• Tim Chen's avatar
    x86/speculation: Prepare for per task indirect branch speculation control · 5bfbe3ad
    Tim Chen authored
    To avoid the overhead of STIBP always on, it's necessary to allow per task
    control of STIBP.
    
    Add a new task flag TIF_SPEC_IB and evaluate it during context switch if
    SMT is active and flag evaluation is enabled by the speculation control
    code. Add the conditional evaluation to x86_virt_spec_ctrl() as well so the
    guest/host switch works properly.
    
    This has no effect because TIF_SPEC_IB cannot be set yet and the static key
    which controls evaluation is off. Preparatory patch for adding the control
    code.
    
    [ tglx: Simplify the context switch logic and make the TIF evaluation
      	depend on SMP=y and on the static key controlling the conditional
      	update. Rename it to TIF_SPEC_IB because it controls both STIBP and
      	IBPB ]
    Signed-off-by: default avatarTim Chen <tim.c.chen@linux.intel.com>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Reviewed-by: Ingo Molnar's avatarIngo Molnar <mingo@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Jiri Kosina <jkosina@suse.cz>
    Cc: Tom Lendacky <thomas.lendacky@amd.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: David Woodhouse <dwmw@amazon.co.uk>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: Dave Hansen <dave.hansen@intel.com>
    Cc: Casey Schaufler <casey.schaufler@intel.com>
    Cc: Asit Mallick <asit.k.mallick@intel.com>
    Cc: Arjan van de Ven <arjan@linux.intel.com>
    Cc: Jon Masters <jcm@redhat.com>
    Cc: Waiman Long <longman9394@gmail.com>
    Cc: Greg KH <gregkh@linuxfoundation.org>
    Cc: Dave Stewart <david.c.stewart@intel.com>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: stable@vger.kernel.org
    Link: https://lkml.kernel.org/r/20181125185005.176917199@linutronix.de
    
    5bfbe3ad
msr-index.h 29.1 KB