Merge branch kvm-arm64/stage2-vhe-load into kvmarm/next

* kvm-arm64/stage2-vhe-load:
  : Setup stage-2 MMU from vcpu_load() for VHE
  :
  : Unlike nVHE, there is no need to switch the stage-2 MMU around on guest
  : entry/exit in VHE mode as the host is running at EL2. Despite this KVM
  : reloads the stage-2 on every guest entry, which is needless.
  :
  : This series moves the setup of the stage-2 MMU context to vcpu_load()
  : when running in VHE mode. This is likely to be a win across the board,
  : but also allows us to remove an ISB on the guest entry path for systems
  : with one of the speculative AT errata.
  KVM: arm64: Move VTCR_EL2 into struct s2_mmu
  KVM: arm64: Load the stage-2 MMU context in kvm_vcpu_load_vhe()
  KVM: arm64: Rename helpers for VHE vCPU load/put
  KVM: arm64: Reload stage-2 for VMID change on VHE
  KVM: arm64: Restore the stage-2 context in VHE's __tlb_switch_to_host()
  KVM: arm64: Don't zero VTTBR in __tlb_switch_to_host()
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/include/asm/kvm_host.h

@@ -158,6 +158,16 @@ struct kvm_s2_mmu {
 	phys_addr_t	pgd_phys;
 	struct kvm_pgtable *pgt;
 
+	/*
+	 * VTCR value used on the host. For a non-NV guest (or a NV
+	 * guest that runs in a context where its own S2 doesn't
+	 * apply), its T0SZ value reflects that of the IPA size.
+	 *
+	 * For a shadow S2 MMU, T0SZ reflects the PARange exposed to
+	 * the guest.
+	 */
+	u64	vtcr;
+
 	/* The last vcpu id that ran on each physical CPU */
 	int __percpu *last_vcpu_ran;
 
@@ -205,9 +215,6 @@ struct kvm_protected_vm {
 struct kvm_arch {
 	struct kvm_s2_mmu mmu;
 
-	/* VTCR_EL2 value for this VM */
-	u64    vtcr;
-
 	/* Interrupt controller */
 	struct vgic_dist	vgic;
 
@@ -1020,7 +1027,7 @@ int kvm_arm_pvtime_has_attr(struct kvm_vcpu *vcpu,
 extern unsigned int __ro_after_init kvm_arm_vmid_bits;
 int __init kvm_arm_vmid_alloc_init(void);
 void __init kvm_arm_vmid_alloc_free(void);
-void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid);
+bool kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid);
 void kvm_arm_vmid_clear_active(void);
 
 static inline void kvm_arm_pvtime_vcpu_init(struct kvm_vcpu_arch *vcpu_arch)
@@ -1104,8 +1111,8 @@ static inline bool kvm_set_pmuserenr(u64 val)
 }
 #endif
 
-void kvm_vcpu_load_sysregs_vhe(struct kvm_vcpu *vcpu);
-void kvm_vcpu_put_sysregs_vhe(struct kvm_vcpu *vcpu);
+void kvm_vcpu_load_vhe(struct kvm_vcpu *vcpu);
+void kvm_vcpu_put_vhe(struct kvm_vcpu *vcpu);
 
 int __init kvm_set_ipa_limit(void);
 

arch/arm64/include/asm/kvm_hyp.h

@@ -93,6 +93,8 @@ void __timer_disable_traps(struct kvm_vcpu *vcpu);
 void __sysreg_save_state_nvhe(struct kvm_cpu_context *ctxt);
 void __sysreg_restore_state_nvhe(struct kvm_cpu_context *ctxt);
 #else
+void __vcpu_load_switch_sysregs(struct kvm_vcpu *vcpu);
+void __vcpu_put_switch_sysregs(struct kvm_vcpu *vcpu);
 void sysreg_save_host_state_vhe(struct kvm_cpu_context *ctxt);
 void sysreg_restore_host_state_vhe(struct kvm_cpu_context *ctxt);
 void sysreg_save_guest_state_vhe(struct kvm_cpu_context *ctxt);
@@ -111,11 +113,6 @@ void __fpsimd_save_state(struct user_fpsimd_state *fp_regs);
 void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs);
 void __sve_restore_state(void *sve_pffr, u32 *fpsr);
 
