From 63f8f8d7fab9b062c581f9c519607b87eccdf54c Mon Sep 17 00:00:00 2001
From: Marc Zyngier <marc.zyngier@arm.com>
Date: Tue, 29 May 2018 13:11:11 +0100
Subject: [PATCH 09/12] arm64: ssbd: Skip apply_ssbd if not using dynamic
 mitigation

Git-commit: 986372c4367f46b34a3c0f6918d7fb95cbdf39d6
Patch-mainline: v4.18-rc1
References: bsc#1085308

In order to avoid checking arm64_ssbd_callback_required on each
kernel entry/exit even if no mitigation is required, let's
add yet another alternative that by default jumps over the mitigation,
and that gets nop'ed out if we're doing dynamic mitigation.

Think of it as a poor man's static key...

Reviewed-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@suse.com>
---
 arch/arm64/kernel/cpu_errata.c | 14 ++++++++++++++
 arch/arm64/kernel/entry.S      |  3 +++
 2 files changed, 17 insertions(+)

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 41613819514a..0f18d03561bf 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -271,6 +271,20 @@ void __init arm64_update_smccc_conduit(struct alt_instr *alt,
 	*updptr = cpu_to_le32(insn);
 }
 
+void __init arm64_enable_wa2_handling(struct alt_instr *alt,
+				      __le32 *origptr, __le32 *updptr,
+				      int nr_inst)
+{
+	BUG_ON(nr_inst != 1);
+	/*
+	 * Only allow mitigation on EL1 entry/exit and guest
+	 * ARCH_WORKAROUND_2 handling if the SSBD state allows it to
+	 * be flipped.
+	 */
+	if (arm64_get_ssbd_state() == ARM64_SSBD_KERNEL)
+		*updptr = cpu_to_le32(aarch64_insn_gen_nop());
+}
+
 static void arm64_set_ssbd_mitigation(bool state)
 {
 	switch (psci_ops.conduit) {
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 8154cc45e325..c43f25a09cbb 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -141,6 +141,9 @@ alternative_else_nop_endif
 	// to save/restore them if required.
 	.macro	apply_ssbd, state, targ, tmp1, tmp2
 #ifdef CONFIG_ARM64_SSBD
+alternative_cb	arm64_enable_wa2_handling
+	b	\targ
+alternative_cb_end
 	ldr_this_cpu	\tmp2, arm64_ssbd_callback_required, \tmp1
 	cbz	\tmp2, \targ
 	mov	w0, #ARM_SMCCC_ARCH_WORKAROUND_2
-- 
2.11.0