/*
 * Copyright (C) 2017 ARM Ltd.
 * Author: Marc Zyngier <marc.zyngier@arm.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/irqdomain.h>
#include <linux/kvm_host.h>
#include <linux/irqchip/arm-gic-v3.h>

#include "vgic.h"

/*
 * How KVM uses GICv4 (insert rude comments here):
 *
 * The vgic-v4 layer acts as a bridge between several entities:
 * - The GICv4 ITS representation offered by the ITS driver
 * - VFIO, which is in charge of the PCI endpoint
 * - The virtual ITS, which is the only thing the guest sees
 *
 * The configuration of VLPIs is triggered by a callback from VFIO,
 * instructing KVM that a PCI device has been configured to deliver
 * MSIs to a vITS.
 *
 * kvm_vgic_v4_set_forwarding() is thus called with the routing entry,
 * and this is used to find the corresponding vITS data structures
 * (ITS instance, device, event and irq) using a process that is
 * extremely similar to the injection of an MSI.
 *
 * At this stage, we can link the guest's view of an LPI (uniquely
 * identified by the routing entry) and the host irq, using the GICv4
 * driver mapping operation. Should the mapping succeed, we've then
 * successfully upgraded the guest's LPI to a VLPI. We can then start
 * with updating GICv4's view of the property table and generating an
 * INValidation in order to kickstart the delivery of this VLPI to the
 * guest directly, without software intervention. Well, almost.
 *
 * When the PCI endpoint is deconfigured, this operation is reversed
 * with VFIO calling kvm_vgic_v4_unset_forwarding().
 *
 * Once the VLPI has been mapped, it needs to follow any change the
 * guest performs on its LPI through the vITS. For that, a number of
 * command handlers have hooks to communicate these changes to the HW:
 * - Any invalidation triggers a call to its_prop_update_vlpi()
 * - The INT command results in a irq_set_irqchip_state(), which
 *   generates an INT on the corresponding VLPI.
 * - The CLEAR command results in a irq_set_irqchip_state(), which
 *   generates an CLEAR on the corresponding VLPI.
 * - DISCARD translates into an unmap, similar to a call to
 *   kvm_vgic_v4_unset_forwarding().
 * - MOVI is translated by an update of the existing mapping, changing
 *   the target vcpu, resulting in a VMOVI being generated.
 * - MOVALL is translated by a string of mapping updates (similar to
 *   the handling of MOVI). MOVALL is horrible.
 *
 * Note that a DISCARD/MAPTI sequence emitted from the guest without
 * reprogramming the PCI endpoint after MAPTI does not result in a
 * VLPI being mapped, as there is no callback from VFIO (the guest
 * will get the interrupt via the normal SW injection). Fixing this is
 * not trivial, and requires some horrible messing with the VFIO
 * internals. Not fun. Don't do that.
 *
 * Then there is the scheduling. Each time a vcpu is about to run on a
 * physical CPU, KVM must tell the corresponding redistributor about
 * it. And if we've migrated our vcpu from one CPU to another, we must
 * tell the ITS (so that the messages reach the right redistributor).
 * This is done in two steps: first issue a irq_set_affinity() on the
 * irq corresponding to the vcpu, then call its_schedule_vpe(). You
 * must be in a non-preemptible context. On exit, another call to
 * its_schedule_vpe() tells the redistributor that we're done with the
 * vcpu.
 *
 * Finally, the doorbell handling: Each vcpu is allocated an interrupt
 * which will fire each time a VLPI is made pending whilst the vcpu is
 * not running. Each time the vcpu gets blocked, the doorbell
 * interrupt gets enabled. When the vcpu is unblocked (for whatever
 * reason), the doorbell interrupt is disabled.
 */