-#ifndef __KVM_NVHE_HYPERVISOR__
-void activate_traps_vhe_load(struct kvm_vcpu *vcpu);
-void deactivate_traps_vhe_put(struct kvm_vcpu *vcpu);
-#endif
-
 u64 __guest_enter(struct kvm_vcpu *vcpu);
 
 bool kvm_host_psci_handler(struct kvm_cpu_context *host_ctxt, u32 func_id);

arch/arm64/include/asm/kvm_mmu.h

@@ -150,9 +150,9 @@ static __always_inline unsigned long __kern_hyp_va(unsigned long v)
  */
 #define KVM_PHYS_SHIFT	(40)
 
-#define kvm_phys_shift(kvm)		VTCR_EL2_IPA(kvm->arch.vtcr)
-#define kvm_phys_size(kvm)		(_AC(1, ULL) << kvm_phys_shift(kvm))
-#define kvm_phys_mask(kvm)		(kvm_phys_size(kvm) - _AC(1, ULL))
+#define kvm_phys_shift(mmu)		VTCR_EL2_IPA((mmu)->vtcr)
+#define kvm_phys_size(mmu)		(_AC(1, ULL) << kvm_phys_shift(mmu))
+#define kvm_phys_mask(mmu)		(kvm_phys_size(mmu) - _AC(1, ULL))
 
 #include <asm/kvm_pgtable.h>
 #include <asm/stage2_pgtable.h>
@@ -324,7 +324,7 @@ static __always_inline u64 kvm_get_vttbr(struct kvm_s2_mmu *mmu)
 static __always_inline void __load_stage2(struct kvm_s2_mmu *mmu,
 					  struct kvm_arch *arch)
 {
-	write_sysreg(arch->vtcr, vtcr_el2);
+	write_sysreg(mmu->vtcr, vtcr_el2);
 	write_sysreg(kvm_get_vttbr(mmu), vttbr_el2);
 
 	/*

arch/arm64/include/asm/stage2_pgtable.h

@@ -21,13 +21,13 @@
  * (IPA_SHIFT - 4).
  */
 #define stage2_pgtable_levels(ipa)	ARM64_HW_PGTABLE_LEVELS((ipa) - 4)
-#define kvm_stage2_levels(kvm)		VTCR_EL2_LVLS(kvm->arch.vtcr)
+#define kvm_stage2_levels(mmu)		VTCR_EL2_LVLS((mmu)->vtcr)
 
 /*
  * kvm_mmmu_cache_min_pages() is the number of pages required to install
  * a stage-2 translation. We pre-allocate the entry level page table at
  * the VM creation.
  */
-#define kvm_mmu_cache_min_pages(kvm)	(kvm_stage2_levels(kvm) - 1)
+#define kvm_mmu_cache_min_pages(mmu)	(kvm_stage2_levels(mmu) - 1)
 
 #endif	/* __ARM64_S2_PGTABLE_H_ */

arch/arm64/kvm/arm.c

@@ -447,7 +447,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	kvm_vgic_load(vcpu);
 	kvm_timer_vcpu_load(vcpu);
 	if (has_vhe())
-		kvm_vcpu_load_sysregs_vhe(vcpu);
+		kvm_vcpu_load_vhe(vcpu);
 	kvm_arch_vcpu_load_fp(vcpu);
 	kvm_vcpu_pmu_restore_guest(vcpu);
 	if (kvm_arm_is_pvtime_enabled(&vcpu->arch))
@@ -471,7 +471,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 	kvm_arch_vcpu_put_debug_state_flags(vcpu);
 	kvm_arch_vcpu_put_fp(vcpu);
 	if (has_vhe())
-		kvm_vcpu_put_sysregs_vhe(vcpu);
+		kvm_vcpu_put_vhe(vcpu);
 	kvm_timer_vcpu_put(vcpu);
 	kvm_vgic_put(vcpu);
 	kvm_vcpu_pmu_restore_host(vcpu);
@@ -949,7 +949,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 		 * making a thread's VMID inactive. So we need to call
 		 * kvm_arm_vmid_update() in non-premptible context.
 		 */
-		kvm_arm_vmid_update(&vcpu->arch.hw_mmu->vmid);
+		if (kvm_arm_vmid_update(&vcpu->arch.hw_mmu->vmid) &&
+		    has_vhe())
+			__load_stage2(vcpu->arch.hw_mmu,
+				      vcpu->arch.hw_mmu->arch);
 
 		kvm_pmu_flush_hwstate(vcpu);
 

