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

Pull more kvm updates from Paolo Bonzini:

 - Xen timer fixes

 - Documentation formatting fixes

 - Make rseq selftest compatible with glibc-2.35

 - Fix handling of illegal LEA reg, reg

 - Cleanup creation of debugfs entries

 - Fix steal time cache handling bug

 - Fixes for MMIO caching

 - Optimize computation of number of LBRs

 - Fix uninitialized field in guest_maxphyaddr < host_maxphyaddr path

* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (26 commits)
  KVM: x86/MMU: properly format KVM_CAP_VM_DISABLE_NX_HUGE_PAGES capability table
  Documentation: KVM: extend KVM_CAP_VM_DISABLE_NX_HUGE_PAGES heading underline
  KVM: VMX: Adjust number of LBR records for PERF_CAPABILITIES at refresh
  KVM: VMX: Use proper type-safe functions for vCPU => LBRs helpers
  KVM: x86: Refresh PMU after writes to MSR_IA32_PERF_CAPABILITIES
  KVM: selftests: Test all possible "invalid" PERF_CAPABILITIES.LBR_FMT vals
  KVM: selftests: Use getcpu() instead of sched_getcpu() in rseq_test
  KVM: selftests: Make rseq compatible with glibc-2.35
  KVM: Actually create debugfs in kvm_create_vm()
  KVM: Pass the name of the VM fd to kvm_create_vm_debugfs()
  KVM: Get an fd before creating the VM
  KVM: Shove vcpu stats_id init into kvm_vcpu_init()
  KVM: Shove vm stats_id init into kvm_create_vm()
  KVM: x86/mmu: Add sanity check that MMIO SPTE mask doesn't overlap gen
  KVM: x86/mmu: rename trace function name for asynchronous page fault
  KVM: x86/xen: Stop Xen timer before changing IRQ
  KVM: x86/xen: Initialize Xen timer only once
  KVM: SVM: Disable SEV-ES support if MMIO caching is disable
  KVM: x86/mmu: Fully re-evaluate MMIO caching when SPTE masks change
  KVM: x86: Tag kvm_mmu_x86_module_init() with __init
  ...

13 files changed, 125 insertions, 50 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index e8281d64a431..5ffa578cafe1 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1704,7 +1704,7 @@ static inline int kvm_arch_flush_remote_tlb(struct kvm *kvm)
 #define kvm_arch_pmi_in_guest(vcpu) \
 	((vcpu) && (vcpu)->arch.handling_intr_from_guest)
 
-void kvm_mmu_x86_module_init(void);
+void __init kvm_mmu_x86_module_init(void);
 int kvm_mmu_vendor_module_init(void);
 void kvm_mmu_vendor_module_exit(void);
 
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 047c583596bb..b4eeb7c75dfa 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4578,6 +4578,10 @@ static const struct mode_dual mode_dual_63 = {
 	N, I(DstReg | SrcMem32 | ModRM | Mov, em_movsxd)
 };
 
+static const struct instr_dual instr_dual_8d = {
+	D(DstReg | SrcMem | ModRM | NoAccess), N
+};
+
 static const struct opcode opcode_table[256] = {
 	/* 0x00 - 0x07 */
 	F6ALU(Lock, em_add),
@@ -4634,7 +4638,7 @@ static const struct opcode opcode_table[256] = {
 	I2bv(DstMem | SrcReg | ModRM | Mov | PageTable, em_mov),
 	I2bv(DstReg | SrcMem | ModRM | Mov, em_mov),
 	I(DstMem | SrcNone | ModRM | Mov | PageTable, em_mov_rm_sreg),
-	D(ModRM | SrcMem | NoAccess | DstReg),
+	ID(0, &instr_dual_8d),
 	I(ImplicitOps | SrcMem16 | ModRM, em_mov_sreg_rm),
 	G(0, group1A),
 	/* 0x90 - 0x97 */
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index e2ce3556915e..9dda989a1cf0 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2284,10 +2284,12 @@ void kvm_apic_write_nodecode(struct kvm_vcpu *vcpu, u32 offset)
 	struct kvm_lapic *apic = vcpu->arch.apic;
 	u64 val;
 