#define DB_IRQ_FLAGS    (IRQ_NOAUTOEN | IRQ_DISABLE_UNLAZY | IRQ_NO_BALANCING)

static irqreturn_t vgic_v4_doorbell_handler(int irq, void *info)
{
        struct kvm_vcpu *vcpu = info;

        vcpu->arch.vgic_cpu.vgic_v3.its_vpe.pending_last = true;
        kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);
        kvm_vcpu_kick(vcpu);

        return IRQ_HANDLED;
}

/**
 * vgic_v4_init - Initialize the GICv4 data structures
 * @kvm:        Pointer to the VM being initialized
 *
 * We may be called each time a vITS is created, or when the
 * vgic is initialized. This relies on kvm->lock to be
 * held. In both cases, the number of vcpus should now be
 * fixed.
 */
int vgic_v4_init(struct kvm *kvm)
{
        struct vgic_dist *dist = &kvm->arch.vgic;
        struct kvm_vcpu *vcpu;
        int i, nr_vcpus, ret;

        if (!kvm_vgic_global_state.has_gicv4)
                return 0; /* Nothing to see here... move along. */

        if (dist->its_vm.vpes)
                return 0;

        nr_vcpus = atomic_read(&kvm->online_vcpus);

        dist->its_vm.vpes = kzalloc(sizeof(*dist->its_vm.vpes) * nr_vcpus,
                                    GFP_KERNEL);
        if (!dist->its_vm.vpes)
                return -ENOMEM;

        dist->its_vm.nr_vpes = nr_vcpus;

        kvm_for_each_vcpu(i, vcpu, kvm)
                dist->its_vm.vpes[i] = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;

        ret = its_alloc_vcpu_irqs(&dist->its_vm);
        if (ret < 0) {
                kvm_err("VPE IRQ allocation failure\n");
                kfree(dist->its_vm.vpes);
                dist->its_vm.nr_vpes = 0;
                dist->its_vm.vpes = NULL;
                return ret;
        }

        kvm_for_each_vcpu(i, vcpu, kvm) {
                int irq = dist->its_vm.vpes[i]->irq;

                /*
                 * Don't automatically enable the doorbell, as we're
                 * flipping it back and forth when the vcpu gets
                 * blocked. Also disable the lazy disabling, as the
                 * doorbell could kick us out of the guest too
                 * early...
                 */
                irq_set_status_flags(irq, DB_IRQ_FLAGS);
                ret = request_irq(irq, vgic_v4_doorbell_handler,
                                  0, "vcpu", vcpu);
                if (ret) {
                        kvm_err("failed to allocate vcpu IRQ%d\n", irq);
                        /*
                         * Trick: adjust the number of vpes so we know
                         * how many to nuke on teardown...
                         */
                        dist->its_vm.nr_vpes = i;
                        break;
                }
        }

        if (ret)
                vgic_v4_teardown(kvm);

        return ret;
}

/**
 * vgic_v4_teardown - Free the GICv4 data structures
 * @kvm:        Pointer to the VM being destroyed
 *
 * Relies on kvm->lock to be held.
 */
void vgic_v4_teardown(struct kvm *kvm)
{
        struct its_vm *its_vm = &kvm->arch.vgic.its_vm;
        int i;

        if (!its_vm->vpes)
                return;

        for (i = 0; i < its_vm->nr_vpes; i++) {
                struct kvm_vcpu *vcpu = kvm_get_vcpu(kvm, i);
                int irq = its_vm->vpes[i]->irq;

                irq_clear_status_flags(irq, DB_IRQ_FLAGS);
                free_irq(irq, vcpu);
        }

        its_free_vcpu_irqs(its_vm);
        kfree(its_vm->vpes);
        its_vm->nr_vpes = 0;
        its_vm->vpes = NULL;
}

int vgic_v4_sync_hwstate(struct kvm_vcpu *vcpu)
{
        if (!vgic_supports_direct_msis(vcpu->kvm))
                return 0;

        return its_schedule_vpe(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe, false);
}

int vgic_v4_flush_hwstate(struct kvm_vcpu *vcpu)
{
        int irq = vcpu->arch.vgic_cpu.vgic_v3.its_vpe.irq;
        int err;

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

        /*
         * Before making the VPE resident, make sure the redistributor
         * corresponding to our current CPU expects us here. See the
         * doc in drivers/irqchip/irq-gic-v4.c to understand how this
         * turns into a VMOVP command at the ITS level.
         */
        err = irq_set_affinity(irq, cpumask_of(smp_processor_id()));
        if (err)
                return err;

        err = its_schedule_vpe(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe, true);
        if (err)
                return err;