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

@@ -129,7 +129,7 @@ static void prepare_host_vtcr(void)
 	parange = kvm_get_parange(id_aa64mmfr0_el1_sys_val);
 	phys_shift = id_aa64mmfr0_parange_to_phys_shift(parange);
 
-	host_mmu.arch.vtcr = kvm_get_vtcr(id_aa64mmfr0_el1_sys_val,
+	host_mmu.arch.mmu.vtcr = kvm_get_vtcr(id_aa64mmfr0_el1_sys_val,
 					      id_aa64mmfr1_el1_sys_val, phys_shift);
 }
 
@@ -235,7 +235,7 @@ int kvm_guest_prepare_stage2(struct pkvm_hyp_vm *vm, void *pgd)
 	unsigned long nr_pages;
 	int ret;
 
-	nr_pages = kvm_pgtable_stage2_pgd_size(vm->kvm.arch.vtcr) >> PAGE_SHIFT;
+	nr_pages = kvm_pgtable_stage2_pgd_size(mmu->vtcr) >> PAGE_SHIFT;
 	ret = hyp_pool_init(&vm->pool, hyp_virt_to_pfn(pgd), nr_pages, 0);
 	if (ret)
 		return ret;
@@ -295,7 +295,7 @@ int __pkvm_prot_finalize(void)
 		return -EPERM;
 
 	params->vttbr = kvm_get_vttbr(mmu);
-	params->vtcr = host_mmu.arch.vtcr;
+	params->vtcr = mmu->vtcr;
 	params->hcr_el2 |= HCR_VM;
 
 	/*

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

@@ -303,7 +303,7 @@ static void init_pkvm_hyp_vm(struct kvm *host_kvm, struct pkvm_hyp_vm *hyp_vm,
 {
 	hyp_vm->host_kvm = host_kvm;
 	hyp_vm->kvm.created_vcpus = nr_vcpus;
-	hyp_vm->kvm.arch.vtcr = host_mmu.arch.vtcr;
+	hyp_vm->kvm.arch.mmu.vtcr = host_mmu.arch.mmu.vtcr;
 }
 
 static int init_pkvm_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu,
@@ -483,7 +483,7 @@ int __pkvm_init_vm(struct kvm *host_kvm, unsigned long vm_hva,
 	}
 
 	vm_size = pkvm_get_hyp_vm_size(nr_vcpus);
-	pgd_size = kvm_pgtable_stage2_pgd_size(host_mmu.arch.vtcr);
+	pgd_size = kvm_pgtable_stage2_pgd_size(host_mmu.arch.mmu.vtcr);
 
 	ret = -ENOMEM;
 

arch/arm64/kvm/hyp/pgtable.c

@@ -1511,7 +1511,7 @@ int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
 			      kvm_pgtable_force_pte_cb_t force_pte_cb)
 {
 	size_t pgd_sz;
-	u64 vtcr = mmu->arch->vtcr;
+	u64 vtcr = mmu->vtcr;
 	u32 ia_bits = VTCR_EL2_IPA(vtcr);
 	u32 sl0 = FIELD_GET(VTCR_EL2_SL0_MASK, vtcr);
 	u32 start_level = VTCR_EL2_TGRAN_SL0_BASE - sl0;

arch/arm64/kvm/hyp/vhe/switch.c

@@ -93,12 +93,12 @@ static void __deactivate_traps(struct kvm_vcpu *vcpu)
 NOKPROBE_SYMBOL(__deactivate_traps);
 
