x86/speculation: Reorganize speculation control MSRs update

The logic to detect whether there's a change in the previous and next
task's flag relevant to update speculation control MSRs is spread out
across multiple functions.

Consolidate all checks needed for updating speculation control MSRs into
the new __speculation_ctrl_update() helper function.

This makes it easy to pick the right speculation control MSR and the bits
in MSR_IA32_SPEC_CTRL that need updating based on TIF flags changes.
Originally-by: Thomas Lendacky <Thomas.Lendacky@amd.com>
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/20181125185004.151077005@linutronix.de

arch/x86/kernel/process.c

@@ -395,27 +395,40 @@ static __always_inline void amd_set_ssb_virt_state(unsigned long tifn)
 	wrmsrl(MSR_AMD64_VIRT_SPEC_CTRL, ssbd_tif_to_spec_ctrl(tifn));
 }
 
-static __always_inline void spec_ctrl_update_msr(unsigned long tifn)
+/*
+ * Update the MSRs managing speculation control, during context switch.
+ *
+ * tifp: Previous task's thread flags
+ * tifn: Next task's thread flags
+ */
+static __always_inline void __speculation_ctrl_update(unsigned long tifp,
+						      unsigned long tifn)
 {
-	u64 msr = x86_spec_ctrl_base | ssbd_tif_to_spec_ctrl(tifn);
-
-	wrmsrl(MSR_IA32_SPEC_CTRL, msr);
-}
+	u64 msr = x86_spec_ctrl_base;
+	bool updmsr = false;
 
-static __always_inline void __speculation_ctrl_update(unsigned long tifn)
-{
-	if (static_cpu_has(X86_FEATURE_VIRT_SSBD))
+	/* If TIF_SSBD is different, select the proper mitigation method */
+	if ((tifp ^ tifn) & _TIF_SSBD) {
+		if (static_cpu_has(X86_FEATURE_VIRT_SSBD)) {
 			amd_set_ssb_virt_state(tifn);
-	else if (static_cpu_has(X86_FEATURE_LS_CFG_SSBD))
+		} else if (static_cpu_has(X86_FEATURE_LS_CFG_SSBD)) {
 			amd_set_core_ssb_state(tifn);
-	else
-		spec_ctrl_update_msr(tifn);
+		} else if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) ||
+			   static_cpu_has(X86_FEATURE_AMD_SSBD)) {
+			msr |= ssbd_tif_to_spec_ctrl(tifn);
+			updmsr  = true;
+		}
+	}
+
+	if (updmsr)
+		wrmsrl(MSR_IA32_SPEC_CTRL, msr);
 }
 
 void speculation_ctrl_update(unsigned long tif)
 {
+	/* Forced update. Make sure all relevant TIF flags are different */
 	preempt_disable();
-	__speculation_ctrl_update(tif);
+	__speculation_ctrl_update(~tif, tif);
 	preempt_enable();
 }
 
@@ -451,8 +464,7 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
 	if ((tifp ^ tifn) & _TIF_NOCPUID)
 		set_cpuid_faulting(!!(tifn & _TIF_NOCPUID));
 
-	if ((tifp ^ tifn) & _TIF_SSBD)
-		__speculation_ctrl_update(tifn);
+	__speculation_ctrl_update(tifp, tifn);
 }
 
 /*