KVM: arm64: nvhe: Synchronise with page table walker on TLBI

A TLBI from EL2 impacting EL1 involves messing with the EL1&0
translation regime, and the page table walker may still be
performing speculative walks.

Piggyback on the existing DSBs to always have a DSB ISH that
will synchronise all load/store operations that the PTW may
still have.

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

Author: Marc Zyngier

arch/arm64/kvm/hyp/nvhe/tlb.c

@@ -15,8 +15,31 @@ struct tlb_inv_context {
 };
 
 static void __tlb_switch_to_guest(struct kvm_s2_mmu *mmu,
-				  struct tlb_inv_context *cxt)
+				  struct tlb_inv_context *cxt,
+				  bool nsh)
 {
+	/*
+	 * We have two requirements:
+	 *
+	 * - ensure that the page table updates are visible to all
+	 *   CPUs, for which a dsb(DOMAIN-st) is what we need, DOMAIN
+	 *   being either ish or nsh, depending on the invalidation
+	 *   type.
+	 *
+	 * - complete any speculative page table walk started before
+	 *   we trapped to EL2 so that we can mess with the MM
+	 *   registers out of context, for which dsb(nsh) is enough
+	 *
+	 * The composition of these two barriers is a dsb(DOMAIN), and
+	 * the 'nsh' parameter tracks the distinction between
+	 * Inner-Shareable and Non-Shareable, as specified by the
+	 * callers.
+	 */
+	if (nsh)
+		dsb(nsh);
+	else
+		dsb(ish);
+
 	if (cpus_have_final_cap(ARM64_WORKAROUND_SPECULATIVE_AT)) {
 		u64 val;
 
@@ -60,10 +83,8 @@ void __kvm_tlb_flush_vmid_ipa(struct kvm_s2_mmu *mmu,
 {
 	struct tlb_inv_context cxt;
 
-	dsb(ishst);
-
 	/* Switch to requested VMID */
-	__tlb_switch_to_guest(mmu, &cxt);
+	__tlb_switch_to_guest(mmu, &cxt, false);
 
 	/*
 	 * We could do so much better if we had the VA as well.
@@ -113,10 +134,8 @@ void __kvm_tlb_flush_vmid(struct kvm_s2_mmu *mmu)
 {
 	struct tlb_inv_context cxt;
 
-	dsb(ishst);
-
 	/* Switch to requested VMID */
-	__tlb_switch_to_guest(mmu, &cxt);
+	__tlb_switch_to_guest(mmu, &cxt, false);
 
 	__tlbi(vmalls12e1is);
 	dsb(ish);
@@ -130,7 +149,7 @@ void __kvm_flush_cpu_context(struct kvm_s2_mmu *mmu)
 	struct tlb_inv_context cxt;
 
 	/* Switch to requested VMID */
-	__tlb_switch_to_guest(mmu, &cxt);
+	__tlb_switch_to_guest(mmu, &cxt, false);
 
 	__tlbi(vmalle1);
 	asm volatile("ic iallu");
@@ -142,7 +161,8 @@ void __kvm_flush_cpu_context(struct kvm_s2_mmu *mmu)
 
 void __kvm_flush_vm_context(void)
 {
-	dsb(ishst);
+	/* Same remark as in __tlb_switch_to_guest() */
+	dsb(ish);
 	__tlbi(alle1is);
 
 	/*