[PATCH v17 04/14] KVM: arm64: Ensure GCS memory effects are visible

[Mark Brown]

In order to allow efficient implementation of GCS implementations are
permitted to do GCS specific caching, with barriers implicit in stack
switch operations and GCSB DSYNC as an explicit barrier.  Since we do
not use GCS in the hypervisor or host kernel the hypervisor cannot rely
on any barriers being present in vCPU context switches other than those
it explicitly inserts.  Add explicit barriers when loading and saving
vCPU state.

Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
---
 arch/arm64/kvm/hyp/nvhe/switch.c   | 13 +++++++++++++
 arch/arm64/kvm/hyp/vhe/sysreg-sr.c | 14 ++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
index 7318e3e6a5f3..fe8727bf2833 100644
--- a/arch/arm64/kvm/hyp/nvhe/switch.c
+++ b/arch/arm64/kvm/hyp/nvhe/switch.c
@@ -301,6 +301,12 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
 	 */
 	dsb(nsh);
 
+	/*
+	 * Ensure any GCS memory effects are visible to this CPU.
+	 */
+	if (ctxt_has_gcs(guest_ctxt))
+		gcsb_dsync();
+
 	__kvm_adjust_pc(vcpu);
 
 	/*
@@ -345,6 +351,13 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
 	 */
 	dsb(nsh);
 
+	/*
+	 * Ensure any GCS memory effects from the outgoing vCPU are
+	 * visible elsewhere.
+	 */
+	if (ctxt_has_gcs(guest_ctxt))
+		gcsb_dsync();
+
 	__deactivate_traps(vcpu);
 	__load_host_stage2();
 
diff --git a/arch/arm64/kvm/hyp/vhe/sysreg-sr.c b/arch/arm64/kvm/hyp/vhe/sysreg-sr.c
index 2431c18f5792..4594992b008c 100644
--- a/arch/arm64/kvm/hyp/vhe/sysreg-sr.c
+++ b/arch/arm64/kvm/hyp/vhe/sysreg-sr.c
@@ -239,6 +239,13 @@ void __vcpu_load_switch_sysregs(struct kvm_vcpu *vcpu)
 	if (vcpu_has_nv(vcpu))
 		dsb(nsh);
 
+	/*
+	 * Ensure any GCS memory effects are visible to the incoming
+	 * vCPU.
+	 */
+	if (ctxt_has_gcs(guest_ctxt))
+		gcsb_dsync();
+
 	/*
 	 * Load guest EL1 and user state
 	 *
@@ -299,5 +306,12 @@ void __vcpu_put_switch_sysregs(struct kvm_vcpu *vcpu)
 	/* Restore host user state */
 	__sysreg_restore_user_state(host_ctxt);
 
+	/*
+	 * Ensure any GCS memory effects from the outgoing vCPU are
+	 * visible elsewhere.
+	 */
+	if (ctxt_has_gcs(guest_ctxt))
+		gcsb_dsync();
+
 	vcpu_clear_flag(vcpu, SYSREGS_ON_CPU);
 }

-- 
2.47.3