-	if (apic_x2apic_mode(apic))
-		kvm_lapic_msr_read(apic, offset, &val);
-	else
+	if (apic_x2apic_mode(apic)) {
+		if (KVM_BUG_ON(kvm_lapic_msr_read(apic, offset, &val), vcpu->kvm))
+			return;
+	} else {
 		val = kvm_lapic_get_reg(apic, offset);
+	}
 
 	/*
 	 * ICR is a single 64-bit register when x2APIC is enabled.  For legacy
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index a99acec925eb..6bdaacb6faa0 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -6,6 +6,8 @@
 #include "kvm_cache_regs.h"
 #include "cpuid.h"
 
+extern bool __read_mostly enable_mmio_caching;
+
 #define PT_WRITABLE_SHIFT 1
 #define PT_USER_SHIFT 2
 
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 06ac8c7cef67..eccddb136954 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4164,7 +4164,7 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 	if (!fault->prefetch && kvm_can_do_async_pf(vcpu)) {
 		trace_kvm_try_async_get_page(fault->addr, fault->gfn);
 		if (kvm_find_async_pf_gfn(vcpu, fault->gfn)) {
-			trace_kvm_async_pf_doublefault(fault->addr, fault->gfn);
+			trace_kvm_async_pf_repeated_fault(fault->addr, fault->gfn);
 			kvm_make_request(KVM_REQ_APF_HALT, vcpu);
 			return RET_PF_RETRY;
 		} else if (kvm_arch_setup_async_pf(vcpu, fault->addr, fault->gfn)) {
@@ -6697,11 +6697,15 @@ static int set_nx_huge_pages(const char *val, const struct kernel_param *kp)
 /*
  * nx_huge_pages needs to be resolved to true/false when kvm.ko is loaded, as
  * its default value of -1 is technically undefined behavior for a boolean.
+ * Forward the module init call to SPTE code so that it too can handle module
+ * params that need to be resolved/snapshot.
  */
-void kvm_mmu_x86_module_init(void)
+void __init kvm_mmu_x86_module_init(void)
 {
 	if (nx_huge_pages == -1)
 		__set_nx_huge_pages(get_nx_auto_mode());
+
+	kvm_mmu_spte_module_init();
 }
 
 /*
diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index 7314d27d57a4..2e08b2a45361 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -20,7 +20,9 @@
 #include <asm/vmx.h>
 
 bool __read_mostly enable_mmio_caching = true;
+static bool __ro_after_init allow_mmio_caching;
 module_param_named(mmio_caching, enable_mmio_caching, bool, 0444);
+EXPORT_SYMBOL_GPL(enable_mmio_caching);
 
 u64 __read_mostly shadow_host_writable_mask;
 u64 __read_mostly shadow_mmu_writable_mask;
@@ -43,6 +45,18 @@ u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask;
 
 u8 __read_mostly shadow_phys_bits;
 
+void __init kvm_mmu_spte_module_init(void)
+{
+	/*
+	 * Snapshot userspace's desire to allow MMIO caching.  Whether or not
+	 * KVM can actually enable MMIO caching depends on vendor-specific
+	 * hardware capabilities and other module params that can't be resolved
+	 * until the vendor module is loaded, i.e. enable_mmio_caching can and
+	 * will change when the vendor module is (re)loaded.
+	 */
+	allow_mmio_caching = enable_mmio_caching;
+}
+
 static u64 generation_mmio_spte_mask(u64 gen)
 {
 	u64 mask;
@@ -340,10 +354,24 @@ void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask)
 	BUG_ON((u64)(unsigned)access_mask != access_mask);
 	WARN_ON(mmio_value & shadow_nonpresent_or_rsvd_lower_gfn_mask);
 
+	/*
+	 * Reset to the original module param value to honor userspace's desire
+	 * to (dis)allow MMIO caching.  Update the param itself so that
+	 * userspace can see whether or not KVM is actually using MMIO caching.
+	 */
+	enable_mmio_caching = allow_mmio_caching;
 	if (!enable_mmio_caching)
 		mmio_value = 0;
 
 	/*
+	 * The mask must contain only bits that are carved out specifically for
+	 * the MMIO SPTE mask, e.g. to ensure there's no overlap with the MMIO
+	 * generation.
+	 */
+	if (WARN_ON(mmio_mask & ~SPTE_MMIO_ALLOWED_MASK))
+		mmio_value = 0;
+
+	/*
 	 * Disable MMIO caching if the MMIO value collides with the bits that
 	 * are used to hold the relocated GFN when the L1TF mitigation is
 	 * enabled.  This should never fire as there is no known hardware that
diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index cabe3fbb4f39..f3744eea45f5 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -5,8 +5,6 @@
 