 /*
- * Disable IRQs in {activate,deactivate}_traps_vhe_{load,put}() to
+ * Disable IRQs in __vcpu_{load,put}_{activate,deactivate}_traps() to
  * prevent a race condition between context switching of PMUSERENR_EL0
  * in __{activate,deactivate}_traps_common() and IPIs that attempts to
  * update PMUSERENR_EL0. See also kvm_set_pmuserenr().
  */
-void activate_traps_vhe_load(struct kvm_vcpu *vcpu)
+static void __vcpu_load_activate_traps(struct kvm_vcpu *vcpu)
 {
 	unsigned long flags;
 
@@ -107,7 +107,7 @@ void activate_traps_vhe_load(struct kvm_vcpu *vcpu)
 	local_irq_restore(flags);
 }
 
-void deactivate_traps_vhe_put(struct kvm_vcpu *vcpu)
+static void __vcpu_put_deactivate_traps(struct kvm_vcpu *vcpu)
 {
 	unsigned long flags;
 
@@ -116,6 +116,19 @@ void deactivate_traps_vhe_put(struct kvm_vcpu *vcpu)
 	local_irq_restore(flags);
 }
 
+void kvm_vcpu_load_vhe(struct kvm_vcpu *vcpu)
+{
+	__vcpu_load_switch_sysregs(vcpu);
+	__vcpu_load_activate_traps(vcpu);
+	__load_stage2(vcpu->arch.hw_mmu, vcpu->arch.hw_mmu->arch);
+}
+
+void kvm_vcpu_put_vhe(struct kvm_vcpu *vcpu)
+{
+	__vcpu_put_deactivate_traps(vcpu);
+	__vcpu_put_switch_sysregs(vcpu);
+}
+
 static const exit_handler_fn hyp_exit_handlers[] = {
 	[0 ... ESR_ELx_EC_MAX]		= NULL,
 	[ESR_ELx_EC_CP15_32]		= kvm_hyp_handle_cp15_32,
@@ -170,17 +183,11 @@ static int __kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
 	sysreg_save_host_state_vhe(host_ctxt);
 
 	/*
-	 * ARM erratum 1165522 requires us to configure both stage 1 and
-	 * stage 2 translation for the guest context before we clear
-	 * HCR_EL2.TGE.
-	 *
-	 * We have already configured the guest's stage 1 translation in
-	 * kvm_vcpu_load_sysregs_vhe above.  We must now call
-	 * __load_stage2 before __activate_traps, because
-	 * __load_stage2 configures stage 2 translation, and
-	 * __activate_traps clear HCR_EL2.TGE (among other things).
+	 * Note that ARM erratum 1165522 requires us to configure both stage 1
+	 * and stage 2 translation for the guest context before we clear
+	 * HCR_EL2.TGE. The stage 1 and stage 2 guest context has already been
+	 * loaded on the CPU in kvm_vcpu_load_vhe().
 	 */
-	__load_stage2(vcpu->arch.hw_mmu, vcpu->arch.hw_mmu->arch);
 	__activate_traps(vcpu);
 
 	__kvm_adjust_pc(vcpu);

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

@@ -52,7 +52,7 @@ void sysreg_restore_guest_state_vhe(struct kvm_cpu_context *ctxt)
 NOKPROBE_SYMBOL(sysreg_restore_guest_state_vhe);
 
 /**
- * kvm_vcpu_load_sysregs_vhe - Load guest system registers to the physical CPU
+ * __vcpu_load_switch_sysregs - Load guest system registers to the physical CPU
  *
  * @vcpu: The VCPU pointer
  *
@@ -62,7 +62,7 @@ NOKPROBE_SYMBOL(sysreg_restore_guest_state_vhe);
  * and loading system register state early avoids having to load them on
  * every entry to the VM.
  */
-void kvm_vcpu_load_sysregs_vhe(struct kvm_vcpu *vcpu)
+void __vcpu_load_switch_sysregs(struct kvm_vcpu *vcpu)
 {
 	struct kvm_cpu_context *guest_ctxt = &vcpu->arch.ctxt;
 	struct kvm_cpu_context *host_ctxt;
@@ -92,12 +92,10 @@ void kvm_vcpu_load_sysregs_vhe(struct kvm_vcpu *vcpu)
 	__sysreg_restore_el1_state(guest_ctxt);
 
