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Date:   Mon, 25 Sep 2023 09:07:47 -0700
From:   "H. Peter Anvin" <hpa@zytor.com>
To:     Xin Li <xin3.li@intel.com>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org,
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Subject: =?US-ASCII?Q?Re=3A_=5BPATCH_v11_35/37=5D_x86/syscall=3A_Split_ID?= =?US-ASCII?Q?T_syscall_setup_code_into_idt=5Fsyscall=5Finit=28=29?=
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On September 23, 2023 2:42:10 AM PDT, Xin Li <xin3=2Eli@intel=2Ecom> 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=2E
>
>Split IDT syscall setup code into idt_syscall_init() to make it easy to
>skip syscall setup code when FRED is enabled=2E
>
>Suggested-by: Thomas Gleixner <tglx@linutronix=2Ede>
>Tested-by: Shan Kang <shan=2Ekang@intel=2Ecom>
>Signed-off-by: Xin Li <xin3=2Eli@intel=2Ecom>
>---
> arch/x86/kernel/cpu/common=2Ec | 13 ++++++++++---
> 1 file changed, 10 insertions(+), 3 deletions(-)
>
>diff --git a/arch/x86/kernel/cpu/common=2Ec b/arch/x86/kernel/cpu/common=
=2Ec
>index 20bbedbf6dcb=2E=2E2ee4e7b597a3 100644
>--- a/arch/x86/kernel/cpu/common=2Ec
>+++ b/arch/x86/kernel/cpu/common=2Ec
>@@ -2071,10 +2071,8 @@ static void wrmsrl_cstar(unsigned long val)
> 		wrmsrl(MSR_CSTAR, val);
> }
>=20
>-/* 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);
>=20
> 	if (ia32_enabled()) {
>@@ -2108,6 +2106,15 @@ void syscall_init(void)
> 	       X86_EFLAGS_AC|X86_EFLAGS_ID);
> }
>=20
>+/* 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 */
>=20
> #ifdef CONFIG_STACKPROTECTOR

Am I missing something, or is this patch a noop?