From: James Morse <james.morse@arm.com>
Date: Fri, 21 Sep 2018 21:49:19 +0100
Subject: arm64: KVM: Guests can skip __install_bp_hardening_cb()s HYP work

Git-commit: 4debef5510071032c6d5dace31ca1cc42a120073
Patch-mainline: v4.20-rc1
References: bsc#1174547

enable_smccc_arch_workaround_1() passes NULL as the hyp_vecs start and
end if the HVC conduit is in use, and ARM_SMCCC_ARCH_WORKAROUND_1 is
detected.

If the guest kernel happened to be built with KVM_INDIRECT_VECTORS,
we go on to allocate a slot, memcpy() the empty workaround in and
do the appropriate cache maintenance.

This works as we always tell memcpy() the range is 0, so it never
accesses the NULL src pointer, but we still do the cache maintenance.

If hyp_vecs_start is NULL we know we're a guest, just update the fn
like the !KVM_INDIRECT_VECTORS version.

Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mian Yousaf Kaukab <ykaukab@suse.de>
---
 arch/arm64/kernel/cpu_errata.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 9af8df96ec49..a509e35132d2 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -138,6 +138,15 @@ static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
 	static DEFINE_SPINLOCK(bp_lock);
 	int cpu, slot = -1;
 
+	/*
+	 * enable_smccc_arch_workaround_1() passes NULL for the hyp_vecs
+	 * start/end if we're a guest. Skip the hyp-vectors work.
+	 */
+	if (!hyp_vecs_start) {
+		__this_cpu_write(bp_hardening_data.fn, fn);
+		return;
+	}
+
 	spin_lock(&bp_lock);
 	for_each_possible_cpu(cpu) {
 		if (per_cpu(bp_hardening_data.fn, cpu) == fn) {
-- 
2.26.2