KVM: arm64: vhe: Synchronise with page table walker on MMU update

Contrary to nVHE, VHE is a lot easier when it comes to dealing
with speculative page table walks started at EL1. As we only change
EL1&0 translation regime when context-switching, we already benefit
from the effect of the DSB that sits in the context switch code.

We only need to take care of it in the NV case, where we can
flip between between two EL1 contexts (one of them being the virtual
EL2) without a context switch.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>

Author: Marc Zyngier

arch/arm64/kvm/hyp/vhe/sysreg-sr.c

@@ -13,6 +13,7 @@
 #include <asm/kvm_asm.h>
 #include <asm/kvm_emulate.h>
 #include <asm/kvm_hyp.h>
+#include <asm/kvm_nested.h>
 
 /*
  * VHE: Host and guest must save mdscr_el1 and sp_el0 (and the PC and
@@ -69,6 +70,17 @@ void kvm_vcpu_load_sysregs_vhe(struct kvm_vcpu *vcpu)
 	host_ctxt = &this_cpu_ptr(&kvm_host_data)->host_ctxt;
 	__sysreg_save_user_state(host_ctxt);
 
+	/*
+	 * When running a normal EL1 guest, we only load a new vcpu
+	 * after a context switch, which imvolves a DSB, so all
+	 * speculative EL1&0 walks will have already completed.
+	 * If running NV, the vcpu may transition between vEL1 and
+	 * vEL2 without a context switch, so make sure we complete
+	 * those walks before loading a new context.
+	 */
+	if (vcpu_has_nv(vcpu))
+		dsb(nsh);
+
 	/*
 	 * Load guest EL1 and user state
 	 *