Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

Pull kvm fixes from Paolo Bonzini:

 -  x86 bugfixes

 - Documentation fixes

 - Avoid performance regression due to SEV-ES patches

 - ARM:
     - Don't allow tagged pointers to point to memslots
     - Filter out ARMv8.1+ PMU events on v8.0 hardware
     - Hide PMU registers from userspace when no PMU is configured
     - More PMU cleanups
     - Don't try to handle broken PSCI firmware
     - More sys_reg() to reg_to_encoding() conversions

* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  KVM: x86: allow KVM_REQ_GET_NESTED_STATE_PAGES outside guest mode for VMX
  KVM: x86: Revert "KVM: x86: Mark GPRs dirty when written"
  KVM: SVM: Unconditionally sync GPRs to GHCB on VMRUN of SEV-ES guest
  KVM: nVMX: Sync unsync'd vmcs02 state to vmcs12 on migration
  kvm: tracing: Fix unmatched kvm_entry and kvm_exit events
  KVM: Documentation: Update description of KVM_{GET,CLEAR}_DIRTY_LOG
  KVM: x86: get smi pending status correctly
  KVM: x86/pmu: Fix HW_REF_CPU_CYCLES event pseudo-encoding in intel_arch_events[]
  KVM: x86/pmu: Fix UBSAN shift-out-of-bounds warning in intel_pmu_refresh()
  KVM: x86: Add more protection against undefined behavior in rsvd_bits()
  KVM: Documentation: Fix spec for KVM_CAP_ENABLE_CAP_VM
  KVM: Forbid the use of tagged userspace addresses for memslots
  KVM: arm64: Filter out v8.1+ events on v8.0 HW
  KVM: arm64: Compute TPIDR_EL2 ignoring MTE tag
  KVM: arm64: Use the reg_to_encoding() macro instead of sys_reg()
  KVM: arm64: Allow PSCI SYSTEM_OFF/RESET to return
  KVM: arm64: Simplify handling of absent PMU system registers
  KVM: arm64: Hide PMU registers from userspace when not available

Author: torvalds

Documentation/virt/kvm/api.rst

@@ -360,10 +360,9 @@ since the last call to this ioctl.  Bit 0 is the first page in the
 memory slot.  Ensure the entire structure is cleared to avoid padding
 issues.
 
-If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 specifies
-the address space for which you want to return the dirty bitmap.
-They must be less than the value that KVM_CHECK_EXTENSION returns for
-the KVM_CAP_MULTI_ADDRESS_SPACE capability.
+If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 of slot field specifies
+the address space for which you want to return the dirty bitmap.  See
+KVM_SET_USER_MEMORY_REGION for details on the usage of slot field.
 
 The bits in the dirty bitmap are cleared before the ioctl returns, unless
 KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is enabled.  For more information,
@@ -1281,6 +1280,9 @@ field userspace_addr, which must point at user addressable memory for
 the entire memory slot size.  Any object may back this memory, including
 anonymous memory, ordinary files, and hugetlbfs.
 
+On architectures that support a form of address tagging, userspace_addr must
+be an untagged address.
+
 It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
 be identical.  This allows large pages in the guest to be backed by large
 pages in the host.
@@ -1333,7 +1335,7 @@ documentation when it pops into existence).
 
 :Capability: KVM_CAP_ENABLE_CAP_VM
 :Architectures: all
-:Type: vcpu ioctl
+:Type: vm ioctl
 :Parameters: struct kvm_enable_cap (in)
 :Returns: 0 on success; -1 on error
 
@@ -4432,7 +4434,7 @@ to I/O ports.
 :Capability: KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2
 :Architectures: x86, arm, arm64, mips
 :Type: vm ioctl
-:Parameters: struct kvm_dirty_log (in)
+:Parameters: struct kvm_clear_dirty_log (in)
 :Returns: 0 on success, -1 on error
 
 ::
@@ -4459,10 +4461,9 @@ in KVM's dirty bitmap, and dirty tracking is re-enabled for that page
 (for example via write-protection, or by clearing the dirty bit in
 a page table entry).
 
