posted_intr.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  3
  4#include <linux/kvm_host.h>
  5#include <linux/kvm_irqfd.h>
  6
  7#include <asm/irq_remapping.h>
  8#include <asm/cpu.h>
  9
 10#include "lapic.h"
 11#include "irq.h"
 12#include "posted_intr.h"
 13#include "trace.h"
 14#include "vmx.h"
 15#include "tdx.h"
 16
 17/*
 18 * Maintain a per-CPU list of vCPUs that need to be awakened by wakeup_handler()
 19 * when a WAKEUP_VECTOR interrupted is posted.  vCPUs are added to the list when
 20 * the vCPU is scheduled out and is blocking (e.g. in HLT) with IRQs enabled.
 21 * The vCPUs posted interrupt descriptor is updated at the same time to set its
 22 * notification vector to WAKEUP_VECTOR, so that posted interrupt from devices
 23 * wake the target vCPUs.  vCPUs are removed from the list and the notification
 24 * vector is reset when the vCPU is scheduled in.
 25 */
 26static DEFINE_PER_CPU(struct list_head, wakeup_vcpus_on_cpu);
 27/*
 28 * Protect the per-CPU list with a per-CPU spinlock to handle task migration.
 29 * When a blocking vCPU is awakened _and_ migrated to a different pCPU, the
 30 * ->sched_in() path will need to take the vCPU off the list of the _previous_
 31 * CPU.  IRQs must be disabled when taking this lock, otherwise deadlock will
 32 * occur if a wakeup IRQ arrives and attempts to acquire the lock.
 33 */
 34static DEFINE_PER_CPU(raw_spinlock_t, wakeup_vcpus_on_cpu_lock);
 35
 36#define PI_LOCK_SCHED_OUT SINGLE_DEPTH_NESTING
 37
 38static struct pi_desc *vcpu_to_pi_desc(struct kvm_vcpu *vcpu)
 39{
 40	return &(to_vt(vcpu)->pi_desc);
 41}
 42
 43static int pi_try_set_control(struct pi_desc *pi_desc, u64 *pold, u64 new)
 44{
 45	/*
 46	 * PID.ON can be set at any time by a different vCPU or by hardware,
 47	 * e.g. a device.  PID.control must be written atomically, and the
 48	 * update must be retried with a fresh snapshot an ON change causes
 49	 * the cmpxchg to fail.
 50	 */
 51	if (!try_cmpxchg64(&pi_desc->control, pold, new))
 52		return -EBUSY;
 53
 54	return 0;
 55}
 56
 57void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
 58{
 59	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
 60	struct vcpu_vt *vt = to_vt(vcpu);
 61	struct pi_desc old, new;
 62	unsigned long flags;
 63	unsigned int dest;
 64
 65	/*
 66	 * To simplify hot-plug and dynamic toggling of APICv, keep PI.NDST and
 67	 * PI.SN up-to-date even if there is no assigned device or if APICv is
 68	 * deactivated due to a dynamic inhibit bit, e.g. for Hyper-V's SyncIC.
 69	 */
 70	if (!enable_apicv || !lapic_in_kernel(vcpu))
 71		return;
 72
 73	/*
 74	 * If the vCPU wasn't on the wakeup list and wasn't migrated, then the
 75	 * full update can be skipped as neither the vector nor the destination
 76	 * needs to be changed.  Clear SN even if there is no assigned device,
 77	 * again for simplicity.
 78	 */
 79	if (pi_desc->nv != POSTED_INTR_WAKEUP_VECTOR && vcpu->cpu == cpu) {
 80		if (pi_test_and_clear_sn(pi_desc))
 81			goto after_clear_sn;
 82		return;
 83	}
 84
 85	local_irq_save(flags);
 86
 87	/*
 88	 * If the vCPU was waiting for wakeup, remove the vCPU from the wakeup
 89	 * list of the _previous_ pCPU, which will not be the same as the
 90	 * current pCPU if the task was migrated.
 91	 */
 92	if (pi_desc->nv == POSTED_INTR_WAKEUP_VECTOR) {
 93		raw_spinlock_t *spinlock = &per_cpu(wakeup_vcpus_on_cpu_lock, vcpu->cpu);
 94
 95		/*
 96		 * In addition to taking the wakeup lock for the regular/IRQ
 97		 * context, tell lockdep it is being taken for the "sched out"
 98		 * context as well.  vCPU loads happens in task context, and
 99		 * this is taking the lock of the *previous* CPU, i.e. can race
100		 * with both the scheduler and the wakeup handler.