 #include "mmu_internal.h"
 
-extern bool __read_mostly enable_mmio_caching;
-
 /*
  * A MMU present SPTE is backed by actual memory and may or may not be present
  * in hardware.  E.g. MMIO SPTEs are not considered present.  Use bit 11, as it
@@ -125,6 +123,20 @@ static_assert(!(EPT_SPTE_MMU_WRITABLE & SHADOW_ACC_TRACK_SAVED_MASK));
 static_assert(!(SPTE_MMU_PRESENT_MASK &
 		(MMIO_SPTE_GEN_LOW_MASK | MMIO_SPTE_GEN_HIGH_MASK)));
 
+/*
+ * The SPTE MMIO mask must NOT overlap the MMIO generation bits or the
+ * MMU-present bit.  The generation obviously co-exists with the magic MMIO
+ * mask/value, and MMIO SPTEs are considered !MMU-present.
+ *
+ * The SPTE MMIO mask is allowed to use hardware "present" bits (i.e. all EPT
+ * RWX bits), all physical address bits (legal PA bits are used for "fast" MMIO
+ * and so they're off-limits for generation; additional checks ensure the mask
+ * doesn't overlap legal PA bits), and bit 63 (carved out for future usage).
+ */
+#define SPTE_MMIO_ALLOWED_MASK (BIT_ULL(63) | GENMASK_ULL(51, 12) | GENMASK_ULL(2, 0))
+static_assert(!(SPTE_MMIO_ALLOWED_MASK &
+		(SPTE_MMU_PRESENT_MASK | MMIO_SPTE_GEN_LOW_MASK | MMIO_SPTE_GEN_HIGH_MASK)));
+
 #define MMIO_SPTE_GEN_LOW_BITS		(MMIO_SPTE_GEN_LOW_END - MMIO_SPTE_GEN_LOW_START + 1)
 #define MMIO_SPTE_GEN_HIGH_BITS		(MMIO_SPTE_GEN_HIGH_END - MMIO_SPTE_GEN_HIGH_START + 1)
 
@@ -450,6 +462,7 @@ static inline u64 restore_acc_track_spte(u64 spte)
 
 u64 kvm_mmu_changed_pte_notifier_make_spte(u64 old_spte, kvm_pfn_t new_pfn);
 
+void __init kvm_mmu_spte_module_init(void);
 void kvm_mmu_reset_all_pte_masks(void);
 
 #endif
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index b0e793e7d85c..28064060413a 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -22,6 +22,7 @@
 #include <asm/trapnr.h>
 #include <asm/fpu/xcr.h>
 
+#include "mmu.h"
 #include "x86.h"
 #include "svm.h"
 #include "svm_ops.h"
@@ -2221,6 +2222,15 @@ void __init sev_hardware_setup(void)
 	if (!sev_es_enabled)
 		goto out;
 
+	/*
+	 * SEV-ES requires MMIO caching as KVM doesn't have access to the guest
+	 * instruction stream, i.e. can't emulate in response to a #NPF and
+	 * instead relies on #NPF(RSVD) being reflected into the guest as #VC
+	 * (the guest can then do a #VMGEXIT to request MMIO emulation).
+	 */
+	if (!enable_mmio_caching)
+		goto out;
+
 	/* Does the CPU support SEV-ES? */
 	if (!boot_cpu_has(X86_FEATURE_SEV_ES))
 		goto out;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 38f873cb6f2c..f3813dbacb9f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5034,13 +5034,16 @@ static __init int svm_hardware_setup(void)
 	/* Setup shadow_me_value and shadow_me_mask */
 	kvm_mmu_set_me_spte_mask(sme_me_mask, sme_me_mask);
 
-	/* Note, SEV setup consumes npt_enabled. */
+	svm_adjust_mmio_mask();
+
+	/*
+	 * Note, SEV setup consumes npt_enabled and enable_mmio_caching (which
+	 * may be modified by svm_adjust_mmio_mask()).
+	 */
 	sev_hardware_setup();
 
 	svm_hv_hardware_setup();
 
