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Subject[PATCH 1/3] x86: Provide a full setup for getcpu on x86-32.
Date
setup_getcpu() configures two things:
- writes the current CPU & node information into the MSR_TSC_AUX.
- writes the same information as a GDT entry.

By using the "full" setup_getcpu() on i386 it is possible to read the
CPU information in userland via rdtscp.

Provide an GDT_ENTRY_CPUNODE for x86-32.
Move the CONFIG_X86_64 so the x86-64 implementation becomes also
available for x86-32.

Reviewed-By: Roland Mainz <roland.mainz@nrubsig.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
arch/x86/include/asm/segment.h | 8 ++++----
arch/x86/kernel/cpu/common.c | 4 +---
2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h
index 2e7890dd58a47..662281c2a907c 100644
--- a/arch/x86/include/asm/segment.h
+++ b/arch/x86/include/asm/segment.h
@@ -96,7 +96,7 @@
*
* 26 - ESPFIX small SS
* 27 - per-cpu [ offset to per-cpu data area ]
- * 28 - unused
+ * 28 - VDSO getcpu
* 29 - unused
* 30 - unused
* 31 - TSS for double fault handler
@@ -119,6 +119,7 @@

#define GDT_ENTRY_ESPFIX_SS 26
#define GDT_ENTRY_PERCPU 27
+#define GDT_ENTRY_CPUNODE 28

#define GDT_ENTRY_DOUBLEFAULT_TSS 31

@@ -158,6 +159,8 @@
# define __KERNEL_PERCPU 0
#endif

+#define __CPUNODE_SEG (GDT_ENTRY_CPUNODE*8 + 3)
+
#else /* 64-bit: */

#include <asm/cache.h>
@@ -226,8 +229,6 @@
#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 VDSO_CPUNODE_BITS 12
#define VDSO_CPUNODE_MASK 0xfff
@@ -265,7 +266,6 @@ static inline void vdso_read_cpunode(unsigned *cpu, unsigned *node)
}

#endif /* !__ASSEMBLY__ */
-#endif /* CONFIG_X86_64 */

#ifdef __KERNEL__

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 3e508f2390983..520a0a2e765d3 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2128,7 +2128,6 @@ static void wait_for_master_cpu(int cpu)
#endif
}

-#ifdef CONFIG_X86_64
static inline void setup_getcpu(int cpu)
{
unsigned long cpudata = vdso_encode_cpunode(cpu, early_cpu_to_node(cpu));
@@ -2150,6 +2149,7 @@ static inline void setup_getcpu(int cpu)
write_gdt_entry(get_cpu_gdt_rw(cpu), GDT_ENTRY_CPUNODE, &d, DESCTYPE_S);
}

+#ifdef CONFIG_X86_64
static inline void ucode_cpu_init(int cpu)
{
if (cpu)
@@ -2169,8 +2169,6 @@ static inline void tss_setup_ist(struct tss_struct *tss)

#else /* CONFIG_X86_64 */

-static inline void setup_getcpu(int cpu) { }
-
static inline void ucode_cpu_init(int cpu)
{
show_ucode_info_early();
--
2.38.1
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