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Date:   Mon, 25 Sep 2023 11:55:50 -0700
From:   "H. Peter Anvin" <hpa@zytor.com>
To:     "Li, Xin3" <xin3.li@intel.com>,
        "linux-doc@vger.kernel.org" <linux-doc@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 25, 2023 10:56:44 AM PDT, "Li, Xin3" <xin3=2Eli@intel=2Ecom> w=
rote:
>> >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);
>> > }
>> >
>> >-/* 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
>>=20
>> Am I missing something, or is this patch a noop?
>
>Yes, this is a noop, just a cleanup patch w/o functionality change=2E
>
>

It just seems to be completely redundant=2E We can just drop it, no? If we=
 aren't going to explicitly clobber the registers there is no harm in setti=
ng them up for IDT unconditionally=2E