KVM: TDX: Handle vCPU dissociation

Handle vCPUs dissociations by invoking SEAMCALL TDH.VP.FLUSH which flushes
the address translation caches and cached TD VMCS of a TD vCPU in its
associated pCPU.

In TDX, a vCPUs can only be associated with one pCPU at a time, which is
done by invoking SEAMCALL TDH.VP.ENTER. For a successful association, the
vCPU must be dissociated from its previous associated pCPU.

To facilitate vCPU dissociation, introduce a per-pCPU list
associated_tdvcpus. Add a vCPU into this list when it's loaded into a new
pCPU (i.e. when a vCPU is loaded for the first time or migrated to a new
pCPU).

vCPU dissociations can happen under below conditions:
- On the op hardware_disable is called.
  This op is called when virtualization is disabled on a given pCPU, e.g.
  when hot-unplug a pCPU or machine shutdown/suspend.
  In this case, dissociate all vCPUs from the pCPU by iterating its
  per-pCPU list associated_tdvcpus.

- On vCPU migration to a new pCPU.
  Before adding a vCPU into associated_tdvcpus list of the new pCPU,
  dissociation from its old pCPU is required, which is performed by issuing
  an IPI and executing SEAMCALL TDH.VP.FLUSH on the old pCPU.
  On a successful dissociation, the vCPU will be removed from the
  associated_tdvcpus list of its previously associated pCPU.

- On tdx_mmu_release_hkid() is called.
  TDX mandates that all vCPUs must be disassociated prior to the release of
  an hkid. Therefore, dissociation of all vCPUs is a must before executing
  the SEAMCALL TDH.MNG.VPFLUSHDONE and subsequently freeing the hkid.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Co-developed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Co-developed-by: Yan Zhao <yan.y.zhao@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Message-ID: <20241112073858.22312-1-yan.y.zhao@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/main.c

@@ -10,6 +10,14 @@
 #include "tdx.h"
 #include "tdx_arch.h"
 
+static void vt_disable_virtualization_cpu(void)
+{
+	/* Note, TDX *and* VMX need to be disabled if TDX is enabled. */
+	if (enable_tdx)
+		tdx_disable_virtualization_cpu();
+	vmx_disable_virtualization_cpu();
+}
+
 static __init int vt_hardware_setup(void)
 {
 	int ret;
@@ -111,6 +119,16 @@ static void vt_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	vmx_vcpu_reset(vcpu, init_event);
 }
 
+static void vt_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
+{
+	if (is_td_vcpu(vcpu)) {
+		tdx_vcpu_load(vcpu, cpu);
+		return;
+	}
+
+	vmx_vcpu_load(vcpu, cpu);
+}
+
 static void vt_flush_tlb_all(struct kvm_vcpu *vcpu)
 {
 	if (is_td_vcpu(vcpu)) {
@@ -199,7 +217,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
 	.hardware_unsetup = vmx_hardware_unsetup,
 
 	.enable_virtualization_cpu = vmx_enable_virtualization_cpu,
-	.disable_virtualization_cpu = vmx_disable_virtualization_cpu,
+	.disable_virtualization_cpu = vt_disable_virtualization_cpu,
 	.emergency_disable_virtualization_cpu = vmx_emergency_disable_virtualization_cpu,
 
 	.has_emulated_msr = vmx_has_emulated_msr,
@@ -216,7 +234,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
 	.vcpu_reset = vt_vcpu_reset,
 
 	.prepare_switch_to_guest = vmx_prepare_switch_to_guest,
-	.vcpu_load = vmx_vcpu_load,
+	.vcpu_load = vt_vcpu_load,
 	.vcpu_put = vmx_vcpu_put,
 
 	.update_exception_bitmap = vmx_update_exception_bitmap,

arch/x86/kvm/vmx/tdx.c

@@ -162,6 +162,21 @@ static bool tdx_operand_busy(u64 err)
 }
 
 
+/*
+ * A per-CPU list of TD vCPUs associated with a given CPU.
+ * Protected by interrupt mask. Only manipulated by the CPU owning this per-CPU
+ * list.
+ * - When a vCPU is loaded onto a CPU, it is removed from the per-CPU list of
+ *   the old CPU during the IPI callback running on the old CPU, and then added
+ *   to the per-CPU list of the new CPU.
+ * - When a TD is tearing down, all vCPUs are disassociated from their current
+ *   running CPUs and removed from the per-CPU list during the IPI callback
+ *   running on those CPUs.
+ * - When a CPU is brought down, traverse the per-CPU list to disassociate all
+ *   associated TD vCPUs and remove them from the per-CPU list.
+ */
+static DEFINE_PER_CPU(struct list_head, associated_tdvcpus);
+
 static inline void tdx_hkid_free(struct kvm_tdx *kvm_tdx)
 {
 	tdx_guest_keyid_free(kvm_tdx->hkid);
@@ -177,6 +192,22 @@ static inline bool is_hkid_assigned(struct kvm_tdx *kvm_tdx)
 	return kvm_tdx->hkid > 0;
 }
 
