/* 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
+
#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;
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 38276f5..c7b54f0 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1665,6 +1665,11 @@ void cpu_init(void)

wrmsrl(MSR_FS_BASE, 0);
wrmsrl(MSR_KERNEL_GS_BASE, 0);
+#ifdef CONFIG_NUMA
+ write_rdtscp_aux(make_lsl_tscp(cpu, early_cpu_to_node(cpu)));
+#else
+ write_rdtscp_aux(make_lsl_tscp(cpu, 0));
+#endif
barrier();

x86_configure_nx();
diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index ea554f8..61ab2e2 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -163,6 +163,30 @@ static inline void setup_percpu_segment(int cpu)
#endif
}

+static inline void setup_cpu_number_segment(int cpu)
+{
+#ifdef CONFIG_NUMA
+ unsigned long node = early_cpu_to_node(cpu);
+#else
+ unsigned long node = 0;
+#endif
+ struct desc_struct d = GDT_ENTRY_INIT(0x40f5, 0x0,
+ make_lsl_tscp(cpu, node));
+
+ /*
+ * CPU_NUMBER segment flag
+ * type: R0 data, expand down, accessed
+ * dpl: Visible to user code
+ * s: Not a system segment
+ * p: Present
+ * d: 32-bit
+ */
+ write_gdt_entry(get_cpu_gdt_rw(cpu),
+ GDT_ENTRY_CPU_NUMBER,
+ &d,
+ DESCTYPE_S);
+}
+
void __init setup_per_cpu_areas(void)
{
unsigned int cpu;
@@ -223,6 +247,7 @@ void __init setup_per_cpu_areas(void)
per_cpu(cpu_number, cpu) = cpu;
setup_percpu_segment(cpu);
setup_stack_canary_segment(cpu);
+ setup_cpu_number_segment(cpu);
/*
* Copy data used in early init routines from the
* initial arrays to the per cpu data areas. These
--
2.7.4
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