xref: /linux/arch/x86/kvm/vmx/posted_intr.c

// SPDX-License-Identifier: GPL-2.0-only
#include <linux/kvm_host.h>

#include <asm/irq_remapping.h>
#include <asm/cpu.h>

#include "lapic.h"
#include "irq.h"
#include "posted_intr.h"
#include "trace.h"
#include "vmx.h"

/*
 * We maintain a per-CPU linked-list of vCPU, so in wakeup_handler() we
 * can find which vCPU should be waken up.
 */
static DEFINE_PER_CPU(struct list_head, blocked_vcpu_on_cpu);
static DEFINE_PER_CPU(spinlock_t, blocked_vcpu_on_cpu_lock);

static inline struct pi_desc *vcpu_to_pi_desc(struct kvm_vcpu *vcpu)
{
	return &(to_vmx(vcpu)->pi_desc);
}

void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
{
	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
	struct pi_desc old, new;
	unsigned int dest;

	/*
	 * In case of hot-plug or hot-unplug, we may have to undo
	 * vmx_vcpu_pi_put even if there is no assigned device.  And we
	 * always keep PI.NDST up to date for simplicity: it makes the
	 * code easier, and CPU migration is not a fast path.
	 */
	if (!pi_test_sn(pi_desc) && vcpu->cpu == cpu)
		return;

	/*
	 * If the 'nv' field is POSTED_INTR_WAKEUP_VECTOR, do not change
	 * PI.NDST: pi_post_block is the one expected to change PID.NDST and the
	 * wakeup handler expects the vCPU to be on the blocked_vcpu_list that
	 * matches PI.NDST. Otherwise, a vcpu may not be able to be woken up
	 * correctly.
	 */
	if (pi_desc->nv == POSTED_INTR_WAKEUP_VECTOR || vcpu->cpu == cpu) {
		pi_clear_sn(pi_desc);
		goto after_clear_sn;
	}

	/* The full case.  */
	do {
		old.control = new.control = pi_desc->control;

		dest = cpu_physical_id(cpu);

		if (x2apic_mode)
			new.ndst = dest;
		else
			new.ndst = (dest << 8) & 0xFF00;

		new.sn = 0;
	} while (cmpxchg64(&pi_desc->control, old.control,
			   new.control) != old.control);

after_clear_sn:

	/*
	 * Clear SN before reading the bitmap.  The VT-d firmware
	 * writes the bitmap and reads SN atomically (5.2.3 in the
	 * spec), so it doesn't really have a memory barrier that
	 * pairs with this, but we cannot do that and we need one.
	 */
	smp_mb__after_atomic();

	if (!pi_is_pir_empty(pi_desc))
		pi_set_on(pi_desc);
}

static bool vmx_can_use_vtd_pi(struct kvm *kvm)
{
	return irqchip_in_kernel(kvm) && enable_apicv &&
		kvm_arch_has_assigned_device(kvm) &&
		irq_remapping_cap(IRQ_POSTING_CAP);
}

void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
{
	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);

	if (!vmx_can_use_vtd_pi(vcpu->kvm))
		return;

	/* Set SN when the vCPU is preempted */
	if (vcpu->preempted)
		pi_set_sn(pi_desc);
}

static void __pi_post_block(struct kvm_vcpu *vcpu)
{
	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
	struct pi_desc old, new;
	unsigned int dest;

	do {
		old.control = new.control = pi_desc->control;
		WARN(old.nv != POSTED_INTR_WAKEUP_VECTOR,
		     "Wakeup handler not enabled while the VCPU is blocked\n");

		dest = cpu_physical_id(vcpu->cpu);

		if (x2apic_mode)
			new.ndst = dest;
		else
			new.ndst = (dest << 8) & 0xFF00;

		/* set 'NV' to 'notification vector' */
		new.nv = POSTED_INTR_VECTOR;
	} while (cmpxchg64(&pi_desc->control, old.control,
			   new.control) != old.control);

	if (!WARN_ON_ONCE(vcpu->pre_pcpu == -1)) {
		spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
		list_del(&vcpu->blocked_vcpu_list);
		spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
		vcpu->pre_pcpu = -1;
	}
}

/*
 * This routine does the following things for vCPU which is going
 * to be blocked if VT-d PI is enabled.
 * - Store the vCPU to the wakeup list, so when interrupts happen
 *   we can find the right vCPU to wake up.
 * - Change the Posted-interrupt descriptor as below:
 *      'NDST' <-- vcpu->pre_pcpu
 *      'NV' <-- POSTED_INTR_WAKEUP_VECTOR
 * - If 'ON' is set during this process, which means at least one
 *   interrupt is posted for this vCPU, we cannot block it, in
 *   this case, return 1, otherwise, return 0.
 *
 */
int pi_pre_block(struct kvm_vcpu *vcpu)
{
	unsigned int dest;
	struct pi_desc old, new;
	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);

	if (!vmx_can_use_vtd_pi(vcpu->kvm))
		return 0;

	WARN_ON(irqs_disabled());
	local_irq_disable();
	if (!WARN_ON_ONCE(vcpu->pre_pcpu != -1)) {
		vcpu->pre_pcpu = vcpu->cpu;
		spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
		list_add_tail(&vcpu->blocked_vcpu_list,
			      &per_cpu(blocked_vcpu_on_cpu,
				       vcpu->pre_pcpu));
		spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
	}

	do {
		old.control = new.control = pi_desc->control;

		WARN((pi_desc->sn == 1),
		     "Warning: SN field of posted-interrupts "
		     "is set before blocking\n");