+static inline void tdx_disassociate_vp(struct kvm_vcpu *vcpu)
+{
+	lockdep_assert_irqs_disabled();
+
+	list_del(&to_tdx(vcpu)->cpu_list);
+
+	/*
+	 * Ensure tdx->cpu_list is updated before setting vcpu->cpu to -1,
+	 * otherwise, a different CPU can see vcpu->cpu = -1 and add the vCPU
+	 * to its list before it's deleted from this CPU's list.
+	 */
+	smp_wmb();
+
+	vcpu->cpu = -1;
+}
+
 static void tdx_clear_page(struct page *page)
 {
 	const void *zero_page = (const void *) page_to_virt(ZERO_PAGE(0));
@@ -243,6 +274,83 @@ static void tdx_reclaim_control_page(struct page *ctrl_page)
 	__free_page(ctrl_page);
 }
 
+struct tdx_flush_vp_arg {
+	struct kvm_vcpu *vcpu;
+	u64 err;
+};
+
+static void tdx_flush_vp(void *_arg)
+{
+	struct tdx_flush_vp_arg *arg = _arg;
+	struct kvm_vcpu *vcpu = arg->vcpu;
+	u64 err;
+
+	arg->err = 0;
+	lockdep_assert_irqs_disabled();
+
+	/* Task migration can race with CPU offlining. */
+	if (unlikely(vcpu->cpu != raw_smp_processor_id()))
+		return;
+
+	/*
+	 * No need to do TDH_VP_FLUSH if the vCPU hasn't been initialized.  The
+	 * list tracking still needs to be updated so that it's correct if/when
+	 * the vCPU does get initialized.
+	 */
+	if (to_tdx(vcpu)->state != VCPU_TD_STATE_UNINITIALIZED) {
+		/*
+		 * No need to retry.  TDX Resources needed for TDH.VP.FLUSH are:
+		 * TDVPR as exclusive, TDR as shared, and TDCS as shared.  This
+		 * vp flush function is called when destructing vCPU/TD or vCPU
+		 * migration.  No other thread uses TDVPR in those cases.
+		 */
+		err = tdh_vp_flush(&to_tdx(vcpu)->vp);
+		if (unlikely(err && err != TDX_VCPU_NOT_ASSOCIATED)) {
+			/*
+			 * This function is called in IPI context. Do not use
+			 * printk to avoid console semaphore.
+			 * The caller prints out the error message, instead.
+			 */
+			if (err)
+				arg->err = err;
+		}
+	}
+
+	tdx_disassociate_vp(vcpu);
+}
+
+static void tdx_flush_vp_on_cpu(struct kvm_vcpu *vcpu)
+{
+	struct tdx_flush_vp_arg arg = {
+		.vcpu = vcpu,
+	};
+	int cpu = vcpu->cpu;
+
+	if (unlikely(cpu == -1))
+		return;
+
+	smp_call_function_single(cpu, tdx_flush_vp, &arg, 1);
+	if (KVM_BUG_ON(arg.err, vcpu->kvm))
+		pr_tdx_error(TDH_VP_FLUSH, arg.err);
+}
+
+void tdx_disable_virtualization_cpu(void)
+{
+	int cpu = raw_smp_processor_id();
+	struct list_head *tdvcpus = &per_cpu(associated_tdvcpus, cpu);
+	struct tdx_flush_vp_arg arg;
+	struct vcpu_tdx *tdx, *tmp;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	/* Safe variant needed as tdx_disassociate_vp() deletes the entry. */
+	list_for_each_entry_safe(tdx, tmp, tdvcpus, cpu_list) {
+		arg.vcpu = &tdx->vcpu;
+		tdx_flush_vp(&arg);
+	}
+	local_irq_restore(flags);
+}
+
 #define TDX_SEAMCALL_RETRIES 10000
 
 static void smp_func_do_phymem_cache_wb(void *unused)
@@ -281,22 +389,21 @@ void tdx_mmu_release_hkid(struct kvm *kvm)
 	bool packages_allocated, targets_allocated;
 	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
 	cpumask_var_t packages, targets;
-	u64 err;
+	struct kvm_vcpu *vcpu;
+	unsigned long j;
 	int i;
+	u64 err;
 
 	if (!is_hkid_assigned(kvm_tdx))
 		return;
 
-	/* KeyID has been allocated but guest is not yet configured */
-	if (!kvm_tdx->td.tdr_page) {
-		tdx_hkid_free(kvm_tdx);
-		return;
-	}
-
 	packages_allocated = zalloc_cpumask_var(&packages, GFP_KERNEL);
 	targets_allocated = zalloc_cpumask_var(&targets, GFP_KERNEL);
 	cpus_read_lock();
 