101		 */
102		raw_spin_lock(spinlock);
103		spin_acquire(&spinlock->dep_map, PI_LOCK_SCHED_OUT, 0, _RET_IP_);
104		list_del(&vt->pi_wakeup_list);
105		spin_release(&spinlock->dep_map, _RET_IP_);
106		raw_spin_unlock(spinlock);
107	}
108
109	dest = cpu_physical_id(cpu);
110	if (!x2apic_mode)
111		dest = (dest << 8) & 0xFF00;
112
113	old.control = READ_ONCE(pi_desc->control);
114	do {
115		new.control = old.control;
116
117		/*
118		 * Clear SN (as above) and refresh the destination APIC ID to
119		 * handle task migration (@cpu != vcpu->cpu).
120		 */
121		new.ndst = dest;
122		__pi_clear_sn(&new);
123
124		/*
125		 * Restore the notification vector; in the blocking case, the
126		 * descriptor was modified on "put" to use the wakeup vector.
127		 */
128		new.nv = POSTED_INTR_VECTOR;
129	} while (pi_try_set_control(pi_desc, &old.control, new.control));
130
131	local_irq_restore(flags);
132
133after_clear_sn:
134
135	/*
136	 * Clear SN before reading the bitmap.  The VT-d firmware
137	 * writes the bitmap and reads SN atomically (5.2.3 in the
138	 * spec), so it doesn't really have a memory barrier that
139	 * pairs with this, but we cannot do that and we need one.
140	 */
141	smp_mb__after_atomic();
142
143	if (!pi_is_pir_empty(pi_desc))
144		pi_set_on(pi_desc);
145}
146
147static bool vmx_can_use_vtd_pi(struct kvm *kvm)
148{
149	/*
150	 * Note, reading the number of possible bypass IRQs can race with a
151	 * bypass IRQ being attached to the VM.  vmx_pi_start_bypass() ensures
152	 * blockng vCPUs will see an elevated count or get KVM_REQ_UNBLOCK.
153	 */
154	return irqchip_in_kernel(kvm) && kvm_arch_has_irq_bypass() &&
155	       READ_ONCE(kvm->arch.nr_possible_bypass_irqs);
156}
157
158/*
159 * Put the vCPU on this pCPU's list of vCPUs that needs to be awakened and set
160 * WAKEUP as the notification vector in the PI descriptor.
161 */
162static void pi_enable_wakeup_handler(struct kvm_vcpu *vcpu)
163{
164	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
165	struct vcpu_vt *vt = to_vt(vcpu);
166	struct pi_desc old, new;
167
168	lockdep_assert_irqs_disabled();
169
170	/*
171	 * Acquire the wakeup lock using the "sched out" context to workaround
172	 * a lockdep false positive.  When this is called, schedule() holds
173	 * various per-CPU scheduler locks.  When the wakeup handler runs, it
174	 * holds this CPU's wakeup lock while calling try_to_wake_up(), which
175	 * can eventually take the aforementioned scheduler locks, which causes
176	 * lockdep to assume there is deadlock.
177	 *
178	 * Deadlock can't actually occur because IRQs are disabled for the
179	 * entirety of the sched_out critical section, i.e. the wakeup handler
180	 * can't run while the scheduler locks are held.
181	 */
182	raw_spin_lock_nested(&per_cpu(wakeup_vcpus_on_cpu_lock, vcpu->cpu),
183			     PI_LOCK_SCHED_OUT);
184	list_add_tail(&vt->pi_wakeup_list,
185		      &per_cpu(wakeup_vcpus_on_cpu, vcpu->cpu));
186	raw_spin_unlock(&per_cpu(wakeup_vcpus_on_cpu_lock, vcpu->cpu));
187
188	WARN(pi_test_sn(pi_desc), "PI descriptor SN field set before blocking");
189
190	old.control = READ_ONCE(pi_desc->control);
191	do {
192		/* set 'NV' to 'wakeup vector' */
193		new.control = old.control;
194		new.nv = POSTED_INTR_WAKEUP_VECTOR;
195	} while (pi_try_set_control(pi_desc, &old.control, new.control));
196
197	/*
198	 * Send a wakeup IPI to this CPU if an interrupt may have been posted
199	 * before the notification vector was updated, in which case the IRQ
200	 * will arrive on the non-wakeup vector.  An IPI is needed as calling
201	 * try_to_wake_up() from ->sched_out() isn't allowed (IRQs are not
202	 * enabled until it is safe to call try_to_wake_up() on the task being
203	 * scheduled out).