 	vcpu_set_flag(vcpu, SYSREGS_ON_CPU);
-
-	activate_traps_vhe_load(vcpu);
 }
 
 /**
- * kvm_vcpu_put_sysregs_vhe - Restore host system registers to the physical CPU
+ * __vcpu_put_switch_syregs - Restore host system registers to the physical CPU
  *
  * @vcpu: The VCPU pointer
  *
@@ -107,13 +105,12 @@ void kvm_vcpu_load_sysregs_vhe(struct kvm_vcpu *vcpu)
  * and deferring saving system register state until we're no longer running the
  * VCPU avoids having to save them on every exit from the VM.
  */
-void kvm_vcpu_put_sysregs_vhe(struct kvm_vcpu *vcpu)
+void __vcpu_put_switch_sysregs(struct kvm_vcpu *vcpu)
 {
 	struct kvm_cpu_context *guest_ctxt = &vcpu->arch.ctxt;
 	struct kvm_cpu_context *host_ctxt;
 
 	host_ctxt = &this_cpu_ptr(&kvm_host_data)->host_ctxt;
-	deactivate_traps_vhe_put(vcpu);
 
 	__sysreg_save_el1_state(guest_ctxt);
 	__sysreg_save_user_state(guest_ctxt);

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

@@ -11,6 +11,7 @@
 #include <asm/tlbflush.h>
 
 struct tlb_inv_context {
+	struct kvm_s2_mmu	*mmu;
 	unsigned long		flags;
 	u64			tcr;
 	u64			sctlr;
@@ -19,10 +20,16 @@ struct tlb_inv_context {
 static void __tlb_switch_to_guest(struct kvm_s2_mmu *mmu,
 				  struct tlb_inv_context *cxt)
 {
+	struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
 	u64 val;
 
 	local_irq_save(cxt->flags);
 
+	if (vcpu && mmu != vcpu->arch.hw_mmu)
+		cxt->mmu = vcpu->arch.hw_mmu;
+	else
+		cxt->mmu = NULL;
+
 	if (cpus_have_final_cap(ARM64_WORKAROUND_SPECULATIVE_AT)) {
 		/*
 		 * For CPUs that are affected by ARM errata 1165522 or 1530923,
@@ -66,10 +73,13 @@ static void __tlb_switch_to_host(struct tlb_inv_context *cxt)
 	 * We're done with the TLB operation, let's restore the host's
 	 * view of HCR_EL2.
 	 */
-	write_sysreg(0, vttbr_el2);
 	write_sysreg(HCR_HOST_VHE_FLAGS, hcr_el2);
 	isb();
 
+	/* ... and the stage-2 MMU context that we switched away from */
+	if (cxt->mmu)
+		__load_stage2(cxt->mmu, cxt->mmu->arch);
+
 	if (cpus_have_final_cap(ARM64_WORKAROUND_SPECULATIVE_AT)) {
 		/* Restore the registers to what they were */
 		write_sysreg_el1(cxt->tcr, SYS_TCR);

arch/arm64/kvm/mmu.c

@@ -892,7 +892,7 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long t
 
 	mmfr0 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR0_EL1);
 	mmfr1 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR1_EL1);
-	kvm->arch.vtcr = kvm_get_vtcr(mmfr0, mmfr1, phys_shift);
+	mmu->vtcr = kvm_get_vtcr(mmfr0, mmfr1, phys_shift);
 
 	if (mmu->pgt != NULL) {
 		kvm_err("kvm_arch already initialized?\n");
@@ -1067,7 +1067,8 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
 	phys_addr_t addr;
 	int ret = 0;
 	struct kvm_mmu_memory_cache cache = { .gfp_zero = __GFP_ZERO };
-	struct kvm_pgtable *pgt = kvm->arch.mmu.pgt;
+	struct kvm_s2_mmu *mmu = &kvm->arch.mmu;
+	struct kvm_pgtable *pgt = mmu->pgt;
 	enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_DEVICE |
 				     KVM_PGTABLE_PROT_R |
 				     (writable ? KVM_PGTABLE_PROT_W : 0);
@@ -1080,7 +1081,7 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
 
 	for (addr = guest_ipa; addr < guest_ipa + size; addr += PAGE_SIZE) {
 		ret = kvm_mmu_topup_memory_cache(&cache,
-						 kvm_mmu_cache_min_pages(kvm));
+						 kvm_mmu_cache_min_pages(mmu));
 		if (ret)
 			break;
 
