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

commit 7531a3596e3272d1f6841e0d601a614555dc6b65 upstream.

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>
[bwh: Backported to 4.4: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>