-If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 specifies
-the address space for which you want to return the dirty bitmap.
-They must be less than the value that KVM_CHECK_EXTENSION returns for
-the KVM_CAP_MULTI_ADDRESS_SPACE capability.
+If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 of slot field specifies
+the address space for which you want to clear the dirty status.  See
+KVM_SET_USER_MEMORY_REGION for details on the usage of slot field.
 
 This ioctl is mostly useful when KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2
 is enabled; for more information, see the description of the capability.

arch/arm64/kvm/arm.c

@@ -1396,8 +1396,9 @@ static void cpu_init_hyp_mode(void)
 	 * Calculate the raw per-cpu offset without a translation from the
 	 * kernel's mapping to the linear mapping, and store it in tpidr_el2
 	 * so that we can use adr_l to access per-cpu variables in EL2.
+	 * Also drop the KASAN tag which gets in the way...
 	 */
-	params->tpidr_el2 = (unsigned long)this_cpu_ptr_nvhe_sym(__per_cpu_start) -
+	params->tpidr_el2 = (unsigned long)kasan_reset_tag(this_cpu_ptr_nvhe_sym(__per_cpu_start)) -
 			    (unsigned long)kvm_ksym_ref(CHOOSE_NVHE_SYM(__per_cpu_start));
 
 	params->mair_el2 = read_sysreg(mair_el1);

arch/arm64/kvm/hyp/nvhe/psci-relay.c

@@ -77,12 +77,6 @@ static unsigned long psci_forward(struct kvm_cpu_context *host_ctxt)
 			 cpu_reg(host_ctxt, 2), cpu_reg(host_ctxt, 3));
 }
 
-static __noreturn unsigned long psci_forward_noreturn(struct kvm_cpu_context *host_ctxt)
-{
-	psci_forward(host_ctxt);
-	hyp_panic(); /* unreachable */
-}
-
 static unsigned int find_cpu_id(u64 mpidr)
 {
 	unsigned int i;
@@ -251,10 +245,13 @@ static unsigned long psci_0_2_handler(u64 func_id, struct kvm_cpu_context *host_
 	case PSCI_0_2_FN_MIGRATE_INFO_TYPE:
 	case PSCI_0_2_FN64_MIGRATE_INFO_UP_CPU:
 		return psci_forward(host_ctxt);
+	/*
+	 * SYSTEM_OFF/RESET should not return according to the spec.
+	 * Allow it so as to stay robust to broken firmware.
+	 */
 	case PSCI_0_2_FN_SYSTEM_OFF:
 	case PSCI_0_2_FN_SYSTEM_RESET:
-		psci_forward_noreturn(host_ctxt);
-		unreachable();
+		return psci_forward(host_ctxt);
 	case PSCI_0_2_FN64_CPU_SUSPEND:
 		return psci_cpu_suspend(func_id, host_ctxt);
 	case PSCI_0_2_FN64_CPU_ON:

arch/arm64/kvm/pmu-emul.c

@@ -788,7 +788,7 @@ u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1)
 {
 	unsigned long *bmap = vcpu->kvm->arch.pmu_filter;
 	u64 val, mask = 0;
-	int base, i;
+	int base, i, nr_events;
 
 	if (!pmceid1) {
 		val = read_sysreg(pmceid0_el0);
@@ -801,13 +801,17 @@ u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1)
 	if (!bmap)
 		return val;
 
