x86/fred: Parse cmdline param "fred=" in cpu_parse_early_param()

Depending on whether FRED is enabled, sysvec_install() installs a system
interrupt handler into either into FRED's system vector dispatch table or
into the IDT.

However FRED can be disabled later in trap_init(), after sysvec_install()
has been invoked already; 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, early sysvec_install()
invocations fail to install the IDT handler resulting in spurious
interrupts.

Fix it by parsing cmdline param "fred=" in cpu_parse_early_param() to
ensure that FRED is disabled before the first sysvec_install() incovations.

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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240709154048.3543361-2-xin@zytor.com

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index d4e539d4e158cc561e156c028336080a07478ac8..10a5402d829718ccb7657846684258c42de0f7d0 100644 (file)
--- 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 4fa0b17e5043aa81070fe7716cda5518f808957c..6afb41e6cbbb45da1be2c8af2273251e629f44a0 100644 (file)
--- 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();