[PATCH v11 35/37] x86/syscall: Split IDT syscall setup code into idt_syscall_init()

[Xin Li <xin3.li@xxxxxxxxx>]

Because FRED uses the ring 3 FRED entrypoint for SYSCALL and SYSENTER and
ERETU is the only legit instruction to return to ring 3, there is NO need
to setup SYSCALL and SYSENTER MSRs for FRED, except the IA32_STAR MSR.

Split IDT syscall setup code into idt_syscall_init() to make it easy to
skip syscall setup code when FRED is enabled.

Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Shan Kang <shan.kang@xxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
---
 arch/x86/kernel/cpu/common.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 20bbedbf6dcb..2ee4e7b597a3 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2071,10 +2071,8 @@ static void wrmsrl_cstar(unsigned long val)
                wrmsrl(MSR_CSTAR, val);
 }
 
-/* May not be marked __init: used by software suspend */
-void syscall_init(void)
+static inline void idt_syscall_init(void)
 {
-       wrmsr(MSR_STAR, 0, (__USER32_CS << 16) | __KERNEL_CS);
        wrmsrl(MSR_LSTAR, (unsigned long)entry_SYSCALL_64);
 
        if (ia32_enabled()) {
@@ -2108,6 +2106,15 @@ void syscall_init(void)
               X86_EFLAGS_AC|X86_EFLAGS_ID);
 }
 
+/* May not be marked __init: used by software suspend */
+void syscall_init(void)
+{
+       /* The default user and kernel segments */
+       wrmsr(MSR_STAR, 0, (__USER32_CS << 16) | __KERNEL_CS);
+
+       idt_syscall_init();
+}
+
 #else  /* CONFIG_X86_64 */
 
 #ifdef CONFIG_STACKPROTECTOR
-- 
2.34.1