        /*
         * Now that the VPE is resident, let's get rid of a potential
         * doorbell interrupt that would still be pending.
         */
        err = irq_set_irqchip_state(irq, IRQCHIP_STATE_PENDING, false);

        return err;
}

static struct vgic_its *vgic_get_its(struct kvm *kvm,
                                     struct kvm_kernel_irq_routing_entry *irq_entry)
{
        struct kvm_msi msi  = (struct kvm_msi) {
                .address_lo     = irq_entry->msi.address_lo,
                .address_hi     = irq_entry->msi.address_hi,
                .data           = irq_entry->msi.data,
                .flags          = irq_entry->msi.flags,
                .devid          = irq_entry->msi.devid,
        };

        return vgic_msi_to_its(kvm, &msi);
}

int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq,
                               struct kvm_kernel_irq_routing_entry *irq_entry)
{
        struct vgic_its *its;
        struct vgic_irq *irq;
        struct its_vlpi_map map;
        int ret;

        if (!vgic_supports_direct_msis(kvm))
                return 0;

        /*
         * Get the ITS, and escape early on error (not a valid
         * doorbell for any of our vITSs).
         */
        its = vgic_get_its(kvm, irq_entry);
        if (IS_ERR(its))
                return 0;

        mutex_lock(&its->its_lock);

        /* Perform then actual DevID/EventID -> LPI translation. */
        ret = vgic_its_resolve_lpi(kvm, its, irq_entry->msi.devid,
                                   irq_entry->msi.data, &irq);
        if (ret)
                goto out;

        /*
         * Emit the mapping request. If it fails, the ITS probably
         * isn't v4 compatible, so let's silently bail out. Holding
         * the ITS lock should ensure that nothing can modify the
         * target vcpu.
         */
        map = (struct its_vlpi_map) {
                .vm             = &kvm->arch.vgic.its_vm,
                .vpe            = &irq->target_vcpu->arch.vgic_cpu.vgic_v3.its_vpe,
                .vintid         = irq->intid,
                .properties     = ((irq->priority & 0xfc) |
                                   (irq->enabled ? LPI_PROP_ENABLED : 0) |
                                   LPI_PROP_GROUP1),
                .db_enabled     = true,
        };

        ret = its_map_vlpi(virq, &map);
        if (ret)
                goto out;

        irq->hw         = true;
        irq->host_irq   = virq;

out:
        mutex_unlock(&its->its_lock);
        return ret;
}

int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int virq,
                                 struct kvm_kernel_irq_routing_entry *irq_entry)
{
        struct vgic_its *its;
        struct vgic_irq *irq;
        int ret;

        if (!vgic_supports_direct_msis(kvm))
                return 0;

        /*
         * Get the ITS, and escape early on error (not a valid
         * doorbell for any of our vITSs).
         */
        its = vgic_get_its(kvm, irq_entry);
        if (IS_ERR(its))
                return 0;

        mutex_lock(&its->its_lock);

        ret = vgic_its_resolve_lpi(kvm, its, irq_entry->msi.devid,
                                   irq_entry->msi.data, &irq);
        if (ret)
                goto out;

        WARN_ON(!(irq->hw && irq->host_irq == virq));
        if (irq->hw) {
                irq->hw = false;
                ret = its_unmap_vlpi(virq);
        }

out:
        mutex_unlock(&its->its_lock);
        return ret;
}

void kvm_vgic_v4_enable_doorbell(struct kvm_vcpu *vcpu)
{
        if (vgic_supports_direct_msis(vcpu->kvm)) {
                int irq = vcpu->arch.vgic_cpu.vgic_v3.its_vpe.irq;
                if (irq)
                        enable_irq(irq);
        }
}

void kvm_vgic_v4_disable_doorbell(struct kvm_vcpu *vcpu)
{
        if (vgic_supports_direct_msis(vcpu->kvm)) {
                int irq = vcpu->arch.vgic_cpu.vgic_v3.its_vpe.irq;
                if (irq)
                        disable_irq(irq);
        }
}