+	nr_events = kvm_pmu_event_mask(vcpu->kvm) + 1;
+
 	for (i = 0; i < 32; i += 8) {
 		u64 byte;
 
 		byte = bitmap_get_value8(bmap, base + i);
 		mask |= byte << i;
-		byte = bitmap_get_value8(bmap, 0x4000 + base + i);
-		mask |= byte << (32 + i);
+		if (nr_events >= (0x4000 + base + 32)) {
+			byte = bitmap_get_value8(bmap, 0x4000 + base + i);
+			mask |= byte << (32 + i);
+		}
 	}
 
 	return val & mask;

arch/arm64/kvm/sys_regs.c

@@ -43,6 +43,10 @@
  * 64bit interface.
  */
 
+#define reg_to_encoding(x)						\
+	sys_reg((u32)(x)->Op0, (u32)(x)->Op1,				\
+		(u32)(x)->CRn, (u32)(x)->CRm, (u32)(x)->Op2)
+
 static bool read_from_write_only(struct kvm_vcpu *vcpu,
 				 struct sys_reg_params *params,
 				 const struct sys_reg_desc *r)
@@ -273,8 +277,7 @@ static bool trap_loregion(struct kvm_vcpu *vcpu,
 			  const struct sys_reg_desc *r)
 {
 	u64 val = read_sanitised_ftr_reg(SYS_ID_AA64MMFR1_EL1);
-	u32 sr = sys_reg((u32)r->Op0, (u32)r->Op1,
-			 (u32)r->CRn, (u32)r->CRm, (u32)r->Op2);
+	u32 sr = reg_to_encoding(r);
 
 	if (!(val & (0xfUL << ID_AA64MMFR1_LOR_SHIFT))) {
 		kvm_inject_undefined(vcpu);
@@ -590,6 +593,15 @@ static void reset_mpidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
 	vcpu_write_sys_reg(vcpu, (1ULL << 31) | mpidr, MPIDR_EL1);
 }
 
+static unsigned int pmu_visibility(const struct kvm_vcpu *vcpu,
+				   const struct sys_reg_desc *r)
+{
+	if (kvm_vcpu_has_pmu(vcpu))
+		return 0;
+
+	return REG_HIDDEN;
+}
+
 static void reset_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
 {
 	u64 pmcr, val;
@@ -613,9 +625,8 @@ static void reset_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
 static bool check_pmu_access_disabled(struct kvm_vcpu *vcpu, u64 flags)
 {
 	u64 reg = __vcpu_sys_reg(vcpu, PMUSERENR_EL0);
-	bool enabled = kvm_vcpu_has_pmu(vcpu);
+	bool enabled = (reg & flags) || vcpu_mode_priv(vcpu);
 
-	enabled &= (reg & flags) || vcpu_mode_priv(vcpu);
 	if (!enabled)
 		kvm_inject_undefined(vcpu);
 
@@ -900,11 +911,6 @@ static bool access_pmswinc(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 static bool access_pmuserenr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 			     const struct sys_reg_desc *r)
 {
-	if (!kvm_vcpu_has_pmu(vcpu)) {
-		kvm_inject_undefined(vcpu);
-		return false;
-	}
-
 	if (p->is_write) {
 		if (!vcpu_mode_priv(vcpu)) {
 			kvm_inject_undefined(vcpu);
@@ -921,10 +927,6 @@ static bool access_pmuserenr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 	return true;
 }
 
-#define reg_to_encoding(x)						\
-	sys_reg((u32)(x)->Op0, (u32)(x)->Op1,				\
-		(u32)(x)->CRn, (u32)(x)->CRm, (u32)(x)->Op2)
-
 /* Silly macro to expand the DBG{BCR,BVR,WVR,WCR}n_EL1 registers in one go */
 #define DBG_BCR_BVR_WCR_WVR_EL1(n)					\
 	{ SYS_DESC(SYS_DBGBVRn_EL1(n)),					\
@@ -936,15 +938,18 @@ static bool access_pmuserenr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 	{ SYS_DESC(SYS_DBGWCRn_EL1(n)),					\
 	  trap_wcr, reset_wcr, 0, 0,  get_wcr, set_wcr }
 