@@ -1411,7 +1412,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	if (fault_status != ESR_ELx_FSC_PERM ||
 	    (logging_active && write_fault)) {
 		ret = kvm_mmu_topup_memory_cache(memcache,
-						 kvm_mmu_cache_min_pages(kvm));
+						 kvm_mmu_cache_min_pages(vcpu->arch.hw_mmu));
 		if (ret)
 			return ret;
 	}
@@ -1727,7 +1728,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 	}
 
 	/* Userspace should not be able to register out-of-bounds IPAs */
-	VM_BUG_ON(fault_ipa >= kvm_phys_size(vcpu->kvm));
+	VM_BUG_ON(fault_ipa >= kvm_phys_size(vcpu->arch.hw_mmu));
 
 	if (fault_status == ESR_ELx_FSC_ACCESS) {
 		handle_access_fault(vcpu, fault_ipa);
@@ -2001,7 +2002,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	 * Prevent userspace from creating a memory region outside of the IPA
 	 * space addressable by the KVM guest IPA space.
 	 */
-	if ((new->base_gfn + new->npages) > (kvm_phys_size(kvm) >> PAGE_SHIFT))
+	if ((new->base_gfn + new->npages) > (kvm_phys_size(&kvm->arch.mmu) >> PAGE_SHIFT))
 		return -EFAULT;
 
 	hva = new->userspace_addr;

arch/arm64/kvm/pkvm.c

@@ -123,7 +123,7 @@ static int __pkvm_create_hyp_vm(struct kvm *host_kvm)
 	if (host_kvm->created_vcpus < 1)
 		return -EINVAL;
 
-	pgd_sz = kvm_pgtable_stage2_pgd_size(host_kvm->arch.vtcr);
+	pgd_sz = kvm_pgtable_stage2_pgd_size(host_kvm->arch.mmu.vtcr);
 
 	/*
 	 * The PGD pages will be reclaimed using a hyp_memcache which implies

arch/arm64/kvm/vgic/vgic-kvm-device.c

@@ -27,7 +27,8 @@ int vgic_check_iorange(struct kvm *kvm, phys_addr_t ioaddr,
 	if (addr + size < addr)
 		return -EINVAL;
 
-	if (addr & ~kvm_phys_mask(kvm) || addr + size > kvm_phys_size(kvm))
+	if (addr & ~kvm_phys_mask(&kvm->arch.mmu) ||
+	    (addr + size) > kvm_phys_size(&kvm->arch.mmu))
 		return -E2BIG;
 
 	return 0;

arch/arm64/kvm/vmid.c

@@ -135,10 +135,11 @@ void kvm_arm_vmid_clear_active(void)
 	atomic64_set(this_cpu_ptr(&active_vmids), VMID_ACTIVE_INVALID);
 }
 
-void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid)
+bool kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid)
 {
 	unsigned long flags;
 	u64 vmid, old_active_vmid;
+	bool updated = false;
 
 	vmid = atomic64_read(&kvm_vmid->id);
 
@@ -156,17 +157,21 @@ void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid)
 	if (old_active_vmid != 0 && vmid_gen_match(vmid) &&
 	    0 != atomic64_cmpxchg_relaxed(this_cpu_ptr(&active_vmids),
 					  old_active_vmid, vmid))
-		return;
+		return false;
 
 	raw_spin_lock_irqsave(&cpu_vmid_lock, flags);
 
 	/* Check that our VMID belongs to the current generation. */
 	vmid = atomic64_read(&kvm_vmid->id);
-	if (!vmid_gen_match(vmid))
+	if (!vmid_gen_match(vmid)) {
 		vmid = new_vmid(kvm_vmid);
+		updated = true;
+	}
 
 	atomic64_set(this_cpu_ptr(&active_vmids), vmid);
 	raw_spin_unlock_irqrestore(&cpu_vmid_lock, flags);
+
+	return updated;
 }
 
 /*