[PATCH v2 1/3] x86/fred: Parse cmdline param "fred=" in cpu_parse_early_param()

["Xin Li (Intel)" <xin@zytor.com>]

Depending on whether FRED will be used, sysvec_install() installs
a system interrupt handler into FRED system vector dispatch table
or IDT.  However FRED can be disabled later in trap_init(), after
sysvec_install() is called.  E.g., the HYPERVISOR_CALLBACK_VECTOR
handler is registered with sysvec_install() in kvm_guest_init(),
which is called in setup_arch() but way before trap_init().  IOW,
there is a gap between FRED is available and available but disabled.
As a result, when FRED is available but disabled, its IDT handler
is not installed thus spurious_interrupt() will be invoked.

Fix it by parsing cmdline param "fred=" in cpu_parse_early_param()
to minimize the gap between FRED is available and available but
disabled.

Fixes: 3810da12710a ("x86/fred: Add a fred= cmdline param")
Reported-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
---

Change since v1:
* Use strncmp() instead of strcmp().
---
 arch/x86/kernel/cpu/common.c |  5 +++++
 arch/x86/kernel/traps.c      | 26 --------------------------
 2 files changed, 5 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index d4e539d4e158..10a5402d8297 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1510,6 +1510,11 @@ static void __init cpu_parse_early_param(void)
 	if (cmdline_find_option_bool(boot_command_line, "nousershstk"))
 		setup_clear_cpu_cap(X86_FEATURE_USER_SHSTK);
 
+	/* Minimize the gap between FRED is available and available but disabled. */
+	arglen = cmdline_find_option(boot_command_line, "fred", arg, sizeof(arg));
+	if (arglen != 2 || strncmp(arg, "on", 2))
+		setup_clear_cpu_cap(X86_FEATURE_FRED);
+
 	arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
 	if (arglen <= 0)
 		return;
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 4fa0b17e5043..6afb41e6cbbb 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1402,34 +1402,8 @@ DEFINE_IDTENTRY_SW(iret_error)
 }
 #endif
 
-/* Do not enable FRED by default yet. */
-static bool enable_fred __ro_after_init = false;
-
-#ifdef CONFIG_X86_FRED
-static int __init fred_setup(char *str)
-{
-	if (!str)
-		return -EINVAL;
-
-	if (!cpu_feature_enabled(X86_FEATURE_FRED))
-		return 0;
-
-	if (!strcmp(str, "on"))
-		enable_fred = true;
-	else if (!strcmp(str, "off"))
-		enable_fred = false;
-	else
-		pr_warn("invalid FRED option: 'fred=%s'\n", str);
-	return 0;
-}
-early_param("fred", fred_setup);
-#endif
-
 void __init trap_init(void)
 {
-	if (cpu_feature_enabled(X86_FEATURE_FRED) && !enable_fred)
-		setup_clear_cpu_cap(X86_FEATURE_FRED);
-
 	/* Init cpu_entry_area before IST entries are set up */
 	setup_cpu_entry_areas();
 
-- 
2.45.2