On September 23, 2023 2:42:10 AM PDT, Xin Li <xin3.li@xxxxxxxxx> wrote: >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 Am I missing something, or is this patch a noop?