powerpc/security: split branch cache flush toggle from code patching

Branch cache flushing code patching has inter-dependencies on both the
link stack and the count cache flushing state.

To make the code clearer and to separate the link stack and count
cache handling, split the "toggle" (setting up variables and printing
enable/disable) from the code patching.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Always print something, even if the flush is disabled]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200609070610.846703-5-npiggin@gmail.com

arch/powerpc/kernel/security.c

@@ -427,61 +427,69 @@ static __init int stf_barrier_debugfs_init(void)
 device_initcall(stf_barrier_debugfs_init);
 #endif /* CONFIG_DEBUG_FS */
 
-static void no_count_cache_flush(void)
+static void update_branch_cache_flush(void)
 {
-	count_cache_flush_type = BRANCH_CACHE_FLUSH_NONE;
-	pr_info("count-cache-flush: flush disabled.\n");
-}
-
-static void toggle_branch_cache_flush(bool enable)
-{
-	if (!security_ftr_enabled(SEC_FTR_FLUSH_COUNT_CACHE) &&
-	    !security_ftr_enabled(SEC_FTR_FLUSH_LINK_STACK))
-		enable = false;
-
-	if (!enable) {
-		patch_instruction_site(&patch__call_flush_branch_caches,
-				       ppc_inst(PPC_INST_NOP));
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
+	// This controls the branch from guest_exit_cont to kvm_flush_link_stack
+	if (link_stack_flush_type == BRANCH_CACHE_FLUSH_NONE) {
 		patch_instruction_site(&patch__call_kvm_flush_link_stack,
 				       ppc_inst(PPC_INST_NOP));
-#endif
-		pr_info("link-stack-flush: flush disabled.\n");
-		link_stack_flush_type = BRANCH_CACHE_FLUSH_NONE;
-		no_count_cache_flush();
-		return;
-	}
-
-	// This enables the branch from _switch to flush_branch_caches
-	patch_branch_site(&patch__call_flush_branch_caches,
-			  (u64)&flush_branch_caches, BRANCH_SET_LINK);
-
-#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
-	// This enables the branch from guest_exit_cont to kvm_flush_link_stack
+	} else {
 		patch_branch_site(&patch__call_kvm_flush_link_stack,
 				  (u64)&kvm_flush_link_stack, BRANCH_SET_LINK);
+	}
 #endif
 
-	pr_info("link-stack-flush: software flush enabled.\n");
-	link_stack_flush_type = BRANCH_CACHE_FLUSH_SW;
+	// This controls the branch from _switch to flush_branch_caches
+	if (count_cache_flush_type == BRANCH_CACHE_FLUSH_NONE &&
+	    link_stack_flush_type == BRANCH_CACHE_FLUSH_NONE) {
+		patch_instruction_site(&patch__call_flush_branch_caches,
+				       ppc_inst(PPC_INST_NOP));
+	} else {
+		patch_branch_site(&patch__call_flush_branch_caches,
+				  (u64)&flush_branch_caches, BRANCH_SET_LINK);
 
-	// If we just need to flush the link stack, patch an early return
-	if (!security_ftr_enabled(SEC_FTR_FLUSH_COUNT_CACHE)) {
+		// If we just need to flush the link stack, early return
+		if (count_cache_flush_type == BRANCH_CACHE_FLUSH_NONE) {
 			patch_instruction_site(&patch__flush_link_stack_return,
 					       ppc_inst(PPC_INST_BLR));
-		no_count_cache_flush();
-		return;
+
+		// If we have flush instruction, early return
+		} else if (count_cache_flush_type == BRANCH_CACHE_FLUSH_HW) {
+			patch_instruction_site(&patch__flush_count_cache_return,
+					       ppc_inst(PPC_INST_BLR));
 		}
+	}
+}
 
-	if (!security_ftr_enabled(SEC_FTR_BCCTR_FLUSH_ASSIST)) {
+static void toggle_branch_cache_flush(bool enable)
+{
+	if (!enable || !security_ftr_enabled(SEC_FTR_FLUSH_COUNT_CACHE)) {
+		if (count_cache_flush_type != BRANCH_CACHE_FLUSH_NONE)
+			count_cache_flush_type = BRANCH_CACHE_FLUSH_NONE;
+
+		pr_info("count-cache-flush: flush disabled.\n");
+	} else {
+		if (security_ftr_enabled(SEC_FTR_BCCTR_FLUSH_ASSIST)) {
+			count_cache_flush_type = BRANCH_CACHE_FLUSH_HW;
+			pr_info("count-cache-flush: hardware flush enabled.\n");
+		} else {
 			count_cache_flush_type = BRANCH_CACHE_FLUSH_SW;
 			pr_info("count-cache-flush: software flush enabled.\n");
-		return;
+		}
 	}
 
-	patch_instruction_site(&patch__flush_count_cache_return, ppc_inst(PPC_INST_BLR));
-	count_cache_flush_type = BRANCH_CACHE_FLUSH_HW;
-	pr_info("count-cache-flush: hardware flush enabled.\n");
+	if (!enable || !security_ftr_enabled(SEC_FTR_FLUSH_LINK_STACK)) {
+		if (link_stack_flush_type != BRANCH_CACHE_FLUSH_NONE)
+			link_stack_flush_type = BRANCH_CACHE_FLUSH_NONE;
+
+		pr_info("link-stack-flush: flush disabled.\n");
+	} else {
+		link_stack_flush_type = BRANCH_CACHE_FLUSH_SW;
+		pr_info("link-stack-flush: software flush enabled.\n");
+	}
+
+	update_branch_cache_flush();
 }
 
 void setup_count_cache_flush(void)