[PATCH v9 36/36] x86/fred: Disable FRED by default in its early stage

[Xin Li <xin3.li@xxxxxxxxx>]

Disable FRED by default in its early stage.

To enable FRED, a new kernel command line option "fred" needs to be added.

Tested-by: Shan Kang <shan.kang@xxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
---

Changes since v7:
* Add a log message when FRED is enabled.
---
 Documentation/admin-guide/kernel-parameters.txt | 4 ++++
 arch/x86/kernel/cpu/common.c                    | 3 +++
 arch/x86/kernel/fred.c                          | 3 +++
 3 files changed, 10 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt 
b/Documentation/admin-guide/kernel-parameters.txt
index a1457995fd41..cb12decfcdc0 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1513,6 +1513,10 @@
                        Warning: use of this parameter will taint the kernel
                        and may cause unknown problems.
 
+       fred
+                       Forcefully enable flexible return and event delivery,
+                       which is otherwise disabled by default.
+
        ftrace=[tracer]
                        [FTRACE] will set and start the specified tracer
                        as early as possible in order to facilitate early
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index b34a8a138755..38cf4f64a56e 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1451,6 +1451,9 @@ static void __init cpu_parse_early_param(void)
        char *argptr = arg, *opt;
        int arglen, taint = 0;
 
+       if (!cmdline_find_option_bool(boot_command_line, "fred"))
+               setup_clear_cpu_cap(X86_FEATURE_FRED);
+
 #ifdef CONFIG_X86_32
        if (cmdline_find_option_bool(boot_command_line, "no387"))
 #ifdef CONFIG_MATH_EMULATION
diff --git a/arch/x86/kernel/fred.c b/arch/x86/kernel/fred.c
index 7fdf79c964a8..a4a726ea9fc2 100644
--- a/arch/x86/kernel/fred.c
+++ b/arch/x86/kernel/fred.c
@@ -8,6 +8,9 @@
 
 void cpu_init_fred_exceptions(void)
 {
+       /* When FRED is enabled by default, this log message may not needed */
+       pr_info("Initialize FRED on CPU%d\n", smp_processor_id());
+
        wrmsrl(MSR_IA32_FRED_CONFIG,
               /* Reserve for CALL emulation */
               FRED_CONFIG_REDZONE |
-- 
2.34.1