+#define PMU_SYS_REG(r)						\
+	SYS_DESC(r), .reset = reset_unknown, .visibility = pmu_visibility
+
 /* Macro to expand the PMEVCNTRn_EL0 register */
 #define PMU_PMEVCNTR_EL0(n)						\
-	{ SYS_DESC(SYS_PMEVCNTRn_EL0(n)),					\
-	  access_pmu_evcntr, reset_unknown, (PMEVCNTR0_EL0 + n), }
+	{ PMU_SYS_REG(SYS_PMEVCNTRn_EL0(n)),				\
+	  .access = access_pmu_evcntr, .reg = (PMEVCNTR0_EL0 + n), }
 
 /* Macro to expand the PMEVTYPERn_EL0 register */
 #define PMU_PMEVTYPER_EL0(n)						\
-	{ SYS_DESC(SYS_PMEVTYPERn_EL0(n)),					\
-	  access_pmu_evtyper, reset_unknown, (PMEVTYPER0_EL0 + n), }
+	{ PMU_SYS_REG(SYS_PMEVTYPERn_EL0(n)),				\
+	  .access = access_pmu_evtyper, .reg = (PMEVTYPER0_EL0 + n), }
 
 static bool undef_access(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 			 const struct sys_reg_desc *r)
@@ -1020,8 +1025,7 @@ static bool access_arch_timer(struct kvm_vcpu *vcpu,
 static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 		struct sys_reg_desc const *r, bool raz)
 {
-	u32 id = sys_reg((u32)r->Op0, (u32)r->Op1,
-			 (u32)r->CRn, (u32)r->CRm, (u32)r->Op2);
+	u32 id = reg_to_encoding(r);
 	u64 val = raz ? 0 : read_sanitised_ftr_reg(id);
 
 	if (id == SYS_ID_AA64PFR0_EL1) {
@@ -1062,8 +1066,7 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 static unsigned int id_visibility(const struct kvm_vcpu *vcpu,
 				  const struct sys_reg_desc *r)
 {
-	u32 id = sys_reg((u32)r->Op0, (u32)r->Op1,
-			 (u32)r->CRn, (u32)r->CRm, (u32)r->Op2);
+	u32 id = reg_to_encoding(r);
 
 	switch (id) {
 	case SYS_ID_AA64ZFR0_EL1:
@@ -1486,8 +1489,10 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	{ SYS_DESC(SYS_FAR_EL1), access_vm_reg, reset_unknown, FAR_EL1 },
 	{ SYS_DESC(SYS_PAR_EL1), NULL, reset_unknown, PAR_EL1 },
 
-	{ SYS_DESC(SYS_PMINTENSET_EL1), access_pminten, reset_unknown, PMINTENSET_EL1 },
-	{ SYS_DESC(SYS_PMINTENCLR_EL1), access_pminten, reset_unknown, PMINTENSET_EL1 },
+	{ PMU_SYS_REG(SYS_PMINTENSET_EL1),
+	  .access = access_pminten, .reg = PMINTENSET_EL1 },
+	{ PMU_SYS_REG(SYS_PMINTENCLR_EL1),
+	  .access = access_pminten, .reg = PMINTENSET_EL1 },
 
 	{ SYS_DESC(SYS_MAIR_EL1), access_vm_reg, reset_unknown, MAIR_EL1 },
 	{ SYS_DESC(SYS_AMAIR_EL1), access_vm_reg, reset_amair_el1, AMAIR_EL1 },
@@ -1526,23 +1531,36 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	{ SYS_DESC(SYS_CSSELR_EL1), access_csselr, reset_unknown, CSSELR_EL1 },
 	{ SYS_DESC(SYS_CTR_EL0), access_ctr },
 