		/*
		 * Since vCPU can be preempted during this process,
		 * vcpu->cpu could be different with pre_pcpu, we
		 * need to set pre_pcpu as the destination of wakeup
		 * notification event, then we can find the right vCPU
		 * to wakeup in wakeup handler if interrupts happen
		 * when the vCPU is in blocked state.
		 */
		dest = cpu_physical_id(vcpu->pre_pcpu);

		if (x2apic_mode)
			new.ndst = dest;
		else
			new.ndst = (dest << 8) & 0xFF00;

		/* set 'NV' to 'wakeup vector' */
		new.nv = POSTED_INTR_WAKEUP_VECTOR;
	} while (cmpxchg64(&pi_desc->control, old.control,
			   new.control) != old.control);

	/* We should not block the vCPU if an interrupt is posted for it.  */
	if (pi_test_on(pi_desc) == 1)
		__pi_post_block(vcpu);

	local_irq_enable();
	return (vcpu->pre_pcpu == -1);
}

void pi_post_block(struct kvm_vcpu *vcpu)
{
	if (vcpu->pre_pcpu == -1)
		return;

	WARN_ON(irqs_disabled());
	local_irq_disable();
	__pi_post_block(vcpu);
	local_irq_enable();
}

/*
 * Handler for POSTED_INTERRUPT_WAKEUP_VECTOR.
 */
void pi_wakeup_handler(void)
{
	struct kvm_vcpu *vcpu;
	int cpu = smp_processor_id();

	spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, cpu));
	list_for_each_entry(vcpu, &per_cpu(blocked_vcpu_on_cpu, cpu),
			blocked_vcpu_list) {
		struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);

		if (pi_test_on(pi_desc) == 1)
			kvm_vcpu_kick(vcpu);
	}
	spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, cpu));
}

void __init pi_init_cpu(int cpu)
{
	INIT_LIST_HEAD(&per_cpu(blocked_vcpu_on_cpu, cpu));
	spin_lock_init(&per_cpu(blocked_vcpu_on_cpu_lock, cpu));
}

bool pi_has_pending_interrupt(struct kvm_vcpu *vcpu)
{
	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);

	return pi_test_on(pi_desc) ||
		(pi_test_sn(pi_desc) && !pi_is_pir_empty(pi_desc));
}


/*
 * Bail out of the block loop if the VM has an assigned
 * device, but the blocking vCPU didn't reconfigure the
 * PI.NV to the wakeup vector, i.e. the assigned device
 * came along after the initial check in pi_pre_block().
 */
void vmx_pi_start_assignment(struct kvm *kvm)
{
	if (!irq_remapping_cap(IRQ_POSTING_CAP))
		return;

	kvm_make_all_cpus_request(kvm, KVM_REQ_UNBLOCK);
}

/*
 * pi_update_irte - set IRTE for Posted-Interrupts
 *
 * @kvm: kvm
 * @host_irq: host irq of the interrupt
 * @guest_irq: gsi of the interrupt
 * @set: set or unset PI
 * returns 0 on success, < 0 on failure
 */
int pi_update_irte(struct kvm *kvm, unsigned int host_irq, uint32_t guest_irq,
		   bool set)
{
	struct kvm_kernel_irq_routing_entry *e;
	struct kvm_irq_routing_table *irq_rt;
	struct kvm_lapic_irq irq;
	struct kvm_vcpu *vcpu;
	struct vcpu_data vcpu_info;
	int idx, ret = 0;

	if (!vmx_can_use_vtd_pi(kvm))
		return 0;

	idx = srcu_read_lock(&kvm->irq_srcu);
	irq_rt = srcu_dereference(kvm->irq_routing, &kvm->irq_srcu);
	if (guest_irq >= irq_rt->nr_rt_entries ||
	    hlist_empty(&irq_rt->map[guest_irq])) {
		pr_warn_once("no route for guest_irq %u/%u (broken user space?)\n",
			     guest_irq, irq_rt->nr_rt_entries);
		goto out;
	}

	hlist_for_each_entry(e, &irq_rt->map[guest_irq], link) {
		if (e->type != KVM_IRQ_ROUTING_MSI)
			continue;
		/*
		 * VT-d PI cannot support posting multicast/broadcast
		 * interrupts to a vCPU, we still use interrupt remapping
		 * for these kind of interrupts.
		 *
		 * For lowest-priority interrupts, we only support
		 * those with single CPU as the destination, e.g. user
		 * configures the interrupts via /proc/irq or uses
		 * irqbalance to make the interrupts single-CPU.
		 *
		 * We will support full lowest-priority interrupt later.
		 *
		 * In addition, we can only inject generic interrupts using
		 * the PI mechanism, refuse to route others through it.
		 */

		kvm_set_msi_irq(kvm, e, &irq);
		if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu) ||
		    !kvm_irq_is_postable(&irq)) {
			/*
			 * Make sure the IRTE is in remapped mode if
			 * we don't handle it in posted mode.
			 */
			ret = irq_set_vcpu_affinity(host_irq, NULL);
			if (ret < 0) {
				printk(KERN_INFO
				   "failed to back to remapped mode, irq: %u\n",
				   host_irq);
				goto out;
			}

			continue;
		}

		vcpu_info.pi_desc_addr = __pa(&to_vmx(vcpu)->pi_desc);
		vcpu_info.vector = irq.vector;

		trace_kvm_pi_irte_update(host_irq, vcpu->vcpu_id, e->gsi,
				vcpu_info.vector, vcpu_info.pi_desc_addr, set);

		if (set)
			ret = irq_set_vcpu_affinity(host_irq, &vcpu_info);
		else
			ret = irq_set_vcpu_affinity(host_irq, NULL);

		if (ret < 0) {
			printk(KERN_INFO "%s: failed to update PI IRTE\n",
					__func__);
			goto out;
		}
	}

	ret = 0;
out:
	srcu_read_unlock(&kvm->irq_srcu, idx);
	return ret;
}