x86/speculation: Prepare for per task indirect branch speculation control

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: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo 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

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/x86/include/asm/spec-ctrl.h b/arch/x86/include/asm/spec-ctrl.h
index 8e2f8411c7a7..27b0bce3933b 100644
--- a/arch/x86/include/asm/spec-ctrl.h
+++ b/arch/x86/include/asm/spec-ctrl.h
@@ -53,12 +53,24 @@ static inline u64 ssbd_tif_to_spec_ctrl(u64 tifn)
 	return (tifn & _TIF_SSBD) >> (TIF_SSBD - SPEC_CTRL_SSBD_SHIFT);
 }
 
+static inline u64 stibp_tif_to_spec_ctrl(u64 tifn)
+{
+	BUILD_BUG_ON(TIF_SPEC_IB < SPEC_CTRL_STIBP_SHIFT);
+	return (tifn & _TIF_SPEC_IB) >> (TIF_SPEC_IB - SPEC_CTRL_STIBP_SHIFT);
+}
+
 static inline unsigned long ssbd_spec_ctrl_to_tif(u64 spec_ctrl)
 {
 	BUILD_BUG_ON(TIF_SSBD < SPEC_CTRL_SSBD_SHIFT);
 	return (spec_ctrl & SPEC_CTRL_SSBD) << (TIF_SSBD - SPEC_CTRL_SSBD_SHIFT);
 }
 
+static inline unsigned long stibp_spec_ctrl_to_tif(u64 spec_ctrl)
+{
+	BUILD_BUG_ON(TIF_SPEC_IB < SPEC_CTRL_STIBP_SHIFT);
+	return (spec_ctrl & SPEC_CTRL_STIBP) << (TIF_SPEC_IB - SPEC_CTRL_STIBP_SHIFT);
+}
+
 static inline u64 ssbd_tif_to_amd_ls_cfg(u64 tifn)
 {
 	return (tifn & _TIF_SSBD) ? x86_amd_ls_cfg_ssbd_mask : 0ULL;