-	{ SYS_DESC(SYS_PMCR_EL0), access_pmcr, reset_pmcr, PMCR_EL0 },
-	{ SYS_DESC(SYS_PMCNTENSET_EL0), access_pmcnten, reset_unknown, PMCNTENSET_EL0 },
-	{ SYS_DESC(SYS_PMCNTENCLR_EL0), access_pmcnten, reset_unknown, PMCNTENSET_EL0 },
-	{ SYS_DESC(SYS_PMOVSCLR_EL0), access_pmovs, reset_unknown, PMOVSSET_EL0 },
-	{ SYS_DESC(SYS_PMSWINC_EL0), access_pmswinc, reset_unknown, PMSWINC_EL0 },
-	{ SYS_DESC(SYS_PMSELR_EL0), access_pmselr, reset_unknown, PMSELR_EL0 },
-	{ SYS_DESC(SYS_PMCEID0_EL0), access_pmceid },
-	{ SYS_DESC(SYS_PMCEID1_EL0), access_pmceid },
-	{ SYS_DESC(SYS_PMCCNTR_EL0), access_pmu_evcntr, reset_unknown, PMCCNTR_EL0 },
-	{ SYS_DESC(SYS_PMXEVTYPER_EL0), access_pmu_evtyper },
-	{ SYS_DESC(SYS_PMXEVCNTR_EL0), access_pmu_evcntr },
+	{ PMU_SYS_REG(SYS_PMCR_EL0), .access = access_pmcr,
+	  .reset = reset_pmcr, .reg = PMCR_EL0 },
+	{ PMU_SYS_REG(SYS_PMCNTENSET_EL0),
+	  .access = access_pmcnten, .reg = PMCNTENSET_EL0 },
+	{ PMU_SYS_REG(SYS_PMCNTENCLR_EL0),
+	  .access = access_pmcnten, .reg = PMCNTENSET_EL0 },
+	{ PMU_SYS_REG(SYS_PMOVSCLR_EL0),
+	  .access = access_pmovs, .reg = PMOVSSET_EL0 },
+	{ PMU_SYS_REG(SYS_PMSWINC_EL0),
+	  .access = access_pmswinc, .reg = PMSWINC_EL0 },
+	{ PMU_SYS_REG(SYS_PMSELR_EL0),
+	  .access = access_pmselr, .reg = PMSELR_EL0 },
+	{ PMU_SYS_REG(SYS_PMCEID0_EL0),
+	  .access = access_pmceid, .reset = NULL },
+	{ PMU_SYS_REG(SYS_PMCEID1_EL0),
+	  .access = access_pmceid, .reset = NULL },
+	{ PMU_SYS_REG(SYS_PMCCNTR_EL0),
+	  .access = access_pmu_evcntr, .reg = PMCCNTR_EL0 },
+	{ PMU_SYS_REG(SYS_PMXEVTYPER_EL0),
+	  .access = access_pmu_evtyper, .reset = NULL },
+	{ PMU_SYS_REG(SYS_PMXEVCNTR_EL0),
+	  .access = access_pmu_evcntr, .reset = NULL },
 	/*
 	 * PMUSERENR_EL0 resets as unknown in 64bit mode while it resets as zero
 	 * in 32bit mode. Here we choose to reset it as zero for consistency.
 	 */
-	{ SYS_DESC(SYS_PMUSERENR_EL0), access_pmuserenr, reset_val, PMUSERENR_EL0, 0 },
-	{ SYS_DESC(SYS_PMOVSSET_EL0), access_pmovs, reset_unknown, PMOVSSET_EL0 },
+	{ PMU_SYS_REG(SYS_PMUSERENR_EL0), .access = access_pmuserenr,
+	  .reset = reset_val, .reg = PMUSERENR_EL0, .val = 0 },
+	{ PMU_SYS_REG(SYS_PMOVSSET_EL0),
+	  .access = access_pmovs, .reg = PMOVSSET_EL0 },
 