204	 */
205	if (pi_test_on(&new))
206		__apic_send_IPI_self(POSTED_INTR_WAKEUP_VECTOR);
207}
208
209static bool vmx_needs_pi_wakeup(struct kvm_vcpu *vcpu)
210{
211	/*
212	 * The default posted interrupt vector does nothing when
213	 * invoked outside guest mode.   Return whether a blocked vCPU
214	 * can be the target of posted interrupts, as is the case when
215	 * using either IPI virtualization or VT-d PI, so that the
216	 * notification vector is switched to the one that calls
217	 * back to the pi_wakeup_handler() function.
218	 */
219	return (vmx_can_use_ipiv(vcpu) && !is_td_vcpu(vcpu)) ||
220		vmx_can_use_vtd_pi(vcpu->kvm);
221}
222
223void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
224{
225	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
226
227	if (!vmx_needs_pi_wakeup(vcpu))
228		return;
229
230	/*
231	 * If the vCPU is blocking with IRQs enabled and ISN'T being preempted,
232	 * enable the wakeup handler so that notification IRQ wakes the vCPU as
233	 * expected.  There is no need to enable the wakeup handler if the vCPU
234	 * is preempted between setting its wait state and manually scheduling
235	 * out, as the task is still runnable, i.e. doesn't need a wake event
236	 * from KVM to be scheduled in.
237	 *
238	 * If the wakeup handler isn't being enabled, Suppress Notifications as
239	 * the cost of propagating PIR.IRR to PID.ON is negligible compared to
240	 * the cost of a spurious IRQ, and vCPU put/load is a slow path.
241	 */
242	if (!vcpu->preempted && kvm_vcpu_is_blocking(vcpu) &&
243	    ((is_td_vcpu(vcpu) && tdx_interrupt_allowed(vcpu)) ||
244	     (!is_td_vcpu(vcpu) && !vmx_interrupt_blocked(vcpu))))
245		pi_enable_wakeup_handler(vcpu);
246	else
247		pi_set_sn(pi_desc);
248}
249
250/*
251 * Handler for POSTED_INTERRUPT_WAKEUP_VECTOR.
252 */
253void pi_wakeup_handler(void)
254{
255	int cpu = smp_processor_id();
256	struct list_head *wakeup_list = &per_cpu(wakeup_vcpus_on_cpu, cpu);
257	raw_spinlock_t *spinlock = &per_cpu(wakeup_vcpus_on_cpu_lock, cpu);
258	struct vcpu_vt *vt;
259
260	raw_spin_lock(spinlock);
261	list_for_each_entry(vt, wakeup_list, pi_wakeup_list) {
262
263		if (pi_test_on(&vt->pi_desc))
264			kvm_vcpu_wake_up(vt_to_vcpu(vt));
265	}
266	raw_spin_unlock(spinlock);
267}
268
269void __init pi_init_cpu(int cpu)
270{
271	INIT_LIST_HEAD(&per_cpu(wakeup_vcpus_on_cpu, cpu));
272	raw_spin_lock_init(&per_cpu(wakeup_vcpus_on_cpu_lock, cpu));
273}
274
275void pi_apicv_pre_state_restore(struct kvm_vcpu *vcpu)
276{
277	struct pi_desc *pi = vcpu_to_pi_desc(vcpu);
278
279	pi_clear_on(pi);
280	memset(pi->pir, 0, sizeof(pi->pir));
281}
282
283bool pi_has_pending_interrupt(struct kvm_vcpu *vcpu)
284{
285	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
286
287	return pi_test_on(pi_desc) ||
288		(pi_test_sn(pi_desc) && !pi_is_pir_empty(pi_desc));
289}
290
291
292/*
293 * Kick all vCPUs when the first possible bypass IRQ is attached to a VM, as
294 * blocking vCPUs may scheduled out without reconfiguring PID.NV to the wakeup
295 * vector, i.e. if the bypass IRQ came along after vmx_vcpu_pi_put().
296 */
297void vmx_pi_start_bypass(struct kvm *kvm)
298{
299	if (WARN_ON_ONCE(!vmx_can_use_vtd_pi(kvm)))
300		return;
301
302	kvm_make_all_cpus_request(kvm, KVM_REQ_UNBLOCK);
303}
304
305int vmx_pi_update_irte(struct kvm_kernel_irqfd *irqfd, struct kvm *kvm,
306		       unsigned int host_irq, uint32_t guest_irq,
307		       struct kvm_vcpu *vcpu, u32 vector)
308{
309	if (vcpu) {
310		struct intel_iommu_pi_data pi_data = {
311			.pi_desc_addr = __pa(vcpu_to_pi_desc(vcpu)),
312			.vector = vector,
313		};
314
315		return irq_set_vcpu_affinity(host_irq, &pi_data);
316	} else {
317		return irq_set_vcpu_affinity(host_irq, NULL);
318	}
319}