-	svm_adjust_mmio_mask();
-
 	for_each_possible_cpu(cpu) {
 		r = svm_cpu_init(cpu);
 		if (r)
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 862c1a4d971b..c399637a3a79 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -171,13 +171,6 @@ static inline struct kvm_pmc *get_fw_gp_pmc(struct kvm_pmu *pmu, u32 msr)
 	return get_gp_pmc(pmu, msr, MSR_IA32_PMC0);
 }
 
-bool intel_pmu_lbr_is_enabled(struct kvm_vcpu *vcpu)
-{
-	struct x86_pmu_lbr *lbr = vcpu_to_lbr_records(vcpu);
-
-	return lbr->nr && (vcpu_get_perf_capabilities(vcpu) & PMU_CAP_LBR_FMT);
-}
-
 static bool intel_pmu_is_valid_lbr_msr(struct kvm_vcpu *vcpu, u32 index)
 {
 	struct x86_pmu_lbr *records = vcpu_to_lbr_records(vcpu);
@@ -592,7 +585,9 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
 	bitmap_set(pmu->all_valid_pmc_idx,
 		INTEL_PMC_MAX_GENERIC, pmu->nr_arch_fixed_counters);
 
-	if (cpuid_model_is_consistent(vcpu))
+	perf_capabilities = vcpu_get_perf_capabilities(vcpu);
+	if (cpuid_model_is_consistent(vcpu) &&
+	    (perf_capabilities & PMU_CAP_LBR_FMT))
 		x86_perf_get_lbr(&lbr_desc->records);
 	else
 		lbr_desc->records.nr = 0;
@@ -600,7 +595,6 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
 	if (lbr_desc->records.nr)
 		bitmap_set(pmu->all_valid_pmc_idx, INTEL_PMC_IDX_FIXED_VLBR, 1);
 
-	perf_capabilities = vcpu_get_perf_capabilities(vcpu);
 	if (perf_capabilities & PERF_CAP_PEBS_FORMAT) {
 		if (perf_capabilities & PERF_CAP_PEBS_BASELINE) {
 			pmu->pebs_enable_mask = counter_mask;
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index fb8e3480a9d7..24d58c2ffaa3 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -6,6 +6,7 @@
 
 #include <asm/kvm.h>
 #include <asm/intel_pt.h>
+#include <asm/perf_event.h>
 
 #include "capabilities.h"
 #include "../kvm_cache_regs.h"
@@ -104,15 +105,6 @@ static inline bool intel_pmu_has_perf_global_ctrl(struct kvm_pmu *pmu)
 	return pmu->version > 1;
 }
 
-#define vcpu_to_lbr_desc(vcpu) (&to_vmx(vcpu)->lbr_desc)
-#define vcpu_to_lbr_records(vcpu) (&to_vmx(vcpu)->lbr_desc.records)
-
-void intel_pmu_cross_mapped_check(struct kvm_pmu *pmu);
-bool intel_pmu_lbr_is_enabled(struct kvm_vcpu *vcpu);
-
-int intel_pmu_create_guest_lbr_event(struct kvm_vcpu *vcpu);
-void vmx_passthrough_lbr_msrs(struct kvm_vcpu *vcpu);
-
 struct lbr_desc {
 	/* Basic info about guest LBR records. */
 	struct x86_pmu_lbr records;
@@ -542,6 +534,25 @@ static inline struct vcpu_vmx *to_vmx(struct kvm_vcpu *vcpu)
 	return container_of(vcpu, struct vcpu_vmx, vcpu);
 }
 
+static inline struct lbr_desc *vcpu_to_lbr_desc(struct kvm_vcpu *vcpu)
+{
+	return &to_vmx(vcpu)->lbr_desc;
+}
+
+static inline struct x86_pmu_lbr *vcpu_to_lbr_records(struct kvm_vcpu *vcpu)
+{
+	return &vcpu_to_lbr_desc(vcpu)->records;
+}
+
+static inline bool intel_pmu_lbr_is_enabled(struct kvm_vcpu *vcpu)
+{
+	return !!vcpu_to_lbr_records(vcpu)->nr;
+}
+
+void intel_pmu_cross_mapped_check(struct kvm_pmu *pmu);
+int intel_pmu_create_guest_lbr_event(struct kvm_vcpu *vcpu);
+void vmx_passthrough_lbr_msrs(struct kvm_vcpu *vcpu);
+
 static inline unsigned long vmx_get_exit_qual(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 79a8a74b6b2a..205ebdc2b11b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3413,6 +3413,7 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
 	struct gfn_to_hva_cache *ghc = &vcpu->arch.st.cache;
 	struct kvm_steal_time __user *st;
 	struct kvm_memslots *slots;
+	gpa_t gpa = vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS;
 	u64 steal;
 	u32 version;
 