 	{ SYS_DESC(SYS_TPIDR_EL0), NULL, reset_unknown, TPIDR_EL0 },
 	{ SYS_DESC(SYS_TPIDRRO_EL0), NULL, reset_unknown, TPIDRRO_EL0 },
@@ -1694,7 +1712,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	 * PMCCFILTR_EL0 resets as unknown in 64bit mode while it resets as zero
 	 * in 32bit mode. Here we choose to reset it as zero for consistency.
 	 */
-	{ SYS_DESC(SYS_PMCCFILTR_EL0), access_pmu_evtyper, reset_val, PMCCFILTR_EL0, 0 },
+	{ PMU_SYS_REG(SYS_PMCCFILTR_EL0), .access = access_pmu_evtyper,
+	  .reset = reset_val, .reg = PMCCFILTR_EL0, .val = 0 },
 
 	{ SYS_DESC(SYS_DACR32_EL2), NULL, reset_unknown, DACR32_EL2 },
 	{ SYS_DESC(SYS_IFSR32_EL2), NULL, reset_unknown, IFSR32_EL2 },

arch/x86/kvm/kvm_cache_regs.h

@@ -9,31 +9,6 @@
 	(X86_CR4_PVI | X86_CR4_DE | X86_CR4_PCE | X86_CR4_OSFXSR  \
 	 | X86_CR4_OSXMMEXCPT | X86_CR4_PGE | X86_CR4_TSD | X86_CR4_FSGSBASE)
 
-static inline bool kvm_register_is_available(struct kvm_vcpu *vcpu,
-					     enum kvm_reg reg)
-{
-	return test_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
-}
-
-static inline bool kvm_register_is_dirty(struct kvm_vcpu *vcpu,
-					 enum kvm_reg reg)
-{
-	return test_bit(reg, (unsigned long *)&vcpu->arch.regs_dirty);
-}
-
-static inline void kvm_register_mark_available(struct kvm_vcpu *vcpu,
-					       enum kvm_reg reg)
-{
-	__set_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
-}
-
-static inline void kvm_register_mark_dirty(struct kvm_vcpu *vcpu,
-					   enum kvm_reg reg)
-{
-	__set_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
-	__set_bit(reg, (unsigned long *)&vcpu->arch.regs_dirty);
-}
-
 #define BUILD_KVM_GPR_ACCESSORS(lname, uname)				      \
 static __always_inline unsigned long kvm_##lname##_read(struct kvm_vcpu *vcpu)\
 {									      \
@@ -43,7 +18,6 @@ static __always_inline void kvm_##lname##_write(struct kvm_vcpu *vcpu,	      \
 						unsigned long val)	      \
 {									      \
 	vcpu->arch.regs[VCPU_REGS_##uname] = val;			      \
-	kvm_register_mark_dirty(vcpu, VCPU_REGS_##uname);		      \
 }
 BUILD_KVM_GPR_ACCESSORS(rax, RAX)
 BUILD_KVM_GPR_ACCESSORS(rbx, RBX)
@@ -63,6 +37,31 @@ BUILD_KVM_GPR_ACCESSORS(r14, R14)
 BUILD_KVM_GPR_ACCESSORS(r15, R15)
 #endif
 
+static inline bool kvm_register_is_available(struct kvm_vcpu *vcpu,
+					     enum kvm_reg reg)
+{
+	return test_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
+}
+
+static inline bool kvm_register_is_dirty(struct kvm_vcpu *vcpu,
+					 enum kvm_reg reg)
+{
+	return test_bit(reg, (unsigned long *)&vcpu->arch.regs_dirty);
+}
+
+static inline void kvm_register_mark_available(struct kvm_vcpu *vcpu,
+					       enum kvm_reg reg)
+{
+	__set_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
+}
+
+static inline void kvm_register_mark_dirty(struct kvm_vcpu *vcpu,
+					   enum kvm_reg reg)
+{
+	__set_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
+	__set_bit(reg, (unsigned long *)&vcpu->arch.regs_dirty);
+}
+
 static inline unsigned long kvm_register_read(struct kvm_vcpu *vcpu, int reg)
 {
 	if (WARN_ON_ONCE((unsigned int)reg >= NR_VCPU_REGS))