+	kvm_for_each_vcpu(j, vcpu, kvm)
+		tdx_flush_vp_on_cpu(vcpu);
+
 	/*
 	 * TDH.PHYMEM.CACHE.WB tries to acquire the TDX module global lock
 	 * and can fail with TDX_OPERAND_BUSY when it fails to get the lock.
@@ -310,6 +417,16 @@ void tdx_mmu_release_hkid(struct kvm *kvm)
 	 * After the above flushing vps, there should be no more vCPU
 	 * associations, as all vCPU fds have been released at this stage.
 	 */
+	err = tdh_mng_vpflushdone(&kvm_tdx->td);
+	if (err == TDX_FLUSHVP_NOT_DONE)
+		goto out;
+	if (KVM_BUG_ON(err, kvm)) {
+		pr_tdx_error(TDH_MNG_VPFLUSHDONE, err);
+		pr_err("tdh_mng_vpflushdone() failed. HKID %d is leaked.\n",
+		       kvm_tdx->hkid);
+		goto out;
+	}
+
 	for_each_online_cpu(i) {
 		if (packages_allocated &&
 		    cpumask_test_and_set_cpu(topology_physical_package_id(i),
@@ -335,6 +452,7 @@ void tdx_mmu_release_hkid(struct kvm *kvm)
 		tdx_hkid_free(kvm_tdx);
 	}
 
+out:
 	mutex_unlock(&tdx_lock);
 	cpus_read_unlock();
 	free_cpumask_var(targets);
@@ -488,6 +606,27 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
+void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
+{
+	struct vcpu_tdx *tdx = to_tdx(vcpu);
+
+	if (vcpu->cpu == cpu || !is_hkid_assigned(to_kvm_tdx(vcpu->kvm)))
+		return;
+
+	tdx_flush_vp_on_cpu(vcpu);
+
+	KVM_BUG_ON(cpu != raw_smp_processor_id(), vcpu->kvm);
+	local_irq_disable();
+	/*
+	 * Pairs with the smp_wmb() in tdx_disassociate_vp() to ensure
+	 * vcpu->cpu is read before tdx->cpu_list.
+	 */
+	smp_rmb();
+
+	list_add(&tdx->cpu_list, &per_cpu(associated_tdvcpus, cpu));
+	local_irq_enable();
+}
+
 void tdx_vcpu_free(struct kvm_vcpu *vcpu)
 {
 	struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
@@ -2044,7 +2183,11 @@ void tdx_cleanup(void)
 
 int __init tdx_bringup(void)
 {
-	int r;
+	int r, i;
+
+	/* tdx_disable_virtualization_cpu() uses associated_tdvcpus. */
+	for_each_possible_cpu(i)
+		INIT_LIST_HEAD(&per_cpu(associated_tdvcpus, i));
 
 	if (!enable_tdx)
 		return 0;

arch/x86/kvm/vmx/tdx.h

@@ -48,6 +48,8 @@ struct vcpu_tdx {
 
 	struct tdx_vp vp;
 
+	struct list_head cpu_list;
+
 	enum vcpu_tdx_state state;
 };
 

arch/x86/kvm/vmx/x86_ops.h

@@ -122,6 +122,7 @@ void vmx_cancel_hv_timer(struct kvm_vcpu *vcpu);
 void vmx_setup_mce(struct kvm_vcpu *vcpu);
 
 #ifdef CONFIG_KVM_INTEL_TDX
+void tdx_disable_virtualization_cpu(void);
 int tdx_vm_init(struct kvm *kvm);
 void tdx_mmu_release_hkid(struct kvm *kvm);
 void tdx_vm_destroy(struct kvm *kvm);
@@ -129,6 +130,7 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user *argp);
 
 int tdx_vcpu_create(struct kvm_vcpu *vcpu);
 void tdx_vcpu_free(struct kvm_vcpu *vcpu);
+void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
 
 int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp);
 
@@ -146,6 +148,7 @@ void tdx_flush_tlb_all(struct kvm_vcpu *vcpu);
 void tdx_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa, int root_level);
 int tdx_gmem_private_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn);
 #else
+static inline void tdx_disable_virtualization_cpu(void) {}
 static inline int tdx_vm_init(struct kvm *kvm) { return -EOPNOTSUPP; }
 static inline void tdx_mmu_release_hkid(struct kvm *kvm) {}
 static inline void tdx_vm_destroy(struct kvm *kvm) {}
@@ -153,6 +156,7 @@ static inline int tdx_vm_ioctl(struct kvm *kvm, void __user *argp) { return -EOP
 
 static inline int tdx_vcpu_create(struct kvm_vcpu *vcpu) { return -EOPNOTSUPP; }
 static inline void tdx_vcpu_free(struct kvm_vcpu *vcpu) {}
+static inline void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu) {}
 
 static inline int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp) { return -EOPNOTSUPP; }