torvalds/linux

// SPDX-License-Identifier: GPL-2.0
/*
 * KVM coalesced MMIO
 *
 * Copyright (c) 2008 Bull S.A.S.
 * Copyright 2009 Red Hat, Inc. and/or its affiliates.
 *
 *  Author: Laurent Vivier <Laurent.Vivier@bull.net>
 *
 */

#include <kvm/iodev.h>

#include <linux/kvm_host.h>
#include <linux/slab.h>
#include <linux/kvm.h>

#include "coalesced_mmio.h"

static inline struct kvm_coalesced_mmio_dev *to_mmio(struct kvm_io_device *dev)
{
    return container_of(dev, struct kvm_coalesced_mmio_dev, dev);
}

static int coalesced_mmio_in_range(struct kvm_coalesced_mmio_dev *dev,
                   gpa_t addr, int len)
{
    /* is it in a batchable area ?
     * (addr,len) is fully included in
     * (zone->addr, zone->size)
     */
    if (len < 0)
        return 0;
    if (addr + len < addr)
        return 0;
    if (addr < dev->zone.addr)
        return 0;
    if (addr + len > dev->zone.addr + dev->zone.size)
        return 0;
    return 1;
}

static int coalesced_mmio_has_room(struct kvm_coalesced_mmio_dev *dev, u32 last)
{
    struct kvm_coalesced_mmio_ring *ring;
    unsigned avail;

    /* Are we able to batch it ? */

    /* last is the first free entry
     * check if we don't meet the first used entry
     * there is always one unused entry in the buffer
     */
    ring = dev->kvm->coalesced_mmio_ring;
    avail = (ring->first - last - 1) % KVM_COALESCED_MMIO_MAX;
    if (avail == 0) {
        /* full */
        return 0;
    }

    return 1;
}

static int coalesced_mmio_write(struct kvm_vcpu *vcpu,
                struct kvm_io_device *this, gpa_t addr,
                int len, const void *val)
{
    struct kvm_coalesced_mmio_dev *dev = to_mmio(this);
    struct kvm_coalesced_mmio_ring *ring = dev->kvm->coalesced_mmio_ring;
    __u32 insert;

    if (!coalesced_mmio_in_range(dev, addr, len))
        return -EOPNOTSUPP;

    spin_lock(&dev->kvm->ring_lock);

    insert = READ_ONCE(ring->last);
    if (!coalesced_mmio_has_room(dev, insert) ||
        insert >= KVM_COALESCED_MMIO_MAX) {
        spin_unlock(&dev->kvm->ring_lock);
        return -EOPNOTSUPP;
    }

    /* copy data in first free entry of the ring */

    ring->coalesced_mmio[insert].phys_addr = addr;
    ring->coalesced_mmio[insert].len = len;
    memcpy(ring->coalesced_mmio[insert].data, val, len);
    ring->coalesced_mmio[insert].pio = dev->zone.pio;
    smp_wmb();
    ring->last = (insert + 1) % KVM_COALESCED_MMIO_MAX;
    spin_unlock(&dev->kvm->ring_lock);
    return 0;
}

static void coalesced_mmio_destructor(struct kvm_io_device *this)
{
    struct kvm_coalesced_mmio_dev *dev = to_mmio(this);

    list_del(&dev->list);

    kfree(dev);
}

static const struct kvm_io_device_ops coalesced_mmio_ops = {
    .write      = coalesced_mmio_write,
    .destructor = coalesced_mmio_destructor,
};

int kvm_coalesced_mmio_init(struct kvm *kvm)
{
    struct page *page;

    page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
    if (!page)
        return -ENOMEM;

    kvm->coalesced_mmio_ring = page_address(page);

    /*
     * We're using this spinlock to sync access to the coalesced ring.
     * The list doesn't need its own lock since device registration and
     * unregistration should only happen when kvm->slots_lock is held.
     */
    spin_lock_init(&kvm->ring_lock);
    INIT_LIST_HEAD(&kvm->coalesced_zones);

    return 0;
}

void kvm_coalesced_mmio_free(struct kvm *kvm)
{
    if (kvm->coalesced_mmio_ring)
        free_page((unsigned long)kvm->coalesced_mmio_ring);
}

int kvm_vm_ioctl_register_coalesced_mmio(struct kvm *kvm,
                     struct kvm_coalesced_mmio_zone *zone)
{
    int ret;
    struct kvm_coalesced_mmio_dev *dev;

    if (zone->pio != 1 && zone->pio != 0)
        return -EINVAL;

    dev = kzalloc(sizeof(struct kvm_coalesced_mmio_dev),
              GFP_KERNEL_ACCOUNT);
    if (!dev)
        return -ENOMEM;

    kvm_iodevice_init(&dev->dev, &coalesced_mmio_ops);
    dev->kvm = kvm;
    dev->zone = *zone;

    mutex_lock(&kvm->slots_lock);
    ret = kvm_io_bus_register_dev(kvm,
                zone->pio ? KVM_PIO_BUS : KVM_MMIO_BUS,
                zone->addr, zone->size, &dev->dev);
    if (ret < 0)
        goto out_free_dev;
    list_add_tail(&dev->list, &kvm->coalesced_zones);
    mutex_unlock(&kvm->slots_lock);

    return 0;

out_free_dev:
    mutex_unlock(&kvm->slots_lock);
    kfree(dev);

    return ret;
}

int kvm_vm_ioctl_unregister_coalesced_mmio(struct kvm *kvm,
                       struct kvm_coalesced_mmio_zone *zone)
{
    struct kvm_coalesced_mmio_dev *dev, *tmp;
    int r;

    if (zone->pio != 1 && zone->pio != 0)
        return -EINVAL;

    mutex_lock(&kvm->slots_lock);

    list_for_each_entry_safe(dev, tmp, &kvm->coalesced_zones, list) {
        if (zone->pio == dev->zone.pio &&
            coalesced_mmio_in_range(dev, zone->addr, zone->size)) {
            r = kvm_io_bus_unregister_dev(kvm,
                zone->pio ? KVM_PIO_BUS : KVM_MMIO_BUS, &dev->dev);
            /*
             * On failure, unregister destroys all devices on the
             * bus, including the target device. There's no need
             * to restart the walk as there aren't any zones left.
             */
            if (r)
                break;
        }
    }

    mutex_unlock(&kvm->slots_lock);

    /*
     * Ignore the result of kvm_io_bus_unregister_dev(), from userspace's
     * perspective, the coalesced MMIO is most definitely unregistered.
     */
    return 0;
}