[Patch v4 10/18] x86/speculation: Reorganize speculation control MSRs update

[Tim Chen <tim.c.chen@linux.intel.com>]

This patch consolidates checks for prev and next task's flags change
relevant for speculation control MSRs update to __speculation_ctrl_update
function.

This makes it easy to pick the right speculation control MSR,
and the bits in the MSRs that need to be updated based on
TIF_* flags changes.

Originally-by: Thomas Lendacky <Thomas.Lendacky@amd.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 arch/x86/kernel/process.c | 44 +++++++++++++++++++++++++++++++++-----------
 1 file changed, 33 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 8aa4960..74bef48 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -397,25 +397,48 @@ static __always_inline void amd_set_ssb_virt_state(unsigned long tifn)
 
 static __always_inline void spec_ctrl_update_msr(unsigned long tifn)
 {
-	u64 msr = x86_spec_ctrl_base | ssbd_tif_to_spec_ctrl(tifn);
+	u64 msr = x86_spec_ctrl_base;
+
+	/*
+	 * If X86_FEATURE_SSBD is not set, the SSBD
+	 * bit is not to be touched.
+	 */
+	if (static_cpu_has(X86_FEATURE_SSBD))
+		msr |= ssbd_tif_to_spec_ctrl(tifn);
 
 	wrmsrl(MSR_IA32_SPEC_CTRL, msr);
 }
 
-static __always_inline void __speculation_ctrl_update(unsigned long tifn)
-{
-	if (static_cpu_has(X86_FEATURE_VIRT_SSBD))
-		amd_set_ssb_virt_state(tifn);
-	else if (static_cpu_has(X86_FEATURE_LS_CFG_SSBD))
-		amd_set_core_ssb_state(tifn);
-	else
+/*
+ * 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)
+{
+	bool updmsr = false;
+
+	/* 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))
+			amd_set_core_ssb_state(tifn);
+		else if (static_cpu_has(X86_FEATURE_SSBD))
+			updmsr  = true;
+	}
+
+	if (updmsr)
 		spec_ctrl_update_msr(tifn);
 }
 
 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 +474,7 @@ 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);
 }
 
 /*
-- 
2.9.4