x86/tsx: Add "auto" option to the tsx= cmdline parameter

Platforms which are not affected by X86_BUG_TAA may want the TSX feature
enabled. Add "auto" option to the TSX cmdline parameter. When tsx=auto
disable TSX when X86_BUG_TAA is present, otherwise enable TSX.

More details on X86_BUG_TAA can be found here:
https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/tsx_async_abort.html

 [ bp: Extend the arg buffer to accommodate "auto\0". ]

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>

2 files changed, 9 insertions, 1 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index af4b1d95b08f..6e548cddb6c3 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4869,6 +4869,9 @@
                                 update. This new MSR allows for the reliable
                                 deactivation of the TSX functionality.)
 
+                        auto    - Disable TSX if X86_BUG_TAA is present,
+                                  otherwise enable TSX on the system.
+
                         Not specifying this option is equivalent to tsx=off.
 
                         See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c
index 04471c4378d8..dda328ec2ba1 100644
--- a/arch/x86/kernel/cpu/tsx.c
+++ b/arch/x86/kernel/cpu/tsx.c
@@ -75,7 +75,7 @@ static bool __init tsx_ctrl_is_supported(void)
 
 void __init tsx_init(void)
 {
-        char arg[4] = {};
+        char arg[5] = {};
         int ret;
 
         if (!tsx_ctrl_is_supported())
@@ -87,6 +87,11 @@ void __init tsx_init(void)
                         tsx_ctrl_state = TSX_CTRL_ENABLE;
                 } else if (!strcmp(arg, "off")) {
                         tsx_ctrl_state = TSX_CTRL_DISABLE;
+                } else if (!strcmp(arg, "auto")) {
+                        if (boot_cpu_has_bug(X86_BUG_TAA))
+                                tsx_ctrl_state = TSX_CTRL_DISABLE;
+                        else
+                                tsx_ctrl_state = TSX_CTRL_ENABLE;
                 } else {
                         tsx_ctrl_state = TSX_CTRL_DISABLE;
                         pr_err("tsx: invalid option, defaulting to off\n");