@@ -3430,13 +3431,12 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
 	slots = kvm_memslots(vcpu->kvm);
 
 	if (unlikely(slots->generation != ghc->generation ||
+		     gpa != ghc->gpa ||
 		     kvm_is_error_hva(ghc->hva) || !ghc->memslot)) {
-		gfn_t gfn = vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS;
-
 		/* We rely on the fact that it fits in a single page. */
 		BUILD_BUG_ON((sizeof(*st) - 1) & KVM_STEAL_VALID_BITS);
 
-		if (kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, gfn, sizeof(*st)) ||
+		if (kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, gpa, sizeof(*st)) ||
 		    kvm_is_error_hva(ghc->hva) || !ghc->memslot)
 			return;
 	}
@@ -3545,9 +3545,9 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			return 1;
 
 		vcpu->arch.perf_capabilities = data;
-
+		kvm_pmu_refresh(vcpu);
 		return 0;
-		}
+	}
 	case MSR_EFER:
 		return set_efer(vcpu, msr_info);
 	case MSR_K7_HWCR:
@@ -4714,6 +4714,7 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
 	struct kvm_steal_time __user *st;
 	struct kvm_memslots *slots;
 	static const u8 preempted = KVM_VCPU_PREEMPTED;
+	gpa_t gpa = vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS;
 
 	/*
 	 * The vCPU can be marked preempted if and only if the VM-Exit was on
@@ -4741,6 +4742,7 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
 	slots = kvm_memslots(vcpu->kvm);
 
 	if (unlikely(slots->generation != ghc->generation ||
+		     gpa != ghc->gpa ||
 		     kvm_is_error_hva(ghc->hva) || !ghc->memslot))
 		return;
 
@@ -13019,6 +13021,7 @@ void kvm_fixup_and_inject_pf_error(struct kvm_vcpu *vcpu, gva_t gva, u16 error_c
 		fault.error_code = error_code;
 		fault.nested_page_fault = false;
 		fault.address = gva;
+		fault.async_page_fault = false;
 	}
 	vcpu->arch.walk_mmu->inject_page_fault(vcpu, &fault);
 }
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index a0c05ccbf4b1..280cb5dc7341 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -707,23 +707,24 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
 		break;
 
 	case KVM_XEN_VCPU_ATTR_TYPE_TIMER:
-		if (data->u.timer.port) {
-			if (data->u.timer.priority != KVM_IRQ_ROUTING_XEN_EVTCHN_PRIO_2LEVEL) {
-				r = -EINVAL;
-				break;
-			}
-			vcpu->arch.xen.timer_virq = data->u.timer.port;
+		if (data->u.timer.port &&
+		    data->u.timer.priority != KVM_IRQ_ROUTING_XEN_EVTCHN_PRIO_2LEVEL) {
+			r = -EINVAL;
+			break;
+		}
+
+		if (!vcpu->arch.xen.timer.function)
 			kvm_xen_init_timer(vcpu);
 
-			/* Restart the timer if it's set */
-			if (data->u.timer.expires_ns)
-				kvm_xen_start_timer(vcpu, data->u.timer.expires_ns,
-						    data->u.timer.expires_ns -
-						    get_kvmclock_ns(vcpu->kvm));
-		} else if (kvm_xen_timer_enabled(vcpu)) {
-			kvm_xen_stop_timer(vcpu);
-			vcpu->arch.xen.timer_virq = 0;
-		}
+		/* Stop the timer (if it's running) before changing the vector */
+		kvm_xen_stop_timer(vcpu);
+		vcpu->arch.xen.timer_virq = data->u.timer.port;
+
+		/* Start the timer if the new value has a valid vector+expiry. */
+		if (data->u.timer.port && data->u.timer.expires_ns)
+			kvm_xen_start_timer(vcpu, data->u.timer.expires_ns,
+					    data->u.timer.expires_ns -
+					    get_kvmclock_ns(vcpu->kvm));
 
 		r = 0;
 		break;